MDPI - Publisher of Open Access Journals

Open AccessArticle Transmission Power and Antenna Allocation for Energy-Efficient RF Energy Harvesting Networks with Massive MIMO

by Yu Min Hwang, Ji Ho Park, Yoan Shin, Jin Young Kim and Dong In Kim

Energies 2017, 10(6), 802; doi:10.3390/en10060802

Received: 22 February 2017 / Revised: 1 June 2017 / Accepted: 9 June 2017 / Published: 13 June 2017

Viewed by 425 | PDF Full-text (2576 KB) | HTML Full-text | XML Full-text

Abstract

The optimum transmission strategy for maximizing energy efficiency (EE) of a multi-user massive multiple-input multiple-output (MIMO) system in radio frequency energy harvesting networks is investigated. We focus on dynamic time-switching (TS) antennas, to avoid the practical problems of power-splitting antennas, such as complex

[...] Read more.

The optimum transmission strategy for maximizing energy efficiency (EE) of a multi-user massive multiple-input multiple-output (MIMO) system in radio frequency energy harvesting networks is investigated. We focus on dynamic time-switching (TS) antennas, to avoid the practical problems of power-splitting antennas, such as complex architectures, power loss and signal distortion when splitting the power of the received signal into power for information decoding (ID) and energy harvesting (EH). However, since a single TS antenna cannot serve ID and EH simultaneously, the MIMO system is considered in this paper. We thus formulate an EE optimization problem and propose an iterative algorithm as a tractable solution, including an antenna selection strategy to optimally switch each TS antenna between ID mode and EH mode using nonlinear fractional programming and the Lagrange dual method. Further, the problem is solved under practical constraints of maximum transmission power and outage probabilities for a minimum amount of harvested power and rate capacity for each user. Simulation results show that the proposed algorithm is more energy-efficient than that of baseline schemes, and demonstrates the trade-off between the required amount of harvested power and energy efficiency. Full article

(This article belongs to the Section Electrical Power and Energy System)

► Figures

Figure 1

Open AccessArticle In-Flight Calibration of GF-1/WFV Visible Channels Using Rayleigh Scattering

by Xingfeng Chen, Jin Xing, Li Liu, Zhengqiang Li, Xiaodong Mei, Qiaoyan Fu, Yisong Xie, Bangyu Ge, Kaitao Li and Hua Xu

Remote Sens. 2017, 9(6), 513; doi:10.3390/rs9060513

Received: 8 January 2017 / Revised: 11 May 2017 / Accepted: 19 May 2017 / Published: 23 May 2017

Viewed by 441 | PDF Full-text (3642 KB) | HTML Full-text | XML Full-text

Abstract

China is planning to launch more and more optical remote-sensing satellites with high spatial resolution and multistep gains. Field calibration, the current operational method of satellite in-flight radiometric calibration, still does not have enough capacity to meet these demands. Gaofen-1 (GF-1), as the

[...] Read more.

China is planning to launch more and more optical remote-sensing satellites with high spatial resolution and multistep gains. Field calibration, the current operational method of satellite in-flight radiometric calibration, still does not have enough capacity to meet these demands. Gaofen-1 (GF-1), as the first satellite of the Chinese High-resolution Earth Observation System, has been specially arranged to obtain 22 images over clean ocean areas using the Wide Field Viewing camera. Following this, Rayleigh scattering calibration was carried out for the visible channels with these images after the appropriate data processing steps. To guarantee a high calibration precision, uncertainty was analyzed in advance taking into account ozone, aerosol optical depth (AOD), seawater salinity, chlorophyll concentration, wind speed and solar zenith angle. AOD and wind speed were found to be the biggest error sources, which were also closely coupled to the solar zenith angle. Therefore, the best sample data for Rayleigh scattering calibration were selected at the following solar zenith angle of 19–22° and wind speed of 5–13 m/s to reduce the reflection contributed by the water surface. The total Rayleigh scattering calibration uncertainties of visible bands are 2.44% (blue), 3.86% (green), and 4.63% (red) respectively. Compared with the recent field calibration results, the errors are −1.69% (blue), 1.83% (green), and −0.79% (red). Therefore, the Rayleigh scattering calibration can become an operational in-flight calibration method for the high spatial resolution satellites. Full article

► Figures

Open AccessArticle INS/GNSS Integration for Aerobatic Flight Applications and Aircraft Motion Surveying

by Edgar L. v. Hinüber, Christian Reimer, Tim Schneider and Michael Stock

Sensors 2017, 17(5), 941; doi:10.3390/s17050941

Received: 17 November 2016 / Revised: 14 April 2017 / Accepted: 21 April 2017 / Published: 26 April 2017

Viewed by 407 | PDF Full-text (10381 KB) | HTML Full-text | XML Full-text

Abstract

This paper presents field tests of challenging flight applications obtained with a new family of lightweight low-power INS/GNSS (inertial navigation system/global satellite navigation system) solutions based on MEMS (micro-electro-mechanical- sensor) machined sensors, being used for UAV (unmanned aerial

[...] Read more.

This paper presents field tests of challenging flight applications obtained with a new family of lightweight low-power INS/GNSS (inertial navigation system/global satellite navigation system) solutions based on MEMS (micro-electro-mechanical- sensor) machined sensors, being used for UAV (unmanned aerial vehicle) navigation and control as well as for aircraft motion dynamics analysis and trajectory surveying. One key is a 42+ state extended Kalman-filter-based powerful data fusion, which also allows the estimation and correction of parameters that are typically affected by sensor aging, especially when applying MEMS-based inertial sensors, and which is not yet deeply considered in the literature. The paper presents the general system architecture, which allows iMAR Navigation the integration of all classes of inertial sensors and GNSS (global navigation satellite system) receivers from very-low-cost MEMS and high performance MEMS over FOG (fiber optical gyro) and RLG (ring laser gyro) up to HRG (hemispherical resonator gyro) technology, and presents detailed flight test results obtained under extreme flight conditions. As a real-world example, the aerobatic maneuvers of the World Champion 2016 (Red Bull Air Race) are presented. Short consideration is also given to surveying applications, where the ultimate performance of the same data fusion, but applied on gravimetric surveying, is discussed. Full article

(This article belongs to the Special Issue Inertial Sensors and Systems 2016)

► Figures

Figure 1

Open AccessArticle Robust In-Flight Sensor Fault Diagnostics for Aircraft Engine Based on Sliding Mode Observers

by Xiaodong Chang, Jinquan Huang and Feng Lu

Sensors 2017, 17(4), 835; doi:10.3390/s17040835

Received: 12 March 2017 / Revised: 5 April 2017 / Accepted: 7 April 2017 / Published: 11 April 2017

Viewed by 363 | PDF Full-text (2452 KB) | HTML Full-text | XML Full-text

Abstract

For a sensor fault diagnostic system of aircraft engines, the health performance degradation is an inevitable interference that cannot be neglected. To address this issue, this paper investigates an integrated on-line sensor fault diagnostic scheme for a commercial aircraft engine based on a

[...] Read more.

For a sensor fault diagnostic system of aircraft engines, the health performance degradation is an inevitable interference that cannot be neglected. To address this issue, this paper investigates an integrated on-line sensor fault diagnostic scheme for a commercial aircraft engine based on a sliding mode observer (SMO). In this approach, one sliding mode observer is designed for engine health performance tracking, and another for sensor fault reconstruction. Both observers are employed in in-flight applications. The results of the former SMO are analyzed for post-flight updating the baseline model of the latter. This idea is practical and feasible since the updating process does not require the algorithm to be regulated or redesigned, so that ground-based intervention is avoided, and the update process is implemented in an economical and efficient way. With this setup, the robustness of the proposed scheme to the health degradation is much enhanced and the latter SMO is able to fulfill sensor fault reconstruction over the course of the engine life. The proposed sensor fault diagnostic system is applied to a nonlinear simulation of a commercial aircraft engine, and its effectiveness is evaluated in several fault scenarios. Full article

(This article belongs to the Section Physical Sensors)

► Figures

Figure 1

Open AccessTechnical Note Perpetual Solar-Powered Flight across Regions around the World for a Year-Long Operation

by Parvathy Rajendran, Muhammad Hazim Masral and Hairuniza Ahmed Kutty

Aerospace 2017, 4(2), 20; doi:10.3390/aerospace4020020

Received: 16 January 2017 / Revised: 4 April 2017 / Accepted: 7 April 2017 / Published: 11 April 2017

Viewed by 763 | PDF Full-text (849 KB) | HTML Full-text | XML Full-text

Abstract

This study aims to promote the conventional solar-powered unmanned aerial vehicle (UAV) to be used as a satellite known as a pseudo-satellite (pseudolite). The applications of UAV as a satellite are still in the initial stages because these proposed UAVs are required to

[...] Read more.

This study aims to promote the conventional solar-powered unmanned aerial vehicle (UAV) to be used as a satellite known as a pseudo-satellite (pseudolite). The applications of UAV as a satellite are still in the initial stages because these proposed UAVs are required to fly for long hours at a specified altitude. Any solar-powered system requires extensive mission operation planning to ensure sufficient power to sustain a level flight. This study simulates the optimal UAV configurations at various global locations, and determines the feasibility of a solar-powered UAV to sustain a continuous mission. This study is divided into two different phases. An all-year operation of the average UAV (AVUAV) is simulated in Phase One and is designed specifically for each of 12 cities, namely, Ottawa, Honolulu, Quito, Tahiti, Brasilia, London, Riyadh, Tokyo, Kuala Lumpur, Accra, Port Louis, and Suva. Phase Two is a simulation of a solar-powered UAV design model known as 1UAV, applicable to any city around the world for a year-long flight. The findings state that a single UAV design is sufficient to operate continuously around the world if its detailed mission path planning has been defined. Full article

(This article belongs to the collection Unmanned Aerial Systems)

► Figures

Figure 1

Open AccessArticle Local Observability Analysis of Star Sensor Installation Errors in a SINS/CNS Integration System for Near-Earth Flight Vehicles

by Yanqiang Yang, Chunxi Zhang and Jiazhen Lu

Sensors 2017, 17(1), 167; doi:10.3390/s17010167

Received: 25 September 2016 / Revised: 9 January 2017 / Accepted: 12 January 2017 / Published: 16 January 2017

Viewed by 522 | PDF Full-text (1377 KB) | HTML Full-text | XML Full-text

Abstract

Strapdown inertial navigation system/celestial navigation system (SINS/CNS) integrated navigation is a fully autonomous and high precision method, which has been widely used to improve the hitting accuracy and quick reaction capability of near-Earth flight vehicles. The installation errors between SINS and star sensors

[...] Read more.

Strapdown inertial navigation system/celestial navigation system (SINS/CNS) integrated navigation is a fully autonomous and high precision method, which has been widely used to improve the hitting accuracy and quick reaction capability of near-Earth flight vehicles. The installation errors between SINS and star sensors have been one of the main factors that restrict the actual accuracy of SINS/CNS. In this paper, an integration algorithm based on the star vector observations is derived considering the star sensor installation error. Then, the star sensor installation error is accurately estimated based on Kalman Filtering (KF). Meanwhile, a local observability analysis is performed on the rank of observability matrix obtained via linearization observation equation, and the observable conditions are presented and validated. The number of star vectors should be greater than or equal to 2, and the times of posture adjustment also should be greater than or equal to 2. Simulations indicate that the star sensor installation error could be readily observable based on the maneuvering condition; moreover, the attitude errors of SINS are less than 7 arc-seconds. This analysis method and conclusion are useful in the ballistic trajectory design of near-Earth flight vehicles. Full article

(This article belongs to the Section Physical Sensors)

► Figures

Figure 1

Open AccessArticle High Accuracy Acquisition of 3-D Flight Trajectory of Individual Insect Based on Phase Measurement

by Cheng Hu, Yunkai Deng, Rui Wang, Changjiang Liu and Teng Long

Sensors 2016, 16(12), 2166; doi:10.3390/s16122166

Received: 1 September 2016 / Revised: 14 November 2016 / Accepted: 13 December 2016 / Published: 17 December 2016

Viewed by 458 | PDF Full-text (3000 KB) | HTML Full-text | XML Full-text

Abstract

Accurate acquisition of 3-D flight trajectory of individual insect could be of benefit to the research of insect migration behaviors and the development of migratory entomology. This paper proposes a novel method to acquire 3-D flight trajectory of individual insect. First, based on

[...] Read more.

Accurate acquisition of 3-D flight trajectory of individual insect could be of benefit to the research of insect migration behaviors and the development of migratory entomology. This paper proposes a novel method to acquire 3-D flight trajectory of individual insect. First, based on the high range resolution synthesizing and the Doppler coherent processing, insects can be detected effectively, and the range resolution and velocity resolution are combined together to discriminate insects. Then, high accuracy range measurement with the carrier phase is proposed. The range measurement accuracy can reach millimeter level and benefits the acquisition of 3-D trajectory information significantly. Finally, based on the multi-baselines interferometry theory, the azimuth and elevation angles can be obtained with high accuracy. Simulation results prove that the retrieval accuracy of a simulated target’s 3-D coordinates can reach centimeter level. Experiments utilizing S-band radar in an anechoic chamber were taken and results showed that the insects’ flight behaviors and 3-D coordinates’ variation matched the practical cases well. In conclusion, both the simulated and experimental datasets validate the feasibility of the proposed method, which could be a novel measurement way of monitoring flight trajectory of aerial free-fly insects. Full article

(This article belongs to the Section Remote Sensors)

► Figures

Figure 1

Open AccessArticle An Algorithm for In-Flight Spectral Calibration of Imaging Spectrometers

by Gerrit Kuhlmann, Andreas Hueni, Alexander Damm and Dominik Brunner

Remote Sens. 2016, 8(12), 1017; doi:10.3390/rs8121017

Received: 5 October 2016 / Revised: 15 November 2016 / Accepted: 5 December 2016 / Published: 11 December 2016

Abstract

Accurate spectral calibration of satellite and airborne spectrometers is essential for remote sensing applications that rely on accurate knowledge of center wavelength (CW) positions and slit function parameters (SFP). We present a new in-flight spectral calibration algorithm that retrieves CWs and SFPs across

[...] Read more.

Accurate spectral calibration of satellite and airborne spectrometers is essential for remote sensing applications that rely on accurate knowledge of center wavelength (CW) positions and slit function parameters (SFP). We present a new in-flight spectral calibration algorithm that retrieves CWs and SFPs across a wide spectral range by fitting a high-resolution solar spectrum and atmospheric absorbers to in-flight radiance spectra. Using a maximum a posteriori optimal estimation approach, the quality of the fit can be improved with a priori information. The algorithm was tested with synthetic spectra and applied to data from the APEX imaging spectrometer over the spectral range of 385–870 nm. CWs were retrieved with high accuracy (uncertainty <0.05 spectral pixels) from Fraunhofer lines below 550 nm and atmospheric absorbers above 650 nm. This enabled a detailed characterization of APEX’s across-track spectral smile and a previously unknown along-track drift. The FWHMs of the slit function were also retrieved with good accuracy (<10% uncertainty) for synthetic spectra, while some obvious misfits appear for the APEX spectra that are likely related to radiometric calibration issues. In conclusion, our algorithm significantly improves the in-flight spectral calibration of APEX and similar spectrometers, making them better suited for the retrieval of atmospheric and surface variables relying on accurate calibration. Full article

(This article belongs to the Special Issue Uncertainties in Remote Sensing)

► Figures

Open AccessArticle Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method

by Mingzhang Luo, Weijie Li, Chuang Hei and Gangbing Song

Sensors 2016, 16(12), 2083; doi:10.3390/s16122083

Received: 3 November 2016 / Revised: 1 December 2016 / Accepted: 6 December 2016 / Published: 7 December 2016

Cited by 1 | Viewed by 518 | PDF Full-text (5057 KB) | HTML Full-text | XML Full-text

Abstract

Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting,

[...] Read more.

Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs. Full article

(This article belongs to the Section Physical Sensors)

► Figures

Figure 1

Open AccessArticle Wing Geometry and Kinematic Parameters Optimization of Flapping Wing Hovering Flight

by Xijun Ke and Weiping Zhang

Appl. Sci. 2016, 6(12), 390; doi:10.3390/app6120390

Received: 8 October 2016 / Revised: 10 November 2016 / Accepted: 23 November 2016 / Published: 29 November 2016

Viewed by 608 | PDF Full-text (5910 KB) | HTML Full-text | XML Full-text | Supplementary Files

Abstract

How to efficiently mimic the wing shape and kinematics pattern of an able hovering living flier is always a concern of researchers from the flapping wing micro aerial vehicles community. In this work, the separate or combined optimizations of wing geometry or/and wing

[...] Read more.

How to efficiently mimic the wing shape and kinematics pattern of an able hovering living flier is always a concern of researchers from the flapping wing micro aerial vehicles community. In this work, the separate or combined optimizations of wing geometry or/and wing kinematic parameters are systematically performed to minimize the energy of hovering flight, firstly on the basis of analytically extended quasi-steady aerodynamic model by using hybrid genetic algorithm. Before the elaboration of the optimization problem, the parametrization description of dynamically scaled wing with non-dimensional conformal feature of insect-scale rigid wing is firstly proposed. The optimization results show that the combined optimization of wing geometry and kinematic parameters can obtain lower flapping frequency, larger wing geometry parameters and lower power density in comparison with those from other cases of optimization. Moreover, the flapping angle for the optimization involving wing kinematic parameters manifests harmonic shape profile and the pitch angle possesses round trapezoidal profile with certain faster time scale of pitch reversal. The combined optimization framework provides a novel method for the conceptual design of fundamental parameters of biomimetic flapping wing micro aerial vehicle. Full article

► Figures

Figure 1

Open AccessArticle Using Landsat, MODIS, and a Biophysical Model to Evaluate LST in Urban Centers

by Mohammad Z. Al-Hamdan, Dale A. Quattrochi, Lahouari Bounoua, Asia Lachir and Ping Zhang

Remote Sens. 2016, 8(11), 952; doi:10.3390/rs8110952

Received: 13 August 2016 / Revised: 23 September 2016 / Accepted: 19 October 2016 / Published: 16 November 2016

Viewed by 801 | PDF Full-text (8288 KB) | HTML Full-text | XML Full-text

Abstract

In this paper, we assessed and compared land surface temperature (LST) in urban centers using data from Landsat, MODIS, and the Simple Biosphere model (SiB2). We also evaluated the sensitivity of the model’s LST to different land cover types, fractions (percentages), and emissivities

[...] Read more.

In this paper, we assessed and compared land surface temperature (LST) in urban centers using data from Landsat, MODIS, and the Simple Biosphere model (SiB2). We also evaluated the sensitivity of the model’s LST to different land cover types, fractions (percentages), and emissivities compared to reference points derived from Landsat thermal data. This was demonstrated in three climatologically- and morphologically-different cities of Atlanta, GA, New York, NY, and Washington, DC. Our results showed that in these cities SiB2 was sensitive to both the emissivity and the land cover type and fraction, but much more sensitive to the latter. The practical implications of these results are rather significant since they imply that the SiB2 model can be used to run different scenarios for evaluating urban heat island (UHI) mitigation strategies. This study also showed that using detailed emissivities per land cover type and fractions from Landsat-derived data caused a convergence of the model results towards the Landsat-derived LST for most of the studied cases. This study also showed that SiB2 LSTs are closer in magnitude to Landsat-derived LSTs than MODIS-derived LSTs. It is important, however, to emphasize that both Landsat and MODIS LSTs are not direct observations and, as such, do not represent a ground truth. More studies will be needed to compare these results to in situ LST data and provide further validation. Full article

(This article belongs to the Special Issue Multi-Sensor and Multi-Data Integration in Remote Sensing)

► Figures

Open AccessArticle Modelling of XCO₂ Surfaces Based on Flight Tests of TanSat Instruments

by Li Li Zhang, Tian Xiang Yue, John P. Wilson, Ding Yi Wang, Na Zhao, Yu Liu, Dong Dong Liu, Zheng Ping Du, Yi Fu Wang, Chao Lin, Yu Quan Zheng and Jian Hong Guo

Sensors 2016, 16(11), 1818; doi:10.3390/s16111818

Received: 16 August 2016 / Revised: 25 October 2016 / Accepted: 26 October 2016 / Published: 1 November 2016

Cited by 1 | Viewed by 666 | PDF Full-text (5005 KB) | HTML Full-text | XML Full-text

Abstract

The TanSat carbon satellite is to be launched at the end of 2016. In order to verify the performance of its instruments, a flight test of TanSat instruments was conducted in Jilin Province in September, 2015. The flight test area covered a total

[...] Read more.

The TanSat carbon satellite is to be launched at the end of 2016. In order to verify the performance of its instruments, a flight test of TanSat instruments was conducted in Jilin Province in September, 2015. The flight test area covered a total area of about 11,000 km² and the underlying surface cover included several lakes, forest land, grassland, wetland, farmland, a thermal power plant and numerous cities and villages. We modeled the column-average dry-air mole fraction of atmospheric carbon dioxide (XCO₂) surface based on flight test data which measured the near- and short-wave infrared (NIR) reflected solar radiation in the absorption bands at around 760 and 1610 nm. However, it is difficult to directly analyze the spatial distribution of XCO₂ in the flight area using the limited flight test data and the approximate surface of XCO₂, which was obtained by regression modeling, which is not very accurate either. We therefore used the high accuracy surface modeling (HASM) platform to fill the gaps where there is no information on XCO₂ in the flight test area, which takes the approximate surface of XCO₂ as its driving field and the XCO₂ observations retrieved from the flight test as its optimum control constraints. High accuracy surfaces of XCO₂ were constructed with HASM based on the flight’s observations. The results showed that the mean XCO₂ in the flight test area is about 400 ppm and that XCO₂ over urban areas is much higher than in other places. Compared with OCO-2’s XCO₂, the mean difference is 0.7 ppm and the standard deviation is 0.95 ppm. Therefore, the modelling of the XCO₂ surface based on the flight test of the TanSat instruments fell within an expected and acceptable range. Full article

(This article belongs to the Section Remote Sensors)

► Figures

Figure 1

Open AccessArticle Exploring the Magnetic Field Configuration in BL Lac Using GMVA

by Bindu Rani, Thomas Krichbaum, Jeff A. Hodgson, Shoko Koyama, Anton J. Zensus, Lars Fuhramnn, Alan Marscher and Svetlana Jorstad

Galaxies 2016, 4(3), 32; doi:10.3390/galaxies4030032

Received: 15 July 2016 / Revised: 9 September 2016 / Accepted: 13 September 2016 / Published: 20 September 2016

Viewed by 496 | PDF Full-text (1612 KB) | HTML Full-text | XML Full-text

Abstract

The high radio frequency polarization imaging of non-thermal emission from active galactic nuclei (AGN) is a direct way to probe the magnetic field strength and structure in the immediate vicinity of supermassive black holes (SMBHs) and is crucial in testing the jet-launching scenario.

[...] Read more.

The high radio frequency polarization imaging of non-thermal emission from active galactic nuclei (AGN) is a direct way to probe the magnetic field strength and structure in the immediate vicinity of supermassive black holes (SMBHs) and is crucial in testing the jet-launching scenario. To explore the the magnetic field configuration at the base of jets in blazars, we took advantage of the full polarization capabilities of the Global Millimeter VLBI Array (GMVA). With an angular resolution of ∼50 micro-arcseconds (μas) at 86 GHz, one could resolve scales up to ∼450 gravitational radii (for a

10^{9}

solar mass black hole at a redshift of 0.1). We present here the preliminary results of our study on the blazar BL Lac. Our results suggest that on sub-mas scales the core and the central jet of BL Lac are significantly polarized with two distinct regions of polarized intensity. We also noted a great morphological similarity between the 7 mm/3 mm VLBI images at very similar angular resolution. Full article

(This article belongs to the Special Issue Blazars through Sharp Multi-wavelength Eyes)

► Figures

Figure 1

Open AccessArticle Analysis of MABEL Bathymetry in Keweenaw Bay and Implications for ICESat-2 ATLAS

by Nicholas A. Forfinski-Sarkozi and Christopher E. Parrish

Remote Sens. 2016, 8(9), 772; doi:10.3390/rs8090772

Received: 3 August 2016 / Revised: 4 September 2016 / Accepted: 14 September 2016 / Published: 19 September 2016

Viewed by 600 | PDF Full-text (7255 KB) | HTML Full-text | XML Full-text

Abstract

In 2018, the National Aeronautics and Space Administration (NASA) is scheduled to launch the Ice, Cloud, and land Elevation Satellite-2 (ICESat-2), with a new six-beam, green-wavelength, photon-counting lidar system, Advanced Topographic Laser Altimeter System (ATLAS). The primary objectives of the ICESat-2 mission are

[...] Read more.

In 2018, the National Aeronautics and Space Administration (NASA) is scheduled to launch the Ice, Cloud, and land Elevation Satellite-2 (ICESat-2), with a new six-beam, green-wavelength, photon-counting lidar system, Advanced Topographic Laser Altimeter System (ATLAS). The primary objectives of the ICESat-2 mission are to measure ice-sheet elevations, sea-ice thickness, and global biomass. However, if bathymetry can be reliably retrieved from ATLAS data, this could assist in addressing a key data need in many coastal and inland water body areas, including areas that are poorly-mapped and/or difficult to access. Additionally, ATLAS-derived bathymetry could be used to constrain bathymetry derived from complementary data, such as passive, multispectral imagery and synthetic aperture radar (SAR). As an important first step in evaluating the ability to map bathymetry from ATLAS, this study involves a detailed assessment of bathymetry from the Multiple Altimeter Beam Experimental Lidar (MABEL), NASA’s airborne ICESat-2 simulator, flown on the Earth Resources 2 (ER-2) high-altitude aircraft. An interactive, web interface, MABEL Viewer, was developed and used to identify bottom returns in Keweenaw Bay, Lake Superior. After applying corrections for refraction and channel-specific elevation biases, MABEL bathymetry was compared against National Oceanic and Atmospheric Administration (NOAA) data acquired two years earlier. The results indicate that MABEL reliably detected bathymetry in depths of up to 8 m, with a root mean square (RMS) difference of 0.7 m, with respect to the reference data. Additionally, a version of the lidar equation was developed for predicting bottom-return signal levels in MABEL and tested using the Keweenaw Bay data. Future work will entail extending these results to ATLAS, as the technical specifications of the sensor become available. Full article

► Figures

Open AccessArticle Comparison of the Average Lift Coefficient ͞C_L and Normalized Lift ͞η_L for Evaluating Hovering and Forward Flapping Flight

by Phillip Burgers

Aerospace 2016, 3(3), 24; doi:10.3390/aerospace3030024

Received: 3 June 2016 / Revised: 19 July 2016 / Accepted: 19 July 2016 / Published: 29 July 2016

Cited by 1 | Viewed by 1208 | PDF Full-text (1145 KB) | HTML Full-text | XML Full-text

Abstract

The capability of flapping wings to generate lift is currently evaluated by using the lift coefficient

{\bar{C}}_{L}

, a dimensionless number that is derived from the basal equation that calculates the steady-state lift coefficient C_L for fixed wings. In contrast

[...] Read more.

The capability of flapping wings to generate lift is currently evaluated by using the lift coefficient

{\bar{C}}_{L}

, a dimensionless number that is derived from the basal equation that calculates the steady-state lift coefficient C_L for fixed wings. In contrast to its simple and direct application to fixed wings, the equation for

{\bar{C}}_{L}

requires prior knowledge of the flow field along the wing span, which results in two integrations: along the wing span and over time. This paper proposes an alternate average normalized lift

{\bar{η}}_{L}

that is easy to apply to hovering and forward flapping flight, does not require prior knowledge of the flow field, does not resort to calculus for its solution, and its lineage is close to the basal equation for steady state C_L. Furthermore, the average normalized lift

{\bar{η}}_{L}

converges to the legacy C_L as the flapping frequency is reduced to zero (gliding flight). Its ease of use is illustrated by applying the average normalized lift

{\bar{η}}_{L}

to the hovering and translating flapping flight of bumblebees. This application of the normalized lift is compared to the same application using two widely-accepted legacy average lift coefficients: the first

{\bar{C}}_{L}

as defined by Dudley and Ellington, and the second lift coefficient by Weis-Fogh. Furthermore, it is shown that the average normalized lift

{\bar{η}}_{L}

has a physical meaning: that of the ratio of work exerted by the flapping wings onto the surrounding flow field and the kinetic energy available at the aerodynamic surfaces during the generation of lift. The working equation for the average normalized lift

{\bar{η}}_{L}

is derived and is presented as a function of Strouhal number, St. Full article

(This article belongs to the Special Issue Flapping Wings)

► Figures

Open AccessArticle Calibration and Validation of Landsat Tree Cover in the Taiga−Tundra Ecotone

by Paul Mannix Montesano, Christopher S. R. Neigh, Joseph Sexton, Min Feng, Saurabh Channan, Kenneth J. Ranson and John R. Townshend

Remote Sens. 2016, 8(7), 551; doi:10.3390/rs8070551

Received: 25 March 2016 / Revised: 10 June 2016 / Accepted: 22 June 2016 / Published: 29 June 2016

Cited by 3 | Viewed by 731 | PDF Full-text (4337 KB) | HTML Full-text | XML Full-text

Abstract

Monitoring current forest characteristics in the taiga−tundra ecotone (TTE) at multiple scales is critical for understanding its vulnerability to structural changes. A 30 m spatial resolution Landsat-based tree canopy cover map has been calibrated and validated in the TTE with reference tree cover

[...] Read more.

Monitoring current forest characteristics in the taiga−tundra ecotone (TTE) at multiple scales is critical for understanding its vulnerability to structural changes. A 30 m spatial resolution Landsat-based tree canopy cover map has been calibrated and validated in the TTE with reference tree cover data from airborne LiDAR and high resolution spaceborne images across the full range of boreal forest tree cover. This domain-specific calibration model used estimates of forest height to determine reference forest cover that best matched Landsat estimates. The model removed the systematic under-estimation of tree canopy cover >80% and indicated that Landsat estimates of tree canopy cover more closely matched canopies at least 2 m in height rather than 5 m. The validation improved estimates of uncertainty in tree canopy cover in discontinuous TTE forests for three temporal epochs (2000, 2005, and 2010) by reducing systematic errors, leading to increases in tree canopy cover uncertainty. Average pixel-level uncertainties in tree canopy cover were 29.0%, 27.1% and 31.1% for the 2000, 2005 and 2010 epochs, respectively. Maps from these calibrated data improve the uncertainty associated with Landsat tree canopy cover estimates in the discontinuous forests of the circumpolar TTE. Full article

(This article belongs to the Special Issue Validation and Inter-Comparison of Land Cover and Land Use Data)

► Figures

Open AccessArticle Large Scale Applications Using FBG Sensors: Determination of In-Flight Loads and Shape of a Composite Aircraft Wing

by Matthew J. Nicolas, Rani W. Sullivan and W. Lance Richards

Aerospace 2016, 3(3), 18; doi:10.3390/aerospace3030018

Received: 16 May 2016 / Revised: 7 June 2016 / Accepted: 8 June 2016 / Published: 23 June 2016

Cited by 1 | Viewed by 1350 | PDF Full-text (2849 KB) | HTML Full-text | XML Full-text

Abstract

Technological advances have enabled the development of a number of optical fiber sensing methods over the last few years. The most prevalent optical technique involves the use of fiber Bragg grating (FBG) sensors. These small, lightweight sensors have many attributes that enable their

[...] Read more.

Technological advances have enabled the development of a number of optical fiber sensing methods over the last few years. The most prevalent optical technique involves the use of fiber Bragg grating (FBG) sensors. These small, lightweight sensors have many attributes that enable their use for a number of measurement applications. Although much literature is available regarding the use of FBGs for laboratory level testing, few publications in the public domain exist of their use at the operational level. Therefore, this paper gives an overview of the implementation of FBG sensors for large scale structures and applications. For demonstration, a case study is presented in which FBGs were used to determine the deflected wing shape and the out-of-plane loads of a 5.5-m carbon-composite wing of an ultralight aerial vehicle. The in-plane strains from the 780 FBG sensors were used to obtain the out-of-plane loads as well as the wing shape at various load levels. The calculated out-of-plane displacements and loads were within 4.2% of the measured data. This study demonstrates a practical method in which direct measurements are used to obtain critical parameters from the high distribution of FBG sensors. This procedure can be used to obtain information for structural health monitoring applications to quantify healthy vs. unhealthy structures. Full article

(This article belongs to the Special Issue Adaptive/Smart Structures and Multifunctional Materials 2016)

► Figures

Open AccessArticle Wildfires Dynamics in Siberian Larch Forests

by Evgenii I. Ponomarev, Viacheslav I. Kharuk and Kenneth J. Ranson

Forests 2016, 7(6), 125; doi:10.3390/f7060125

Received: 29 February 2016 / Revised: 5 June 2016 / Accepted: 8 June 2016 / Published: 17 June 2016

Cited by 3 | Viewed by 919 | PDF Full-text (2432 KB) | HTML Full-text | XML Full-text

Abstract

Wildfire number and burned area temporal dynamics within all of Siberia and along a south-north transect in central Siberia (45°–73° N) were studied based on NOAA/AVHRR (National Oceanic and Atmospheric Administration/ Advanced Very High Resolution Radiometer) and Terra/MODIS (Moderate Resolution Imaging Spectroradiometer) data

[...] Read more.

Wildfire number and burned area temporal dynamics within all of Siberia and along a south-north transect in central Siberia (45°–73° N) were studied based on NOAA/AVHRR (National Oceanic and Atmospheric Administration/ Advanced Very High Resolution Radiometer) and Terra/MODIS (Moderate Resolution Imaging Spectroradiometer) data and field measurements for the period 1996–2015. In addition, fire return interval (FRI) along the south-north transect was analyzed. Both the number of forest fires and the size of the burned area increased during recent decades (p < 0.05). Significant correlations were found between forest fires, burned areas and air temperature (r = 0.5) and drought index (The Standardized Precipitation Evapotranspiration Index, SPEI) (r = −0.43). Within larch stands along the transect, wildfire frequency was strongly correlated with incoming solar radiation (r = 0.91). Fire danger period length decreased linearly from south to north along the transect. Fire return interval increased from 80 years at 62° N to 200 years at the Arctic Circle (66°33’ N), and to about 300 years near the northern limit of closed forest stands (about 71°+ N). That increase was negatively correlated with incoming solar radiation (r = −0.95). Full article

(This article belongs to the Special Issue Fire Regimes: Spatial and Temporal Variability and Their Effects on Forests) Printed Edition available

Open AccessArticle First in-Flight Radiometric Calibration of MUX and WFI on-Board CBERS-4

by Cibele Pinto, Flávio Ponzoni, Ruy Castro, Larry Leigh, Nischal Mishra, David Aaron and Dennis Helder

Remote Sens. 2016, 8(5), 405; doi:10.3390/rs8050405

Received: 3 February 2016 / Revised: 5 April 2016 / Accepted: 5 May 2016 / Published: 11 May 2016

Cited by 1 | Viewed by 717 | PDF Full-text (4225 KB) | HTML Full-text | XML Full-text

Abstract

Brazil and China have a long-term joint space based sensor program called China-Brazil Earth Resources Satellite (CBERS). The most recent satellite of this program (CBERS-4) was successfully launched on 7 December 2014. This work describes a complete procedure, along with the associated uncertainties,

[...] Read more.

Brazil and China have a long-term joint space based sensor program called China-Brazil Earth Resources Satellite (CBERS). The most recent satellite of this program (CBERS-4) was successfully launched on 7 December 2014. This work describes a complete procedure, along with the associated uncertainties, used to calculate the in-flight absolute calibration coefficients for the sensors Multispectral Camera (MUX) and Wide-Field Imager (WFI) on-board CBERS-4. Two absolute radiometric calibration techniques were applied: (i) reflectance-based approach and (ii) cross-calibration method. A specific site at Algodones Dunes region located in the southwestern portion of the United States of America was used as a reference surface. Radiometric ground and atmospheric measurements were carried out on 9 March 2015, when CBERS-4 passed over the region. In addition, a cross-calibration between both MUX and WFI on-board CBERS-4 and the Operational Land Imager (OLI) on-board Landsat-8 was performed using the Libya-4 Pseudo Invariant Calibration Site. The gain coefficients are now available: 1.68, 1.62, 1.59 and 1.42 for MUX and 0.379, 0.498, 0.360 and 0.351 for WFI spectral bands blue, green, red and NIR, respectively, in units of (W/(m²·sr·μm))/DN. These coefficients were determined with uncertainties lower than 3.5%. As a validation of these radiometric coefficients, cross-calibration was also undertaken. An evaluation of radiometric consistency was performed between the two instruments (MUX and WFI) on-board CBERS-4 and with the well calibrated Landsat-7 ETM+. Results show that the reflectance values match in all the analogous spectral bands within the specified calibration uncertainties. Full article

► Figures

Open AccessArticle Design of a Computerised Flight Mill Device to Measure the Flight Potential of Different Insects

by Antonio Martí-Campoy, Juan Antonio Ávalos, Antonia Soto, Francisco Rodríguez-Ballester, Victoria Martínez-Blay and Manuel Pérez Malumbres

Sensors 2016, 16(4), 485; doi:10.3390/s16040485

Received: 8 January 2016 / Revised: 22 March 2016 / Accepted: 30 March 2016 / Published: 7 April 2016

Viewed by 763 | PDF Full-text (17214 KB) | HTML Full-text | XML Full-text

Abstract

Several insect species pose a serious threat to different plant species, sometimes becoming a pest that produces significant damage to the landscape, biodiversity, and/or the economy. This is the case of Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae), Semanotus laurasii Lucas (Coleoptera: Cerambycidae), and Monochamus

[...] Read more.

Several insect species pose a serious threat to different plant species, sometimes becoming a pest that produces significant damage to the landscape, biodiversity, and/or the economy. This is the case of Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae), Semanotus laurasii Lucas (Coleoptera: Cerambycidae), and Monochamus galloprovincialis Olivier (Coleoptera: Cerambycidae), which have become serious threats to ornamental and productive trees all over the world such as palm trees, cypresses, and pines. Knowledge about their flight potential is very important for designing and applying measures targeted to reduce the negative effects from these pests. Studying the flight capability and behaviour of some insects is difficult due to their small size and the large area wherein they can fly, so we wondered how we could obtain information about their flight capabilities in a controlled environment. The answer came with the design of flight mills. Relevant data about the flight potential of these insects may be recorded and analysed by means of a flight mill. Once an insect is attached to the flight mill, it is able to fly in a circular direction without hitting walls or objects. By adding sensors to the flight mill, it is possible to record the number of revolutions and flight time. This paper presents a full description of a computer monitored flight mill. The description covers both the mechanical and the electronic parts in detail. The mill was designed to easily adapt to the anatomy of different insects and was successfully tested with individuals from three species R. ferrugineus, S. laurasii, and M. galloprovincialis. Full article

(This article belongs to the Special Issue State-of-the-Art Sensors Technology in Spain 2015) Printed Edition available

► Figures

Open AccessArticle Magnesium and Space Flight

by Scott M. Smith and Sara R. Zwart

Nutrients 2015, 7(12), 10209-10222; doi:10.3390/nu7125528

Received: 9 October 2015 / Revised: 30 November 2015 / Accepted: 2 December 2015 / Published: 8 December 2015

Abstract

Magnesium is an essential nutrient for muscle, cardiovascular, and bone health on Earth, and during space flight. We sought to evaluate magnesium status in 43 astronauts (34 male, 9 female; 47 ± 5 years old, mean ± SD) before, during, and after 4–6-month

[...] Read more.

Magnesium is an essential nutrient for muscle, cardiovascular, and bone health on Earth, and during space flight. We sought to evaluate magnesium status in 43 astronauts (34 male, 9 female; 47 ± 5 years old, mean ± SD) before, during, and after 4–6-month space missions. We also studied individuals participating in a ground analog of space flight (head-down-tilt bed rest; n = 27 (17 male, 10 female), 35 ± 7 years old). We evaluated serum concentration and 24-h urinary excretion of magnesium, along with estimates of tissue magnesium status from sublingual cells. Serum magnesium increased late in flight, while urinary magnesium excretion was higher over the course of 180-day space missions. Urinary magnesium increased during flight but decreased significantly at landing. Neither serum nor urinary magnesium changed during bed rest. For flight and bed rest, significant correlations existed between the area under the curve of serum and urinary magnesium and the change in total body bone mineral content. Tissue magnesium concentration was unchanged after flight and bed rest. Increased excretion of magnesium is likely partially from bone and partially from diet, but importantly, it does not come at the expense of muscle tissue stores. While further study is needed to better understand the implications of these findings for longer space exploration missions, magnesium homeostasis and tissue status seem well maintained during 4–6-month space missions. Full article

Open AccessArticle Assessing Optimal Flight Parameters for Generating Accurate Multispectral Orthomosaicks by UAV to Support Site-Specific Crop Management

by Francisco-Javier Mesas-Carrascosa, Jorge Torres-Sánchez, Inmaculada Clavero-Rumbao, Alfonso García-Ferrer, Jose-Manuel Peña, Irene Borra-Serrano and Francisca López-Granados

Remote Sens. 2015, 7(10), 12793-12814; doi:10.3390/rs71012793

Received: 17 June 2015 / Revised: 22 August 2015 / Accepted: 21 September 2015 / Published: 29 September 2015

Cited by 8 | Viewed by 1362 | PDF Full-text (3632 KB) | HTML Full-text | XML Full-text

Abstract

This article describes the technical specifications and configuration of a multirotor unmanned aerial vehicle (UAV) to acquire remote images using a six-band multispectral sensor. Several flight missions were programmed as follows: three flight altitudes (60, 80 and 100 m), two flight modes (stop

[...] Read more.

This article describes the technical specifications and configuration of a multirotor unmanned aerial vehicle (UAV) to acquire remote images using a six-band multispectral sensor. Several flight missions were programmed as follows: three flight altitudes (60, 80 and 100 m), two flight modes (stop and cruising modes) and two ground control point (GCP) settings were considered to analyze the influence of these parameters on the spatial resolution and spectral discrimination of multispectral orthomosaicked images obtained using Pix4Dmapper. Moreover, it is also necessary to consider the area to be covered or the flight duration according to any flight mission programmed. The effect of the combination of all these parameters on the spatial resolution and spectral discrimination of the orthomosaicks is presented. Spectral discrimination has been evaluated for a specific agronomical purpose: to use the UAV remote images for the detection of bare soil and vegetation (crop and weeds) for in-season site-specific weed management. These results show that a balance between spatial resolution and spectral discrimination is needed to optimize the mission planning and image processing to achieve every agronomic objective. In this way, users do not have to sacrifice flying at low altitudes to cover the whole area of interest completely. Full article

(This article belongs to the Special Issue Remote Sensing in Precision Agriculture)

► Figures

Open AccessReview The Flight of Birds and Other Animals

by Colin J. Pennycuick

Aerospace 2015, 2(3), 505-523; doi:10.3390/aerospace2030505

Received: 9 July 2015 / Revised: 24 August 2015 / Accepted: 26 August 2015 / Published: 1 September 2015

Viewed by 1672 | PDF Full-text (6550 KB) | HTML Full-text | XML Full-text

Abstract

Methods of observing birds in flight now include training them to fly under known conditions in wind tunnels, and fitting free-flying birds with data loggers, that are either retrieved or read remotely via satellite links. The performance that comes to light depends on

[...] Read more.

Methods of observing birds in flight now include training them to fly under known conditions in wind tunnels, and fitting free-flying birds with data loggers, that are either retrieved or read remotely via satellite links. The performance that comes to light depends on the known limitations of the materials from which they are made, and the conditions in which the birds live. Bird glide polars can be obtained by training birds to glide in a tilting wind tunnel. Translating these curves to power required from the flight muscles in level flight requires drag coefficients to be measured, which unfortunately does not work with bird bodies, because the flow is always fully detached. The drag of bodies in level flight can be determined by observing wingbeat frequency, and shows C_D values around 0.08 in small birds, down to 0.06 in small waders specialised for efficient migration. Lift coefficients are up to 1.6 in gliding, or 1.8 for short, temporary glides. In-flight measurements can be used to calculate power curves for birds in level flight, and this has been applied to migrating geese in detail. These typically achieve lift:drag ratios around 15, including allowances for stops, as against 19 for continuous powered flight. The same calculations, applied to Pacific Black-tailed Godwits which start with fat fractions up to 0.55 at departure, show that such birds not only cross the Pacific to New Zealand, but have enough fuel in hand to reach the South Pole if that were necessary. This performance depends on the “dual fuel” arrangements of these migrants, whereby they use fat as their main fuel, and supplement this by extra fuel from burning the engine (flight muscles), as less power is needed later in the flight. The accuracy of these power curves has never been checked, although provision for stopping the bird, and making these checks at regular intervals during a simulated flight was built into the original design of the Lund wind tunnel. The Flight programme, which does these comparisons, also had provision for including contributions due to extracting energy from the atmosphere (soaring), or intermittent bounding flight in small birds (Passerines). It has been known for some time that the feathered surface allows the bird to delay or reverse detachment of the boundary layer, although exactly how this works remains a mystery, which might have practical applications. The bird wing was in use in past times, when birds were still competing with pterosaurs, although these had less efficient wings. The birds that survived the extinction that killed the pterosaurs and dinosaurs have (today) an automatic spherical navigator, which enables them to cross the Pacific and find New Zealand on the other side. Bats have never had such a device, and pterosaurs probably did not either. Animals, when seen from a zoological point of view, are adapted to whatever problems they had to deal with in earlier times. Full article

(This article belongs to the collection Feature Papers in Aerospace)

► Figures

Open AccessArticle Clear Skies and Grey Areas: Flight Attendants’ Secondhand Smoke Exposure and Attitudes toward Smoke-Free Policy 25 Years since Smoking was Banned on Airplanes

by Frances A. Stillman, Andrea Soong, Laura Y. Zheng and Ana Navas-Acien

Int. J. Environ. Res. Public Health 2015, 12(6), 6378-6387; doi:10.3390/ijerph120606378

Received: 21 April 2015 / Revised: 26 May 2015 / Accepted: 1 June 2015 / Published: 4 June 2015

Cited by 2 | Viewed by 1328 | PDF Full-text (320 KB) | HTML Full-text | XML Full-text

Abstract

Our objective was to provide descriptive data on flight attendant secondhand smoke (SHS) exposure in the work environment, and to examine attitudes toward SHS exposure, personal health, and smoke-free policy in the workplace and public places. Flight attendants completed a web-based survey of

[...] Read more.

Our objective was to provide descriptive data on flight attendant secondhand smoke (SHS) exposure in the work environment, and to examine attitudes toward SHS exposure, personal health, and smoke-free policy in the workplace and public places. Flight attendants completed a web-based survey of self-reported SHS exposure and air quality in the work environment. We assessed the frequency and duration of SHS exposure in distinct areas of the workplace, attitudes toward SHS exposure and its health effects, and attitudes toward smoke-free policy in the workplace as well as general public places. A total of 723 flight attendants participated in the survey, and 591 responded to all survey questions. The mean level of exposure per flight attendant over the past month was 249 min. The majority of participants reported being exposed to SHS always/often in outdoor areas of an airport (57.7%). Participants who worked before the in-flight smoking ban (n = 240) were more likely to support further smoking policies in airports compared to participants who were employed after the ban (n = 346) (76.7% versus 60.4%, p-value < 0.01). Flight attendants are still being exposed to SHS in the workplace, sometimes at concerning levels during the non-flight portions of their travel. Flight attendants favor smoke-free policies and want to see further restrictions in airports and public places. Full article

Open AccessArticle Mapping Species Composition of Forests and Tree Plantations in Northeastern Costa Rica with an Integration of Hyperspectral and Multitemporal Landsat Imagery

by Matthew E. Fagan, Ruth S. DeFries, Steven E. Sesnie, J. Pablo Arroyo-Mora, Carlomagno Soto, Aditya Singh, Philip A. Townsend and Robin L. Chazdon

Remote Sens. 2015, 7(5), 5660-5696; doi:10.3390/rs70505660

Received: 14 February 2015 / Accepted: 14 April 2015 / Published: 5 May 2015

Cited by 11 | Viewed by 2737 | PDF Full-text (3495 KB) | HTML Full-text | XML Full-text

Abstract

An efficient means to map tree plantations is needed to detect tropical land use change and evaluate reforestation projects. To analyze recent tree plantation expansion in northeastern Costa Rica, we examined the potential of combining moderate-resolution hyperspectral imagery (2005 HyMap mosaic) with multitemporal,

[...] Read more.

An efficient means to map tree plantations is needed to detect tropical land use change and evaluate reforestation projects. To analyze recent tree plantation expansion in northeastern Costa Rica, we examined the potential of combining moderate-resolution hyperspectral imagery (2005 HyMap mosaic) with multitemporal, multispectral data (Landsat) to accurately classify (1) general forest types and (2) tree plantations by species composition. Following a linear discriminant analysis to reduce data dimensionality, we compared four Random Forest classification models: hyperspectral data (HD) alone; HD plus interannual spectral metrics; HD plus a multitemporal forest regrowth classification; and all three models combined. The fourth, combined model achieved overall accuracy of 88.5%. Adding multitemporal data significantly improved classification accuracy (p < 0.0001) of all forest types, although the effect on tree plantation accuracy was modest. The hyperspectral data alone classified six species of tree plantations with 75% to 93% producer’s accuracy; adding multitemporal spectral data increased accuracy only for two species with dense canopies. Non-native tree species had higher classification accuracy overall and made up the majority of tree plantations in this landscape. Our results indicate that combining occasionally acquired hyperspectral data with widely available multitemporal satellite imagery enhances mapping and monitoring of reforestation in tropical landscapes. Full article

(This article belongs to the Special Issue Mapping the Dynamics of Forest Plantations in Tropical and Subtropical Regions from Multi-Source Remote Sensing)

► Figures

Open AccessArticle Trajectory Management of the Unmanned Aircraft System (UAS) in Emergency Situation

by Andrzej Majka

Aerospace 2015, 2(2), 222-234; doi:10.3390/aerospace2020222

Received: 1 February 2015 / Revised: 13 March 2015 / Accepted: 18 March 2015 / Published: 4 May 2015

Cited by 2 | Viewed by 2605 | PDF Full-text (1378 KB) | HTML Full-text | XML Full-text

Abstract

Unmanned aircraft must be characterized by a level of safety, similar to that of manned aircraft, when performing flights over densely populated areas. Dangerous situations or emergencies are frequently connected with the necessity to change the profiles and parameters of a flight as

[...] Read more.

Unmanned aircraft must be characterized by a level of safety, similar to that of manned aircraft, when performing flights over densely populated areas. Dangerous situations or emergencies are frequently connected with the necessity to change the profiles and parameters of a flight as well as the flight plans. The aim of this work is to present the methods used to determine an Unmanned Aircraft System’s (UAS) flight profile after a dangerous situation or emergency occurs. The analysis was limited to the possibility of an engine system emergency and further flight continuing along a trajectory of which the shape depends on the type of the emergency. The suggested method also enables the determination of an optimal flying trajectory, based on the territory of a special protection zone (for example, large populated areas), in the case of an emergency that would disable continuation of the performed task. The method used in this work allows researchers, in a simplified way, to solve a variation task using the Ritz–Galerkin method, consisting of an approximate solution of the boundary value problem to determine the optimal flight path. The worked out method can become an element of the on-board system supporting UAS flight control. Full article

(This article belongs to the Special Issue Unmanned Aerial Systems 2015)

► Figures

Open AccessArticle Development of Flight Path Planning for Multirotor Aerial Vehicles

by Yi-Ju Tsai, Chia-Sung Lee, Chun-Liang Lin and Ching-Huei Huang

Aerospace 2015, 2(2), 171-188; doi:10.3390/aerospace2020171

Received: 21 November 2014 / Revised: 11 March 2015 / Accepted: 24 March 2015 / Published: 27 April 2015

Cited by 1 | Viewed by 1803 | PDF Full-text (3915 KB) | HTML Full-text | XML Full-text

Abstract

This study addresses the flight-path planning problem for multirotor aerial vehicles (AVs). We consider the specific features and requirements of real-time flight-path planning and develop a rapidly-exploring random tree (RRT) algorithm to determine a preliminary flight path in three-dimensional space. Since the path

[...] Read more.

This study addresses the flight-path planning problem for multirotor aerial vehicles (AVs). We consider the specific features and requirements of real-time flight-path planning and develop a rapidly-exploring random tree (RRT) algorithm to determine a preliminary flight path in three-dimensional space. Since the path obtained by the RRT may not be optimal due to the existence of redundant waypoints. To reduce the cost of energy during AV’s flight, the excessive waypoints need to be refined. We revise the A-star algorithm by adopting the heading of the AV as the key indices while calculating the cost. Bezier curves are finally proposed to smooth the flight path, making it applicable for real-world flight. Full article

(This article belongs to the Special Issue Unmanned Aerial Systems 2015)

► Figures

Open AccessArticle Invariant Observer-Based State Estimation for Micro-Aerial Vehicles in GPS-Denied Indoor Environments Using an RGB-D Camera and MEMS Inertial Sensors

by Dachuan Li, Qing Li, Liangwen Tang, Sheng Yang, Nong Cheng and Jingyan Song

Micromachines 2015, 6(4), 487-522; doi:10.3390/mi6040487

Received: 27 December 2014 / Revised: 11 April 2015 / Accepted: 17 April 2015 / Published: 22 April 2015

Cited by 2 | Viewed by 1654 | PDF Full-text (2589 KB) | HTML Full-text | XML Full-text

Abstract

This paper presents a non-linear state observer-based integrated navigation scheme for estimating the attitude, position and velocity of micro aerial vehicles (MAV) operating in GPS-denied indoor environments, using the measurements from low-cost MEMS (micro electro-mechanical systems) inertial sensors and an RGB-D camera. A

[...] Read more.

This paper presents a non-linear state observer-based integrated navigation scheme for estimating the attitude, position and velocity of micro aerial vehicles (MAV) operating in GPS-denied indoor environments, using the measurements from low-cost MEMS (micro electro-mechanical systems) inertial sensors and an RGB-D camera. A robust RGB-D visual odometry (VO) approach was developed to estimate the MAV’s relative motion by extracting and matching features captured by the RGB-D camera from the environment. The state observer of the RGB-D visual-aided inertial navigation was then designed based on the invariant observer theory for systems possessing symmetries. The motion estimates from the RGB-D VO were fused with inertial and magnetic measurements from the onboard MEMS sensors via the state observer, providing the MAV with accurate estimates of its full six degree-of-freedom states. Implementations on a quadrotor MAV and indoor flight test results demonstrate that the resulting state observer is effective in estimating the MAV’s states without relying on external navigation aids such as GPS. The properties of computational efficiency and simplicity in gain tuning make the proposed invariant observer-based navigation scheme appealing for actual MAV applications in indoor environments. Full article

(This article belongs to the Special Issue Next Generation MEMS-Based Navigation—Systems and Applications)

► Figures

Open AccessArticle Broadband and High Sensitive Time-of-Flight Diffraction Ultrasonic Transducers Based on PMNT/Epoxy 1–3 Piezoelectric Composite

by Dongxu Liu, Qingwen Yue, Ji Deng, Di Lin, Xiaobing Li, Wenning Di, Xi'an Wang, Xiangyong Zhao and Haosu Luo

Sensors 2015, 15(3), 6807-6817; doi:10.3390/s150306807

Received: 4 January 2015 / Revised: 9 March 2015 / Accepted: 18 March 2015 / Published: 19 March 2015

Viewed by 1573 | PDF Full-text (1911 KB) | HTML Full-text | XML Full-text

Abstract

5–6 MHz PMNT/epoxy 1–3 composites were prepared by a modified dice-and-fill method. They exhibit excellent properties for ultrasonic transducer applications, such as ultrahigh thickness electromechanical coupling coefficient k_t (85.7%), large piezoelectric coefficient d₃₃ (1209 pC/N), and relatively low acoustic impedance Z

[...] Read more.

5–6 MHz PMNT/epoxy 1–3 composites were prepared by a modified dice-and-fill method. They exhibit excellent properties for ultrasonic transducer applications, such as ultrahigh thickness electromechanical coupling coefficient k_t (85.7%), large piezoelectric coefficient d₃₃ (1209 pC/N), and relatively low acoustic impedance Z (1.82 × 10⁷ kg/(m²·s)). Besides, two types of Time-of-Flight Diffraction (TOFD) ultrasonic transducers have been designed, fabricated, and characterized, which have different matching layer schemes with the acoustic impedance of 4.8 and 5.7 × 10⁶ kg/(m²·s), respectively. In the detection on a backwall of 12.7 mm polystyrene, the former exhibits higher detectivity, the relative pulse-echo sensitivity and −6 dB relative bandwidth are −21.93 dB and 102.7%, respectively, while the later exhibits broader bandwidth, the relative pulse-echo sensitivity and −6 dB relative bandwidth are −24.08 dB and 117.3%, respectively. These TOFD ultrasonic transducers based on PMNT/epoxy 1–3 composite exhibit considerably improved performance over the commercial PZT/epoxy 1–3 composite TOFD ultrasonic transducer. Full article

(This article belongs to the Special Issue Acoustic Waveguide Sensors)

Open AccessArticle Comparison of the Detection Characteristics of Trace Species Using Laser-Induced Breakdown Spectroscopy and Laser Breakdown Time-of-Flight Mass Spectrometry

by Zhenzhen Wang, Yoshihiro Deguchi, Junjie Yan and Jiping Liu

Sensors 2015, 15(3), 5982-6008; doi:10.3390/s150305982

Received: 16 December 2014 / Revised: 27 February 2015 / Accepted: 28 February 2015 / Published: 11 March 2015

Cited by 5 | Viewed by 1588 | PDF Full-text (3523 KB) | HTML Full-text | XML Full-text

Abstract

The rapid and precise element measurement of trace species, such as mercury, iodine, strontium, cesium, etc. is imperative for various applications, especially for industrial needs. The elements mercury and iodine were measured by two detection methods for comparison of the corresponding detection features.

[...] Read more.

The rapid and precise element measurement of trace species, such as mercury, iodine, strontium, cesium, etc. is imperative for various applications, especially for industrial needs. The elements mercury and iodine were measured by two detection methods for comparison of the corresponding detection features. A laser beam was focused to induce plasma. Emission and ion signals were detected using laser-induced breakdown spectroscopy (LIBS) and laser breakdown time-of-flight mass spectrometry (LB-TOFMS). Multi-photon ionization and electron impact ionization in the plasma generation process can be controlled by the pressure and pulse width. The effect of electron impact ionization on continuum emission, coexisting molecular and atomic emissions became weakened in low pressure condition. When the pressure was less than 1 Pa, the plasma was induced by laser dissociation and multi-photon ionization in LB-TOFMS. According to the experimental results, the detection limits of mercury and iodine in N₂ were 3.5 ppb and 60 ppb using low pressure LIBS. The mercury and iodine detection limits using LB-TOFMS were 1.2 ppb and 9.0 ppb, which were enhanced due to different detection features. The detection systems of LIBS and LB-TOFMS can be selected depending on the condition of each application. Full article

(This article belongs to the Special Issue Modern Technologies for Sensing Pollution in Air, Water, and Soil)

Open AccessArticle Metabolites Software-Assisted Flavonoid Hunting in Plants Using Ultra-High Performance Liquid Chromatography-Quadrupole-Time of Flight Mass Spectrometry

by Wan-Yi Gu, Na Li, Elaine Lai-Han Leung, Hua Zhou, Guo-An Luo, Liang Liu and Jian-Lin Wu

Molecules 2015, 20(3), 3955-3971; doi:10.3390/molecules20033955

Received: 31 January 2015 / Revised: 17 February 2015 / Accepted: 25 February 2015 / Published: 2 March 2015

Abstract

Plant secondary metabolism drives the generation of metabolites used for host plant resistance, as biopesticides and botanicals, even for the discovery of new therapeutics for human diseases. Flavonoids are one of the largest and most studied classes of specialized plant metabolites. To quickly

[...] Read more.

Plant secondary metabolism drives the generation of metabolites used for host plant resistance, as biopesticides and botanicals, even for the discovery of new therapeutics for human diseases. Flavonoids are one of the largest and most studied classes of specialized plant metabolites. To quickly identify the potential bioactive flavonoids in herbs, a metabolites software-assisted flavonoid hunting approach was developed, which mainly included three steps: firstly, utilizing commercial metabolite software, a flavonoids database was established based on the biosynthetic pathways; secondly, mass spectral data of components in herbs were acquired by ultra-high performance liquid chromatography-quadrupole-time of flight mass spectrometry (UHPLC-Q-TOF-MS); and finally, the acquired LC-MS data were imported into the database and the compounds in the herbs were automatically identified by comparison of their mass spectra with the theoretical values. As a case study, the flavonoids in Smilax glabra were profiled using this approach. As a result, 104 flavonoids including 27 potential new compounds were identified. To our knowledge, this is the first report on profiling the components in the plants utilizing the plant metabolic principles with the assistance of metabolites software. This approach can be extended to the analysis of flavonoids in other plants. Full article

(This article belongs to the Section Natural Products)

Open AccessArticle Sampling-Based Real-Time Motion Planning under State Uncertainty for Autonomous Micro-Aerial Vehicles in GPS-Denied Environments

by Dachuan Li, Qing Li, Nong Cheng and Jingyan Song

Sensors 2014, 14(11), 21791-21825; doi:10.3390/s141121791

Received: 31 July 2014 / Revised: 26 October 2014 / Accepted: 3 November 2014 / Published: 18 November 2014

Cited by 1 | Viewed by 1473 | PDF Full-text (6232 KB) | HTML Full-text | XML Full-text

Abstract

This paper presents a real-time motion planning approach for autonomous vehicles with complex dynamics and state uncertainty. The approach is motivated by the motion planning problem for autonomous vehicles navigating in GPS-denied dynamic environments, which involves non-linear and/or non-holonomic vehicle dynamics, incomplete state

[...] Read more.

This paper presents a real-time motion planning approach for autonomous vehicles with complex dynamics and state uncertainty. The approach is motivated by the motion planning problem for autonomous vehicles navigating in GPS-denied dynamic environments, which involves non-linear and/or non-holonomic vehicle dynamics, incomplete state estimates, and constraints imposed by uncertain and cluttered environments. To address the above motion planning problem, we propose an extension of the closed-loop rapid belief trees, the closed-loop random belief trees (CL-RBT), which incorporates predictions of the position estimation uncertainty, using a factored form of the covariance provided by the Kalman filter-based estimator. The proposed motion planner operates by incrementally constructing a tree of dynamically feasible trajectories using the closed-loop prediction, while selecting candidate paths with low uncertainty using efficient covariance update and propagation. The algorithm can operate in real-time, continuously providing the controller with feasible paths for execution, enabling the vehicle to account for dynamic and uncertain environments. Simulation results demonstrate that the proposed approach can generate feasible trajectories that reduce the state estimation uncertainty, while handling complex vehicle dynamics and environment constraints. Full article

(This article belongs to the Special Issue Positioning and Tracking Sensors and Technologies in Road Transport)

Open AccessArticle In-Flight Estimation of Center of Gravity Position Using All-Accelerometers

by Yazan Mohammad Al-Rawashdeh, Moustafa Elshafei and Mohammad Fahad Al-Malki

Sensors 2014, 14(9), 17567-17585; doi:10.3390/s140917567

Received: 4 June 2014 / Revised: 2 September 2014 / Accepted: 2 September 2014 / Published: 19 September 2014

Cited by 4 | Viewed by 1689 | PDF Full-text (2248 KB) | HTML Full-text | XML Full-text

Abstract

Changing the position of the Center of Gravity (CoG) for an aerial vehicle is a challenging part in navigation, and control of such vehicles. In this paper, an all-accelerometers-based inertial measurement unit is presented, with a proposed method for on-line estimation of the

[...] Read more.

Changing the position of the Center of Gravity (CoG) for an aerial vehicle is a challenging part in navigation, and control of such vehicles. In this paper, an all-accelerometers-based inertial measurement unit is presented, with a proposed method for on-line estimation of the position of the CoG. The accelerometers’ readings are used to find and correct the vehicle’s angular velocity and acceleration using an Extended Kalman Filter. Next, the accelerometers’ readings along with the estimated angular velocity and acceleration are used in an identification scheme to estimate the position of the CoG and the vehicle’s linear acceleration. The estimated position of the CoG and motion measurements can then be used to update the control rules to achieve better trim conditions for the air vehicle. Full article

(This article belongs to the Section Physical Sensors)

► Figures

Open AccessArticle CO Self-Shielding as a Mechanism to Make ¹⁶O-Enriched Solids in the Solar Nebula

by Joseph A. Nuth, III, Natasha M. Johnson and Hugh G. M. Hill

Challenges 2014, 5(1), 152-158; doi:10.3390/challe5010152

Received: 1 April 2014 / Revised: 8 May 2014 / Accepted: 13 May 2014 / Published: 21 May 2014

Cited by 2 | Viewed by 1964 | PDF Full-text (160 KB) | HTML Full-text | XML Full-text

Abstract

Photochemical self-shielding of CO has been proposed as a mechanism to produce solids observed in the modern, ¹⁶O-depleted solar system. This is distinct from the relatively ¹⁶O-enriched composition of the solar nebula, as demonstrated by the oxygen isotopic composition of the

[...] Read more.

Photochemical self-shielding of CO has been proposed as a mechanism to produce solids observed in the modern, ¹⁶O-depleted solar system. This is distinct from the relatively ¹⁶O-enriched composition of the solar nebula, as demonstrated by the oxygen isotopic composition of the contemporary sun. While supporting the idea that self-shielding can produce local enhancements in ¹⁶O-depleted solids, we argue that complementary enhancements of ¹⁶O-enriched solids can also be produced via C¹⁶O-based, Fischer-Tropsch type (FTT) catalytic processes that could produce much of the carbonaceous feedstock incorporated into accreting planetesimals. Local enhancements could explain observed ¹⁶O enrichment in calcium-aluminum-rich inclusions (CAIs), such as those from the meteorite, Isheyevo (CH/CHb), as well as in chondrules from the meteorite, Acfer 214 (CH3). CO self-shielding results in an overall increase in the ¹⁷O and ¹⁸O content of nebular solids only to the extent that there is a net loss of C¹⁶O from the solar nebula. In contrast, if C¹⁶O reacts in the nebula to produce organics and water then the net effect of the self-shielding process will be negligible for the average oxygen isotopic content of nebular solids and other mechanisms must be sought to produce the observed dichotomy between oxygen in the Sun and that in meteorites and the terrestrial planets. This illustrates that the formation and metamorphism of rocks and organics need to be considered in tandem rather than as isolated reaction networks. Full article

(This article belongs to the Special Issue Challenges in Astrobiology)

Open AccessArticle Effect of Olfactory Stimulus on the Flight Course of a Honeybee, Apis mellifera, in a Wind Tunnel

by Hidetoshi Ikeno, Tadaaki Akamatsu, Yuji Hasegawa and Hiroyuki Ai

Insects 2014, 5(1), 92-104; doi:10.3390/insects5010092

Received: 31 October 2013 / Revised: 21 December 2013 / Accepted: 24 December 2013 / Published: 31 December 2013

Cited by 1 | Viewed by 1794 | PDF Full-text (898 KB) | HTML Full-text | XML Full-text

Abstract

It is known that the honeybee, Apis mellifera, uses olfactory stimulus as important information for orienting to food sources. Several studies on olfactory-induced orientation flight have been conducted in wind tunnels and in the field. From these studies, optical sensing is used

[...] Read more.

It is known that the honeybee, Apis mellifera, uses olfactory stimulus as important information for orienting to food sources. Several studies on olfactory-induced orientation flight have been conducted in wind tunnels and in the field. From these studies, optical sensing is used as the main information with the addition of olfactory signals and the navigational course followed by these sensory information. However, it is not clear how olfactory information is reflected in the navigation of flight. In this study, we analyzed the detailed properties of flight when oriented to an odor source in a wind tunnel. We recorded flying bees with a video camera to analyze the flight area, speed, angular velocity and trajectory. After bees were trained to be attracted to a feeder, the flight trajectories with or without the olfactory stimulus located upwind of the feeder were compared. The results showed that honeybees flew back and forth in the proximity of the odor source, and the search range corresponded approximately to the odor spread area. It was also shown that the angular velocity was different inside and outside the odor spread area, and trajectories tended to be bent or curved just outside the area. Full article

(This article belongs to the Special Issue Honey Bee Behavior)

Open AccessArticle Accurate Estimation of Airborne Ultrasonic Time-of-Flight for Overlapping Echoes

by Esther G. Sarabia, Jose R. Llata, Sandra Robla, Carlos Torre-Ferrero and Juan P. Oria

Sensors 2013, 13(11), 15465-15488; doi:10.3390/s131115465

Received: 17 October 2013 / Revised: 5 November 2013 / Accepted: 7 November 2013 / Published: 12 November 2013

Cited by 4 | Viewed by 1685 | PDF Full-text (3381 KB) | HTML Full-text | XML Full-text

Abstract

In this work, an analysis of the transmission of ultrasonic signals generated by piezoelectric sensors for air applications is presented. Based on this analysis, an ultrasonic response model is obtained for its application to the recognition of objects and structured environments for navigation

[...] Read more.

In this work, an analysis of the transmission of ultrasonic signals generated by piezoelectric sensors for air applications is presented. Based on this analysis, an ultrasonic response model is obtained for its application to the recognition of objects and structured environments for navigation by autonomous mobile robots. This model enables the analysis of the ultrasonic response that is generated using a pair of sensors in transmitter-receiver configuration using the pulse-echo technique. This is very interesting for recognizing surfaces that simultaneously generate a multiple echo response. This model takes into account the effect of the radiation pattern, the resonant frequency of the sensor, the number of cycles of the excitation pulse, the dynamics of the sensor and the attenuation with distance in the medium. This model has been developed, programmed and verified through a battery of experimental tests. Using this model a new procedure for obtaining accurate time of flight is proposed. This new method is compared with traditional ones, such as threshold or correlation, to highlight its advantages and drawbacks. Finally the advantages of this method are demonstrated for calculating multiple times of flight when the echo is formed by several overlapping echoes. Full article

(This article belongs to the Section Physical Sensors)

► Figures

Open AccessArticle Robust Flight Control Design to Minimize Aircraft Loss-of-Control Incidents

by Ronald A. Hess

Aerospace 2014, 1(1), 1-17; doi:10.3390/aerospace1010001

Received: 12 August 2013 / Revised: 25 September 2013 / Accepted: 16 October 2013 / Published: 7 November 2013

Cited by 1 | Viewed by 2887 | PDF Full-text (460 KB) | HTML Full-text | XML Full-text

Abstract

A pseudo-sliding mode control synthesis procedure discussed previously in the literature is applied to the design of a control system for a nonlinear model of the NASA Langley Generic Transport Model. The complete vehicle model is included as an appendix. The goal of

[...] Read more.

A pseudo-sliding mode control synthesis procedure discussed previously in the literature is applied to the design of a control system for a nonlinear model of the NASA Langley Generic Transport Model. The complete vehicle model is included as an appendix. The goal of the design effort is the synthesis of a robust control system to minimize aircraft loss-of-control by preserving fundamental pilot input—system response characteristics across the flight envelope, here including the possibility of actuator damage. The design is carried out completely in the frequency domain and is described by a ten-step synthesis procedure, also previously introduced it the literature. Five different flight tasks are considered in computer simulations of the completed design demonstrating the stability and performance robustness of the control system. Full article

(This article belongs to the Special Issue Driving Forward Aerospace Innovation)

Open AccessArticle Evaluating and Quantifying the Climate-Driven Interannual Variability in Global Inventory Modeling and Mapping Studies (GIMMS) Normalized Difference Vegetation Index (NDVI3g) at Global Scales

by Fan-Wei Zeng, G. James Collatz, Jorge E. Pinzon and Alvaro Ivanoff

Remote Sens. 2013, 5(8), 3918-3950; doi:10.3390/rs5083918

Received: 24 May 2013 / Revised: 23 July 2013 / Accepted: 23 July 2013 / Published: 8 August 2013

Abstract

Satellite observations of surface reflected solar radiation contain information about variability in the absorption of solar radiation by vegetation. Understanding the causes of variability is important for models that use these data to drive land surface fluxes or for benchmarking prognostic vegetation models.

[...] Read more.

Satellite observations of surface reflected solar radiation contain information about variability in the absorption of solar radiation by vegetation. Understanding the causes of variability is important for models that use these data to drive land surface fluxes or for benchmarking prognostic vegetation models. Here we evaluated the interannual variability in the new 30.5-year long global satellite-derived surface reflectance index data, Global Inventory Modeling and Mapping Studies normalized difference vegetation index (GIMMS NDVI3g). Pearson’s correlation and multiple linear stepwise regression analyses were applied to quantify the NDVI interannual variability driven by climate anomalies, and to evaluate the effects of potential interference (snow, aerosols and clouds) on the NDVI signal. We found ecologically plausible strong controls on NDVI variability by antecedent precipitation and current monthly temperature with distinct spatial patterns. Precipitation correlations were strongest for temperate to tropical water limited herbaceous systems where in some regions and seasons > 40% of the NDVI variance could be explained by precipitation anomalies. Temperature correlations were strongest in northern mid- to high-latitudes in the spring and early summer where up to 70% of the NDVI variance was explained by temperature anomalies. We find that, in western and central North America, winter-spring precipitation determines early summer growth while more recent precipitation controls NDVI variability in late summer. In contrast, current or prior wet season precipitation anomalies were correlated with all months of NDVI in sub-tropical herbaceous vegetation. Snow, aerosols and clouds as well as unexplained phenomena still account for part of the NDVI variance despite corrections. Nevertheless, this study demonstrates that GIMMS NDVI3g represents real responses of vegetation to climate variability that are useful for global models. Full article

(This article belongs to the Special Issue Monitoring Global Vegetation with AVHRR NDVI3g Data (1981-2011))

Open AccessArticle Linking Climate to Incidence of Zoonotic Cutaneous Leishmaniasis (L. major) in Pre-Saharan North Africa

by Lahouari Bounoua, Kholoud Kahime, Leila Houti, Tara Blakey, Kristie L. Ebi, Ping Zhang, Marc L. Imhoff, Kurtis J. Thome, Claire Dudek, Salah A. Sahabi, Mohammed Messouli, Baghdad Makhlouf, Abderrahmane El. Laamrani and Ali Boumezzough

Int. J. Environ. Res. Public Health 2013, 10(8), 3172-3191; doi:10.3390/ijerph10083172

Received: 3 May 2013 / Revised: 12 July 2013 / Accepted: 13 July 2013 / Published: 31 July 2013

Cited by 15 | Viewed by 2417 | PDF Full-text (550 KB) | HTML Full-text | XML Full-text

Abstract

Shifts in surface climate may have changed the dynamic of zoonotic cutaneous leishmaniasis (ZCL) in the pre-Saharan zones of North Africa. Caused by Leishmania major, this form multiplies in the body of rodents serving as reservoirs of the disease. The parasite is

[...] Read more.

Shifts in surface climate may have changed the dynamic of zoonotic cutaneous leishmaniasis (ZCL) in the pre-Saharan zones of North Africa. Caused by Leishmania major, this form multiplies in the body of rodents serving as reservoirs of the disease. The parasite is then transmitted to human hosts by the bite of a Phlebotomine sand fly (Diptera: Psychodidae) that was previously fed by biting an infected reservoir. We examine the seasonal and interannual dynamics of the incidence of this ZCL as a function of surface climate indicators in two regions covering a large area of the semi-arid Pre-Saharan North Africa. Results suggest that in this area, changes in climate may have initiated a trophic cascade that resulted in an increase in ZCL incidence. We find the correlation between the rainy season precipitation and the same year Normalized Difference Vegetation Index (NDVI) to be strong for both regions while the number of cases of ZCL incidence lags the precipitation and NDVI by 2 years. The zoonotic cutaneous leishmaniasis seasonal dynamic appears to be controlled by minimum temperatures and presents a 2-month lag between the reported infection date and the presumed date when the infection actually occurred. The decadal increase in the number of ZCL occurrence in the region suggests that changes in climate increased minimum temperatures sufficiently and created conditions suitable for endemicity that did not previously exist. We also find that temperatures above a critical range suppress ZCL incidence by limiting the vector’s reproductive activity. Full article

Open AccessArticle Influence of Age and Nutritional Status on Flight Performance of the Asian Tiger Mosquito Aedes albopictus (Diptera: Culicidae)

by Christian Kaufmann, Lauren F. Collins and Mark R. Brown

Insects 2013, 4(3), 404-412; doi:10.3390/insects4030404

Received: 11 April 2013 / Revised: 4 June 2013 / Accepted: 25 June 2013 / Published: 26 July 2013

Cited by 2 | Viewed by 1833 | PDF Full-text (272 KB) | HTML Full-text | XML Full-text

Abstract

The Asian tiger mosquito, Aedes albopictus, is a competent vector for arboviruses and recently was implicated as the vector of the first autochthonous cases of dengue and chikungunya in southern Europe. The objective of this study was to analyze the flight performance

[...] Read more.

The Asian tiger mosquito, Aedes albopictus, is a competent vector for arboviruses and recently was implicated as the vector of the first autochthonous cases of dengue and chikungunya in southern Europe. The objective of this study was to analyze the flight performance of female Ae. albopictus of different ages that were starved, sugar-fed, or sugar-fed and blood-fed, using flight mills. After three days of starvation post emergence, females flew an average distance of 0.7 ± 0.5 km in 1.9 ± 1.5 h during a 16 h trial period, whereas sugar- or sugar- and blood-fed females of this age covered a significantly higher distance of around 3 km with a mean total flight time of around 6 h. The age of females (up to four weeks) had no effect on performance. The average of maximal continuous flight segments of sugar-fed (2.14 ± 0.69 h) and blood-fed (3.17 ± 0.82 h) females was distinctly higher than of starved females (0.38 ± 0.15 h) of which most flyers (83%) performed maximal flight segments that lasted no longer than 0.5 h. Overall, the results for the laboratory monitored flight performance of Ae. albopictus confirm their ability to disperse a few kilometres between breeding site and host. Full article

(This article belongs to the Special Issue Feature Papers 2013)

Open AccessArticle Characterization of Canopy Layering in Forested Ecosystems Using Full Waveform Lidar

by Amanda S. Whitehurst, Anu Swatantran, J. Bryan Blair, Michelle A. Hofton and Ralph Dubayah

Remote Sens. 2013, 5(4), 2014-2036; doi:10.3390/rs5042014

Received: 20 February 2013 / Revised: 12 April 2013 / Accepted: 12 April 2013 / Published: 22 April 2013

Cited by 18 | Viewed by 2439 | PDF Full-text (1638 KB) | HTML Full-text | XML Full-text

Abstract

Canopy structure, the vertical distribution of canopy material, is an important element of forest ecosystem dynamics and habitat preference. Although vertical stratification, or “canopy layering,” is a basic characterization of canopy structure for research and forest management, it is difficult to quantify at

[...] Read more.

Canopy structure, the vertical distribution of canopy material, is an important element of forest ecosystem dynamics and habitat preference. Although vertical stratification, or “canopy layering,” is a basic characterization of canopy structure for research and forest management, it is difficult to quantify at landscape scales. In this paper we describe canopy structure and develop methodologies to map forest vertical stratification in a mixed temperate forest using full-waveform lidar. Two definitions—one categorical and one continuous—are used to map canopy layering over Hubbard Brook Experimental Forest, New Hampshire with lidar data collected in 2009 by NASA’s Laser Vegetation Imaging Sensor (LVIS). The two resulting canopy layering datasets describe variation of canopy layering throughout the forest and show that layering varies with terrain elevation and canopy height. This information should provide increased understanding of vertical structure variability and aid habitat characterization and other forest management activities. Full article

Open AccessArticle Effects of Flight on Gene Expression and Aging in the Honey Bee Brain and Flight Muscle

by Joseph W. Margotta, Georgina E. Mancinelli, Azucena A. Benito, Andrew Ammons, Stephen P. Roberts and Michelle M. Elekonich

Insects 2013, 4(1), 9-30; doi:10.3390/insects4010009

Received: 10 September 2012 / Revised: 12 November 2012 / Accepted: 4 December 2012 / Published: 20 December 2012

Abstract

Honey bees move through a series of in-hive tasks (e.g., “nursing”) to outside tasks (e.g., “foraging”) that are coincident with physiological changes and higher levels of metabolic activity. Social context can cause worker bees to speed up or slow down this process, and

[...] Read more.

Honey bees move through a series of in-hive tasks (e.g., “nursing”) to outside tasks (e.g., “foraging”) that are coincident with physiological changes and higher levels of metabolic activity. Social context can cause worker bees to speed up or slow down this process, and foragers may revert back to their earlier in-hive tasks accompanied by reversion to earlier physiological states. To investigate the effects of flight, behavioral state and age on gene expression, we used whole-genome microarrays and real-time PCR. Brain tissue and flight muscle exhibited different patterns of expression during behavioral transitions, with expression patterns in the brain reflecting both age and behavior, and expression patterns in flight muscle being primarily determined by age. Our data suggest that the transition from behaviors requiring little to no flight (nursing) to those requiring prolonged flight bouts (foraging), rather than the amount of previous flight per se, has a major effect on gene expression. Following behavioral reversion there was a partial reversion in gene expression but some aspects of forager expression patterns, such as those for genes involved in immune function, remained. Combined with our real-time PCR data, these data suggest an epigenetic control and energy balance role in honey bee functional senescence. Full article

(This article belongs to the Special Issue Honey Bee)

Open AccessReview Space Flight Calcium: Implications for Astronaut Health, Spacecraft Operations, and Earth

by Scott M. Smith, Torin McCoy, Daniel Gazda, Jennifer L. L. Morgan, Martina Heer and Sara R. Zwart

Nutrients 2012, 4(12), 2047-2068; doi:10.3390/nu4122047

Received: 11 October 2012 / Revised: 13 November 2012 / Accepted: 10 December 2012 / Published: 18 December 2012

Cited by 12 | Viewed by 2672 | PDF Full-text (806 KB) | HTML Full-text | XML Full-text

Abstract

The space flight environment is known to induce bone loss and, subsequently, calcium loss. The longer the mission, generally the more bone and calcium are lost. This review provides a history of bone and calcium studies related to space flight and highlights issues

[...] Read more.

The space flight environment is known to induce bone loss and, subsequently, calcium loss. The longer the mission, generally the more bone and calcium are lost. This review provides a history of bone and calcium studies related to space flight and highlights issues related to calcium excretion that the space program must consider so that urine can be recycled. It also discusses a novel technique using natural stable isotopes of calcium that will be helpful in the future to determine calcium and bone balance during space flight. Full article

(This article belongs to the Special Issue Dietary Calcium)

Open AccessArticle Seasonal Flight, Optimal Timing and Efficacy of Selected Insecticides for Cabbage Maggot (Delia radicum L., Diptera: Anthomyiidae) Control

by Renata Bažok, Mirna Ceranić-Sertić, Jasminka Igrc Barčić, Josip Borošić, Antonela Kozina, Tomislav Kos, Darija Lemić and Maja Čačija

Insects 2012, 3(4), 1001-1027; doi:10.3390/insects3041001

Received: 17 July 2012 / Revised: 26 September 2012 / Accepted: 15 October 2012 / Published: 22 October 2012

Cited by 3 | Viewed by 1963 | PDF Full-text (1451 KB) | HTML Full-text | XML Full-text

Abstract

In order to describe seasonal flight activity of the cabbage maggot Delia radicum (L.) adults in relation to Julian days (JD), degree-day accumulations (DDA) and precipitation, flight dynamics were followed weekly with the use of yellow sticky traps (YST). Climatic data were collected

[...] Read more.

In order to describe seasonal flight activity of the cabbage maggot Delia radicum (L.) adults in relation to Julian days (JD), degree-day accumulations (DDA) and precipitation, flight dynamics were followed weekly with the use of yellow sticky traps (YST). Climatic data were collected and DDA were calculated using the lower developmental threshold of 4.3 °C. The efficacy of four insecticides applied either as standard foliar treatment or through dipping the seedlings before transplanting was determined. Seasonal flight activity during the cultivation season of a mid-early variety of white cabbage was correlated with DDA and JD and was characterized by having two peaks. The first peak occurred between 119 ± 7.5 JD and 125.5 ± 8 JD when DDA was 471.35 ± 74.97 °C. The second occurred between 172.8 ± 6.1 JD and 179.3 ± 6.7 JD when DDA was 1,217.28 ± 96.12 °C. The DDA, cumulative capture of flies and JD are suitable for predicting the timing of insecticide application. Spraying with insecticides should be applied when the cumulative capture of flies reaches 100 flies/YST and when DDA reaches 400 °C. If only one parameter reaches the threshold, additional visual surveys should be employed to establish the level of infestation. Insecticides were able to ensure only partial control. In the future, alternative control tactics which employ seed treatments and nonpesticide measures should be investigated in Croatia. Full article

(This article belongs to the Special Issue Pest Control and Management)

Open AccessArticle Investigation of Non-Enzymatic Glycosylation of Human Serum Albumin Using Ion Trap-Time of Flight Mass Spectrometry

by Xue Bai, Zhangjie Wang, Chengcai Huang, Zhe Wang and Lianli Chi

Molecules 2012, 17(8), 8782-8794; doi:10.3390/molecules17088782

Received: 4 June 2012 / Revised: 8 July 2012 / Accepted: 13 July 2012 / Published: 25 July 2012

Cited by 13 | Viewed by 2784 | PDF Full-text (772 KB) | Supplementary Files

Abstract

Non-enzymatic glycosylation or glycation involves covalent attachment of reducing sugar residues to proteins without enzyme participation. Glycation of glucose to human serum albumin in vivo is related to diabetes and many other diseases. We present an approach using liquid chromatography coupled to an

[...] Read more.

Non-enzymatic glycosylation or glycation involves covalent attachment of reducing sugar residues to proteins without enzyme participation. Glycation of glucose to human serum albumin in vivo is related to diabetes and many other diseases. We present an approach using liquid chromatography coupled to an electrospray ionization source of a hybrid ion trap-time of flight (IT-TOF-MS/MS) tandem mass spectrometer to identify the glycation sites on serum albumin from both a healthy person and a diabetic patient. The MetID software, which is commonly used for screening metabolites, is adapted for peptide fingerprinting based on both m/z values and isotopic distribution profiles. A total of 21 glycation sites from the healthy person and 16 glycation sites from the diabetic patient were identified successfully. We also demonstrate the use of matrix assisted laser desorption ionization-time of flight mass spectrometry to estimate the incorporation ratio of glucose to albumin during glycation. Results from this study show that the glycation in healthy person is more complicated than previously thought. Further analysis of incorporation ratio distribution may be necessary to accurately reflect the change of serum albumin glycation in diabetic patients. Full article

► Figures

Open AccessArticle Time of Flight Sensor with a Flow Parallel Wire

by Christof Gerhardy and Werner Karl Schomburg

Micromachines 2012, 3(2), 325-330; doi:10.3390/mi3020325

Received: 5 March 2012 / Revised: 5 April 2012 / Accepted: 18 April 2012 / Published: 26 April 2012

Viewed by 2032 | PDF Full-text (306 KB) | HTML Full-text | XML Full-text

Abstract

A time of flight sensor has been equipped with a sensing wire parallel to the flow direction (flow parallel wire, FPW). A heat pulse is generated with a coil in the flow channel. The FPW has a center tap allowing its upstream and

[...] Read more.

A time of flight sensor has been equipped with a sensing wire parallel to the flow direction (flow parallel wire, FPW). A heat pulse is generated with a coil in the flow channel. The FPW has a center tap allowing its upstream and downstream parts to join in a half bridge. When a heat pulse passes the FPW, a large output peak is generated. The time between heat pulse generation and recording the peak maximum is only marginally affected by the properties of the fluid. With a combination of two FPWs, a measuring range of approximately 0.01–0.5 m/s can be achieved. Full article

(This article belongs to the Special Issue Micro Flow Controllers)

Open AccessArticle Attitude Determination Using a MEMS-Based Flight Information Measurement Unit

by Der-Ming Ma, Jaw-Kuen Shiau, I.-Chiang Wang and Yu-Heng Lin

Sensors 2012, 12(1), 1-23; doi:10.3390/s120100001

Received: 6 December 2011 / Revised: 19 December 2011 / Accepted: 19 December 2011 / Published: 22 December 2011

Cited by 17 | Viewed by 3266 | PDF Full-text (1766 KB) | HTML Full-text | XML Full-text

Abstract

Obtaining precise attitude information is essential for aircraft navigation and control. This paper presents the results of the attitude determination using an in-house designed low-cost MEMS-based flight information measurement unit. This study proposes a quaternion-based extended Kalman filter to integrate the traditional quaternion

[...] Read more.

Obtaining precise attitude information is essential for aircraft navigation and control. This paper presents the results of the attitude determination using an in-house designed low-cost MEMS-based flight information measurement unit. This study proposes a quaternion-based extended Kalman filter to integrate the traditional quaternion and gravitational force decomposition methods for attitude determination algorithm. The proposed extended Kalman filter utilizes the evolution of the four elements in the quaternion method for attitude determination as the dynamic model, with the four elements as the states of the filter. The attitude angles obtained from the gravity computations and from the electronic magnetic sensors are regarded as the measurement of the filter. The immeasurable gravity accelerations are deduced from the outputs of the three axes accelerometers, the relative accelerations, and the accelerations due to body rotation. The constraint of the four elements of the quaternion method is treated as a perfect measurement and is integrated into the filter computation. Approximations of the time-varying noise variances of the measured signals are discussed and presented with details through Taylor series expansions. The algorithm is intuitive, easy to implement, and reliable for long-term high dynamic maneuvers. Moreover, a set of flight test data is utilized to demonstrate the success and practicality of the proposed algorithm and the filter design. Full article

(This article belongs to the Section Physical Sensors)

Open AccessArticle Integrated Flight Path Planning System and Flight Control System for Unmanned Helicopters

by Shau-Shiun Jan and Yu-Hsiang Lin

Sensors 2011, 11(8), 7502-7529; doi:10.3390/s110807502

Received: 13 June 2011 / Revised: 20 July 2011 / Accepted: 22 July 2011 / Published: 28 July 2011

Viewed by 3611 | PDF Full-text (6265 KB) | HTML Full-text | XML Full-text

Abstract

This paper focuses on the design of an integrated navigation and guidance system for unmanned helicopters. The integrated navigation system comprises two systems: the Flight Path Planning System (FPPS) and the Flight Control System (FCS). The FPPS finds the shortest flight path by

[...] Read more.

This paper focuses on the design of an integrated navigation and guidance system for unmanned helicopters. The integrated navigation system comprises two systems: the Flight Path Planning System (FPPS) and the Flight Control System (FCS). The FPPS finds the shortest flight path by the A-Star (A*) algorithm in an adaptive manner for different flight conditions, and the FPPS can add a forbidden zone to stop the unmanned helicopter from crossing over into dangerous areas. In this paper, the FPPS computation time is reduced by the multi-resolution scheme, and the flight path quality is improved by the path smoothing methods. Meanwhile, the FCS includes the fuzzy inference systems (FISs) based on the fuzzy logic. By using expert knowledge and experience to train the FIS, the controller can operate the unmanned helicopter without dynamic models. The integrated system of the FPPS and the FCS is aimed at providing navigation and guidance to the mission destination and it is implemented by coupling the flight simulation software, X-Plane, and the computing software, MATLAB. Simulations are performed and shown in real time three-dimensional animations. Finally, the integrated system is demonstrated to work successfully in controlling the unmanned helicopter to operate in various terrains of a digital elevation model (DEM). Full article

(This article belongs to the Section Physical Sensors)

Open AccessArticle Using the Surface Reflectance MODIS Terra Product to Estimate Turbidity in Tampa Bay, Florida

by Max J. Moreno-Madrinan, Mohammad Z. Al-Hamdan, Douglas L. Rickman and Frank E. Muller-Karger

Remote Sens. 2010, 2(12), 2713-2728; doi:10.3390/rs2122713

Received: 12 October 2010 / Revised: 22 November 2010 / Accepted: 30 November 2010 / Published: 7 December 2010

Cited by 19 | Viewed by 7076 | PDF Full-text (447 KB) | HTML Full-text | XML Full-text

Abstract

Turbidity is a commonly-used index of the factors that determine light penetration in the water column. Consistent estimation of turbidity is crucial to design environmental and restoration management plans, to predict fate of possible pollutants, and to estimate sedimentary fluxes into the ocean.

[...] Read more.

Turbidity is a commonly-used index of the factors that determine light penetration in the water column. Consistent estimation of turbidity is crucial to design environmental and restoration management plans, to predict fate of possible pollutants, and to estimate sedimentary fluxes into the ocean. Traditional methods monitoring fixed geographical locations at fixed intervals may not be representative of the mean water turbidity in estuaries between intervals, and can be expensive and time consuming. Although remote sensing offers a good solution to this limitation, it is still not widely used due in part to required complex processing of imagery. There are satellite-derived products, including the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra surface reflectance daily product (MOD09GQ) Band 1 (620–670 nm) which are now routinely available at 250 m spatial resolution and corrected for atmospheric effect. This study shows this product to be useful to estimate turbidity in Tampa Bay, Florida, after rainfall events (R² = 0.76, n = 34). Within Tampa Bay, Hillsborough Bay (HB) and Old Tampa Bay (OTB) presented higher turbidity compared to Middle Tampa Bay (MTB) and Lower Tampa Bay (LTB). Full article

(This article belongs to the Special Issue Remote Sensing in Coastal Ecosystem)

► Figures

Open AccessArticle The Rover Environmental Monitoring Station Ground Temperature Sensor: A Pyrometer for Measuring Ground Temperature on Mars

by Eduardo Sebastián, Carlos Armiens, Javier Gómez-Elvira, María P. Zorzano, Jesus Martinez-Frias, Blanca Esteban and Miguel Ramos

Sensors 2010, 10(10), 9211-9231; doi:10.3390/s101009211

Received: 27 August 2010 / Revised: 14 September 2010 / Accepted: 25 September 2010 / Published: 15 October 2010

Cited by 11 | Viewed by 6601 | PDF Full-text (820 KB) | HTML Full-text | XML Full-text

Abstract

We describe the parameters that drive the design and modeling of the Rover Environmental Monitoring Station (REMS) Ground Temperature Sensor (GTS), an instrument aboard NASA’s Mars Science Laboratory, and report preliminary test results. REMS GTS is a lightweight, low-power, and low cost pyrometer

[...] Read more.

We describe the parameters that drive the design and modeling of the Rover Environmental Monitoring Station (REMS) Ground Temperature Sensor (GTS), an instrument aboard NASA’s Mars Science Laboratory, and report preliminary test results. REMS GTS is a lightweight, low-power, and low cost pyrometer for measuring the Martian surface kinematic temperature. The sensor’s main feature is its innovative design, based on a simple mechanical structure with no moving parts. It includes an in-flight calibration system that permits sensor recalibration when sensor sensitivity has been degraded by deposition of dust over the optics. This paper provides the first results of a GTS engineering model working in a Martian-like, extreme environment. Full article

(This article belongs to the Section Chemical Sensors)

MDPI Contact

Advanced Search

Search Results

MDPI Contact

Advanced Search

Search Results

Years

Subjects

Journals

Article Types

Countries