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Special Issue "Instruments and Methods for Ocean Observation and Monitoring"

A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Ocean Remote Sensing".

Deadline for manuscript submissions: closed (31 March 2018)

Special Issue Editors

Guest Editor
Dr. Francesco Serafino

Institute of Biometeorology, Via Giovanni Caproni, 8, 50145 Firenze, Italy
Website | E-Mail
Phone: +39 0586839788
Interests: radar imaging; sea current estimation; X-band radar data analysis; bathymetry reconstruction
Guest Editor
Dr. Claudio Lugni

Marine Engineering Institute, National Research Council, Roma, Italy
Website | E-Mail
Phone: +39 0650299274
Interests: ocean engineering; violent wave-structure interactions; offshore wind; floating wave energy converters
Guest Editor
Prof. Maurizio Brocchini

DICEA, Università Politecnica delle Marche, Via Brecce Bianche 12, 60131 Ancona, Italy
E-Mail
Phone: +39 0712204522
Interests: nearshore; hydro-morphodynamics; shallow-water flows; analytical-numerical modeling

Special Issue Information

Dear Colleagues,

The sea is at the center of key economic activities, such as maritime transport, energy, mining, fishing and aquaculture, boating, coastal tourism, as well as more technological sectors such as marine biotechnology. The theme of “Blue growth” is increasingly central in the planning of funding within the international arena, this being a long-term strategy to support sustainable growth in the marine and maritime sectors, both in coastal and offshore environment. Such a strategy is rooted in the awareness that seas and oceans represent a driving force for the international economy, with enormous potential for technological innovation and sustainable growth. For those reasons the need to monitor seas and oceans is becoming fundamental to improve our knowledge of both physical and chemical phenomena that evolve in the marine environment.

The above context motivates this Special Issue, which aims to investigate matters relating to:

1) technologies for sea observation and monitoring (waves, currents, bathymetry, wind);

2) monitoring of water chemical and physical parameters;

3) assimilation of marine coastal and deep environment data into numerical models;

4) technology and techniques for oil spill detection and analysis;

5) technologies and techniques for ships and objects detection.

Authors are required to check and follow online Instructions to Authors, see https://www.mdpi.com/journal/remotesensing/instructions

Dr. Francesco Serafino
Dr. Claudio Lugni
Prof. Maurizio Brocchini
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access bimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Radar data analysis
  • ocean wave
  • ocean currents
  • bathymetry reconstruction
  • direct-inverse modeling

Published Papers (15 papers)

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Research

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Open AccessArticle Influence of Sea State on Sea Surface Height Oscillation from Doppler Altimeter Measurements in the North Sea
Remote Sens. 2018, 10(7), 1100; https://doi.org/10.3390/rs10071100
Received: 31 May 2018 / Revised: 26 June 2018 / Accepted: 6 July 2018 / Published: 10 July 2018
Cited by 1 | PDF Full-text (5257 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports on an investigation on the influence of waves on the sea surface height error, σh, as measured by Delay Doppler satellite altimetry (DDA). CryoSat-2 altimeter sea surface height (SSH) data in the North Sea, processed in both DDA
[...] Read more.
This paper reports on an investigation on the influence of waves on the sea surface height error, σh, as measured by Delay Doppler satellite altimetry (DDA). CryoSat-2 altimeter sea surface height (SSH) data in the North Sea, processed in both DDA and pseudo low resolution mode (PLRM), are correlated with European Centre for Medium-Range Weather Forecasts (ECMWF) co-located sea state data. We find a small, but consistent correlation between the 1 Hz standard deviation, σh, of the 20 Hz altimeter SSH and the ECMWF total significant wave height, SWHt. The same analysis carried out between σh and the swell component of the wave spectrum shows a smaller correlation. In contrast, the correlation between the PLRM σh and any component of the SWH spectrum has not been found to be significant. To provide an explanation of these results, the aliasing effect caused by the interaction between the sea wavelength and the altimeter resolution has been considered; a simple model has, therefore, been produced to simulate the dependence of the aliasing-derived, σA, on the sea wavelength. The alias/wavelength curve obtained helps to explain why—at least for the relatively low wavelength sea data considered—the wave direction and its wavelength have little or no influence on σh. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Estimation of Surface Duct Using Ground-Based GPS Phase Delay and Propagation Loss
Remote Sens. 2018, 10(5), 724; https://doi.org/10.3390/rs10050724
Received: 24 March 2018 / Revised: 28 April 2018 / Accepted: 7 May 2018 / Published: 8 May 2018
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Abstract
The propagation of Global Positioning System (GPS) signals at low-elevation angles is significantly affected by a surface duct. In this paper, we present an improved algorithm known as NSSAGA, in which simulated annealing (SA) is combined with the non-dominated sorting genetic algorithm II
[...] Read more.
The propagation of Global Positioning System (GPS) signals at low-elevation angles is significantly affected by a surface duct. In this paper, we present an improved algorithm known as NSSAGA, in which simulated annealing (SA) is combined with the non-dominated sorting genetic algorithm II (NSGA-II). Matched-field processing was used to remotely sense the refractivity structure by using the data of ground-based GPS phase delay and propagation loss from multiple antenna heights. The performance was checked by simulation data with and without noise. In comparison with NSGA-II, the new hybrid algorithm retrieved the refractivity structure more efficiently under various noise conditions. We then modified the objective function and found that matched-field processing is more effective than the conventional least-squares method for inferring the refractivity parameters. Comparing the inversion results and in situ sounding data suggests that the improved method presented herein can capture refractivity characteristics in realistic environments. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Circulation during Storms and Dynamics of Suspended Matter in a Sheltered Coastal Area
Remote Sens. 2018, 10(4), 602; https://doi.org/10.3390/rs10040602
Received: 19 March 2018 / Revised: 9 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
The Gulf of Gaeta, in the western margin of central Italy, is characterized by a coastal morphology that creates a natural sheltered area in which fine sediment settles. The new port regulatory plan provides for dock expansions and dredging works that could alter
[...] Read more.
The Gulf of Gaeta, in the western margin of central Italy, is characterized by a coastal morphology that creates a natural sheltered area in which fine sediment settles. The new port regulatory plan provides for dock expansions and dredging works that could alter the suspended particulate matter (SPM) concentration. The present study investigates the dynamics of the Gulf of Gaeta with a focus on the dynamic processes that affect the fine particle concentration. The study was conducted through a multidisciplinary approach that involves remote sensing acquisitions (satellite imagery and X-band radar), measurements in situ (water sampling, wave buoy, weather station, turbidity station, CTD profiles), and numerical modelling (SWAN and Delft3D FLOW). The X-band radar system supports the analysis of the dynamic processes of the SPM concentration providing a large dataset useful for the hydrodynamic model’s validation. The analysis reveals a strong influence of nearby rivers in modulating the SPM at the regional scale. Short-term high and low fluctuations in SPM concentration within the gulf are triggered by the local effect of the main physical forces. In particular, the direction of events and bottom sediment resuspension play a key role in modulating the SPM concentration while micro-tidal regime does not appear to influence turbidity in the study area. This approach represents an important tool in improving the long-term coastal management strategy from the perspective of sustainable human activities in marine coastal ecosystems. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Wind Direction Extraction from SAR in Coastal Areas
Remote Sens. 2018, 10(2), 261; https://doi.org/10.3390/rs10020261
Received: 31 October 2017 / Revised: 1 February 2018 / Accepted: 5 February 2018 / Published: 8 February 2018
Cited by 2 | PDF Full-text (3767 KB) | HTML Full-text | XML Full-text
Abstract
This paper aims to illustrate and test a method, based on the Two-Dimensional Continuous Wavelet Transform (2D-CWT), developed to extract the wind directions from the Synthetic Aperture Radar (SAR) images. The knowledge of the wind direction is essential to retrieve the wind speed
[...] Read more.
This paper aims to illustrate and test a method, based on the Two-Dimensional Continuous Wavelet Transform (2D-CWT), developed to extract the wind directions from the Synthetic Aperture Radar (SAR) images. The knowledge of the wind direction is essential to retrieve the wind speed by using the radar-backscatter versus wind speed algorithms. The method has been applied to 61 SAR images from different satellites (Envisat, COSMO-SkyMed, Radarsat-2 and Sentinel-1A,B), and the results have been compared with the analysis wind fields from the European Centre for Medium-range Weather Forecasts (ECMWF) model, with in situ reports and with scatterometer data when available. The 2D-CWT method provides satisfactory results, both in areas a few kilometres from the coast and offshore. It is reliable as it produces good direction estimates, no matter what the characteristics of the SAR are. Statistics reports a success in the SAR wind direction estimates in 95% of cases (in 83% of cases the SAR-ECMWF wind direction difference is < ± 20 , in 92 % < ± 30 ) with a mean directional bias B θ < 7 . The SAR derived wind directions cannot be said to be validated, as the data available at present cannot be really representative of the wind field in the coastal area. However, the figures given by SAR winds are highly valuable even not properly validated, providing an independent and unique view of the spatial variability of the wind over the sea, which is possible by using the 2D-CWT method to derive the wind directions. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Reconstructing Seabed Topography from Side-Scan Sonar Images with Self-Constraint
Remote Sens. 2018, 10(2), 201; https://doi.org/10.3390/rs10020201
Received: 22 November 2017 / Revised: 22 January 2018 / Accepted: 26 January 2018 / Published: 29 January 2018
Cited by 1 | PDF Full-text (8640 KB) | HTML Full-text | XML Full-text
Abstract
To obtain the high-resolution seabed topography and overcome the limitations of existing topography reconstruction methods in requiring external bathymetric data and ignoring the effects of sediment variations and Side-Scan Sonar (SSS) image quality, this study proposes a method of reconstructing seabed topography from
[...] Read more.
To obtain the high-resolution seabed topography and overcome the limitations of existing topography reconstruction methods in requiring external bathymetric data and ignoring the effects of sediment variations and Side-Scan Sonar (SSS) image quality, this study proposes a method of reconstructing seabed topography from SSS images with a self-constraint condition. A reconstruction model is deduced by Lambert’s law and the seabed scattering model. A bottom tracking method is put forward to get the along-track SSS towfish heights and the initial seabed topography in the SSS measuring area is established by combining the along-track towfish heights, towfish depths and tidal levels obtained from Global Navigation Satellite System (GNSS). The complete process of reconstructing seabed topography is given by taking the initial topography as self-constraint and the high-resolution seabed topography is finally obtained. Experiments verified the proposed method by the data measured in Zhujiang River, China. The standard deviation of less than 15 cm is achieved and the resolution of the reconstructed topography is about 60 times higher than that of the Digital Elevation Model (DEM) established by bathymetric data. The effects of noise, suspended bodies, refraction of wave in water column, sediment variation, the determination of iteration termination condition as well as the performance of the proposed method under these effects are discussed. Finally, the conclusions are drawn out according to the experiments and discussions. The proposed method provides a simple and efficient way to obtain high-resolution seabed topography from SSS images and is a supplement but not substitution for the existing bathymetric methods. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Assessing the Performance of a Low-Cost Method for Video-Monitoring the Water Surface and Bed Level in the Swash Zone of Natural Beaches
Remote Sens. 2018, 10(1), 49; https://doi.org/10.3390/rs10010049
Received: 26 October 2017 / Revised: 8 December 2017 / Accepted: 23 December 2017 / Published: 2 January 2018
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Abstract
A method to continuously measure bed and water levels along a cross-shore transect of vertical poles is evaluated. This remote sensing based method uses video imagery of swash flows propagating past an array of vertical poles buried on the beach face. Using datasets
[...] Read more.
A method to continuously measure bed and water levels along a cross-shore transect of vertical poles is evaluated. This remote sensing based method uses video imagery of swash flows propagating past an array of vertical poles buried on the beach face. Using datasets collected at two beaches in Chile, the method is compared against measurements obtained with conventional co-localized instruments: LiDAR and ultrasonic distance meters. The present video swash pole technique shows good skill in retrieving swash zone bed level and water levels, while providing the possibility to measure morphological variations at time scales varying from wave groups (tens of seconds) to hours. Discrepancies between video and ultrasonic distance meters are found when short time scales are used, for both depositional and erosion events, but longer duration trends are captured well. Water surface elevations at the wave-by-wave scale proved to be accurate for the backwash phase (root-mean-sqaure-error, RMSE down to 0.028 m, R 2 up to 0.89), when compared against LiDAR. However, discrepancies have been found during the uprush phase (RMSE up to 0.062 m, R 2 down to 0.71), when the influence of the pole on the swash flow generates an overestimation of the water surface. Overall, owing to its simplicity of deployment, low cost and reasonable accuracy, the technique is considered suitable for swash studies. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Quantification of Two-Dimensional Wave Breaking Dissipation in the Surf Zone from Remote Sensing Data
Remote Sens. 2018, 10(1), 38; https://doi.org/10.3390/rs10010038
Received: 30 October 2017 / Revised: 20 December 2017 / Accepted: 21 December 2017 / Published: 26 December 2017
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Abstract
A method for obtaining two dimensional fields of wave breaking energy dissipation in the surfzone is presented. The method relies on acquiring geometrical parameters of the wave roller from remote sensing data. These parameters are then coupled with a dissipation model to obtain
[...] Read more.
A method for obtaining two dimensional fields of wave breaking energy dissipation in the surfzone is presented. The method relies on acquiring geometrical parameters of the wave roller from remote sensing data. These parameters are then coupled with a dissipation model to obtain time averaged two dimensional maps, but also the wave breaking energy dissipation on a wave-by-wave basis. Comparison of dissipation maps as obtained from the present technique and a results from a numerical model, show very good correlation in both structure and magnitude. The location of a rip current can also be observed from the field data. Though in the present work a combination of optical and microwave data is used, the underlying method is independent of the remote sensor platform. Therefore, it offers the possibility to acquire high quality and synoptic estimates that could contribute to the understanding of the surfzone hydrodynamics. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Gaussian Half-Wavelength Progressive Decomposition Method for Waveform Processing of Airborne Laser Bathymetry
Remote Sens. 2018, 10(1), 35; https://doi.org/10.3390/rs10010035
Received: 31 October 2017 / Revised: 19 December 2017 / Accepted: 22 December 2017 / Published: 26 December 2017
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Abstract
In an airborne laser bathymetry system, the full-waveform echo signal is usually recorded by discrete sampling. The accuracy of signal recognition and the amount of effective information that can be extracted by conventional methods are limited. To improve the validity and reliability of
[...] Read more.
In an airborne laser bathymetry system, the full-waveform echo signal is usually recorded by discrete sampling. The accuracy of signal recognition and the amount of effective information that can be extracted by conventional methods are limited. To improve the validity and reliability of airborne laser bathymetry data and to extract more information to better understand the water reflection characteristics, we select the effective portion of the original waveform for further research, suppress random noise, and decompose the selected portion progressively using the half-wavelength Gaussian function with the time sequence of the received echo signals. After parameter optimization, a reasonable and effective reflection component selection mechanism is established to obtain accurate parameters for the reflected components. The processing strategy proposed in this paper reduces the problems of unreasonable decomposition and the reflected pulse peak-position shift caused by echo waveform superposition and offers good precision for waveform decomposition and peak detection. In another experiment, the regional processing result shows an obvious improvement in the shallow water area, and the bottom point cloud is as accurate as the intelligent waveform digitizer (IWD), a subsystem of airborne laser terrain mapping (ALTM). These findings confirm that the proposed method has high potential for application. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Automated Sensing of Wave Inundation across a Rocky Shore Platform Using a Low-Cost Camera System
Remote Sens. 2018, 10(1), 11; https://doi.org/10.3390/rs10010011
Received: 7 November 2017 / Revised: 9 December 2017 / Accepted: 12 December 2017 / Published: 23 December 2017
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Abstract
Rocky coastlines are frequently used for recreation, however, they are often highly exposed and hazardous environments resulting in high risk to visitors. Traditional approaches to managing human safety in coastal settings (such as the surf lifesaving clubs that have proven effective on beaches)
[...] Read more.
Rocky coastlines are frequently used for recreation, however, they are often highly exposed and hazardous environments resulting in high risk to visitors. Traditional approaches to managing human safety in coastal settings (such as the surf lifesaving clubs that have proven effective on beaches) are not necessarily transferable to rock platforms due to their often remote and fragmented distribution and the different recreational uses. As such, a different approach is required. To address this, we present a low-cost camera system to assess the wave hazard on a high-visitation rocky shore platform: the Figure Eight Pools Rock Platform, New South Wales, Australia. The camera system is shown to be highly effective and allows identification of both the distance and frequency of wave inundation on the platform using a novel pixel analysis technique. Nearshore wave height is shown to be the primary factor driving inundation frequencies along the cross-platform transect investigated with some influence from wave period. The remotely sensed camera data are used to develop a preliminary overwash hazard rating system, and analysis of the first month of data collected suggests that the platform is highly hazardous to visitors. Future work will expand this hazard rating system, developing a predictive tool that estimates the overwash hazard level based on forecast wave and tide conditions to improve visitor safety at the site. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle S-Band Doppler Wave Radar System
Remote Sens. 2017, 9(12), 1302; https://doi.org/10.3390/rs9121302
Received: 27 October 2017 / Revised: 8 December 2017 / Accepted: 11 December 2017 / Published: 12 December 2017
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Abstract
In this paper, a novel shore-based S-band microwave Doppler coherent wave radar (Microwave Ocean Remote SEnsor (MORSE)) is designed to improve wave measurements. Marine radars, which operate in the X band, have been widely used for ocean monitoring because of their low cost,
[...] Read more.
In this paper, a novel shore-based S-band microwave Doppler coherent wave radar (Microwave Ocean Remote SEnsor (MORSE)) is designed to improve wave measurements. Marine radars, which operate in the X band, have been widely used for ocean monitoring because of their low cost, small size and flexibility. However, because of the non-coherent measurements and strong absorption of X-band radio waves by rain, these radar systems suffer considerable performance loss in moist weather. Furthermore, frequent calibrations to modify the modulation transfer function are required. To overcome these shortcomings, MORSE, which operates in the S band, was developed by Wuhan University. Because of the coherent measurements of this sensor, it is able to measure the radial velocity of water particles via the Doppler effect. Then the relation between the velocity spectrum and wave height spectrum can be used to obtain the wave height spectra. Finally, wave parameters are estimated from the wave height spectra by the spectrum moment method. Comparisons between MORSE and Waverider MKIII are conducted in this study, and the results, including the non-directional wave height spectra, significant wave height and average wave period, are calculated and displayed. The correlation coefficient of the significant wave height is larger than 0.9, whereas that of the average wave period is approximately 0.4, demonstrating the effectiveness of MORSE for the continuous monitoring of ocean areas with high accuracy. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Wave Height Estimation from First-Order Backscatter of a Dual-Frequency High Frequency Radar
Remote Sens. 2017, 9(11), 1186; https://doi.org/10.3390/rs9111186
Received: 28 September 2017 / Revised: 16 November 2017 / Accepted: 17 November 2017 / Published: 18 November 2017
PDF Full-text (3258 KB) | HTML Full-text | XML Full-text
Abstract
Second-order scattering based wave height measurement with high-frequency (HF) radar has always been subjected to problems such as distance limitation and external interference especially under low or moderate sea state. The performance is further exacerbated for a compact system with small antennas. First-order
[...] Read more.
Second-order scattering based wave height measurement with high-frequency (HF) radar has always been subjected to problems such as distance limitation and external interference especially under low or moderate sea state. The performance is further exacerbated for a compact system with small antennas. First-order Bragg scattering has been investigated to relate wave height to the stronger Bragg backscatter, but calibrating the echo power along distance and direction is challenging. In this paper, a new method is presented to deal with the calibration and improve the Bragg scattering based wave height estimation from dual-frequency radar data. The relative difference of propagation attenuation and directional spreading between two operating frequencies has been found to be identifiable along range and almost independent of direction, and it is employed to effectively reduce the fitting requirements of in situ wave buoys. A 20-day experiment was performed over the Taiwan Strait of China to validate this method. Comparison of wave height measured by radar and buoys at distance of 15 km and 70 km shows that the root-mean-square errors are 0.34 m and 0.56 m, respectively, with correlation coefficient of 0.82 and 0.84. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Ship Detection in Optical Remote Sensing Images Based on Wavelet Transform and Multi-Level False Alarm Identification
Remote Sens. 2017, 9(10), 985; https://doi.org/10.3390/rs9100985
Received: 10 July 2017 / Revised: 18 September 2017 / Accepted: 20 September 2017 / Published: 22 September 2017
Cited by 4 | PDF Full-text (10440 KB) | HTML Full-text | XML Full-text
Abstract
Ship detection by Unmanned Airborne Vehicles (UAVs) and satellites plays an important role in a spectrum of related military and civil applications. To improve the detection efficiency, accuracy, and speed, a novel ship detection method from coarse to fine is presented. Ship targets
[...] Read more.
Ship detection by Unmanned Airborne Vehicles (UAVs) and satellites plays an important role in a spectrum of related military and civil applications. To improve the detection efficiency, accuracy, and speed, a novel ship detection method from coarse to fine is presented. Ship targets are viewed as uncommon regions in the sea background caused by the differences in colors, textures, shapes, or other factors. Inspired by this fact, a global saliency model is constructed based on high-frequency coefficients of the multi-scale and multi-direction wavelet decomposition, which can characterize different feature information from edge to texture of the input image. To further reduce the false alarms, a new and effective multi-level discrimination method is designed based on the improved entropy and pixel distribution, which is robust against the interferences introduced by islands, coastlines, clouds, and shadows. The experimental results on optical remote sensing images validate that the presented saliency model outperforms the comparative models in terms of the area under the receiver operating characteristic curves core and the accuracy in the images with different sizes. After the target identification, the locations and the number of the ships in various sizes and colors can be detected accurately and fast with high robustness. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessArticle Sea Wind Measurement by Doppler Navigation System with X-Configured Beams in Rectilinear Flight
Remote Sens. 2017, 9(9), 887; https://doi.org/10.3390/rs9090887
Received: 7 June 2017 / Revised: 8 August 2017 / Accepted: 9 August 2017 / Published: 26 August 2017
Cited by 1 | PDF Full-text (7940 KB) | HTML Full-text | XML Full-text
Abstract
We suggest a conceptual approach to the measurement of the near-surface wind vector over water using a Doppler navigation system, in addition to its standard navigation capabilities. We consider a Doppler navigation system with a track-stabilized antenna and x-configuration of its beams.
[...] Read more.
We suggest a conceptual approach to the measurement of the near-surface wind vector over water using a Doppler navigation system, in addition to its standard navigation capabilities. We consider a Doppler navigation system with a track-stabilized antenna and x-configuration of its beams. For the measurement of the sea-surface wind, the system operates in the multi-beam scatterometer mode in rectilinear flight. The proposed conceptual design has been validated, and its accuracy for the wind vector measurement has been estimated using Monte Carlo computational simulations. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Other

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Open AccessTechnical Note Knowledge-Based Generalized Side-Lobe Canceller for Ionospheric Clutter Suppression in HFSWR
Remote Sens. 2018, 10(1), 104; https://doi.org/10.3390/rs10010104
Received: 30 October 2017 / Revised: 18 December 2017 / Accepted: 12 January 2018 / Published: 13 January 2018
Cited by 1 | PDF Full-text (5497 KB) | HTML Full-text | XML Full-text
Abstract
High frequency surface wave radar (HFSWR) has been successfully developed for early warning and remote sensing. However, the ionospheric clutter is a difficult challenge that can make HFSWR system inefficient. The Generalized Side-lobe Canceller (GSC) has been proved to be an effective algorithm
[...] Read more.
High frequency surface wave radar (HFSWR) has been successfully developed for early warning and remote sensing. However, the ionospheric clutter is a difficult challenge that can make HFSWR system inefficient. The Generalized Side-lobe Canceller (GSC) has been proved to be an effective algorithm for clutter suppression in theory, but it suffers from the performance degradation for some non-ideal conditions in practice. The most intolerable shortcoming is the signal to noise ratio (SNR) loss caused by the residual signal in the secondary data. In this paper, a knowledge-based GSC (KB-GSC) method has been proposed via an adaptive single notch filter design to reject the residual signal for reducing the SNR loss. The feasibility and availability has been demonstrated by measured data. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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Open AccessTechnical Note Performance Analysis of Ship Wake Detection on Sentinel-1 SAR Images
Remote Sens. 2017, 9(11), 1107; https://doi.org/10.3390/rs9111107
Received: 27 September 2017 / Revised: 26 October 2017 / Accepted: 27 October 2017 / Published: 30 October 2017
PDF Full-text (3624 KB) | HTML Full-text | XML Full-text
Abstract
A novel technique for ship wake detection has been recently proposed and applied on X-band Synthetic Aperture Radar images provided by COSMO/SkyMed and TerraSAR-X. The approach shows that the vast majority of wake features are correctly detected and validated in critical situations. In
[...] Read more.
A novel technique for ship wake detection has been recently proposed and applied on X-band Synthetic Aperture Radar images provided by COSMO/SkyMed and TerraSAR-X. The approach shows that the vast majority of wake features are correctly detected and validated in critical situations. In this paper, the algorithm was applied to 28 wakes imaged by Sentinel-1 mission with different polarizations and incidence angles with the aim of testing the method’s robustness with reference to radar frequency and resolution. The detection process is properly modified. The results show that the features were correctly classified in 78.5% of cases, whereas false confirmations occur mainly on Kelvin cusps. Finally, the results were compared with the algorithm performance on X-band images, showing that no significant difference arises. In fact, the total false confirmations rate was 15.8% on X-band images and 18.5% on C-band images. Moreover, since the main criticality concerns again the false confirmation of Kelvin cusps, the same empirical criterion suggested for the X-band SAR images yielded a negligible 1.5% of false detection rate. Full article
(This article belongs to the Special Issue Instruments and Methods for Ocean Observation and Monitoring)
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