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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Remote Sensors".

Deadline for manuscript submissions: closed (30 November 2022) | Viewed by 31064

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Special Issue Editors

Prof. Filippo Giannetti

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Guest Editor

Dipartimento di Ingegneria dell'Informazione (DII), University of Pisa, Italy
Interests: wireless and mobile communications; satellite communications systems; radiopropagation; photonics; environmental monitoring; digital signal processing

Prof. Dr. Luca Giovanni Lanza

E-Mail Website
Guest Editor

Department of Civil, Chemical and Environmental Engineering (DICCA), University of Genova, 1 Montallegro, 16145 Genova GE, Italy
Interests: hydrology; precipitation; measurement; green roofs; nature-based solutions; sustainable urban drainage
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Rain detection and monitoring is essential for many human activities, such as agriculture, water management, transportation, tourism, and leisure. Furthermore, the increasing occurrence of extreme precipitation events caused by climate changes calls for urgent improvements in operational measurement techniques of the rainfall amount and intensity. Therefore, the need for the development of new sensors, together with the definition of the relevant calibration and standardization procedures, becomes ever more pressing.

In this context, this Special Issue aims to collect a number of papers about rain sensor technologies and applications, with the goal of providing the readership with an understanding of operating principles, state-of-the-art, applications, and future trends of such devices. This Special Issue thus welcomes contributions by researchers from both academia and industry on all aspects of rain sensor technologies and applications, spanning over different measuring principles, measurement scales, and the measured characteristics of the rainfall process (intensity, drop size distribution, fall velocity, etc.). Papers are also invited on the various aspects of sensor calibration, uncertainty assessment, standardization, and validation.

Contributions can be in the form of tutorials, surveys, and feature papers presenting the state-of-the-art of the technology, applications, case studies, prototypes, results of measurement campaigns, and innovative solutions.

In cooperation with project SCORE (Smart Control of the Climate Resilience in European Coastal Cities), funded by European Union’s Horizon 2020 programme under grant agreement No. 101003534.

Prof. Filippo Giannetti
Prof. Dr. Luca Giovanni Lanza
Guest Editors

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Keywords

rain sensors
rain gauges
tipping buckets
disdrometers
weather radars
microwave propagation
rain fading
satellites
meteorology
climatology
hydrology
civil protection
agriculture
water management
automotive
environmental monitoring
sensor networks

Published Papers (17 papers)

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Research

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Open AccessArticle

Prediction of Actual from Climatic Precipitation with Data Collected from Northern Poland: A Statistical Approach

Cécil J. W. Meulenberg

Peter Kumer

Włodzimierz Golus

and

Maciej Markowski

Sensors 2023, 23(3), 1159; https://doi.org/10.3390/s23031159 - 19 Jan 2023

Viewed by 577

Abstract

Water is a basic element of the natural environment and the most important component in human water management. Rainfall is the main source of water. Therefore, determining the amount of precipitation reaching the ground using sensors is crucial information. Precise precipitation data are necessary for better modeling quality, as the observation data from weather stations are used as basics for weather model assessment. The authors compared precipitation from the Hellmann rain gauge (climatic precipitation, 1.0 m above the ground surface) measured throughout the year and the GGI 3000 rain gauge (actual precipitation on the ground level) measured from April to October. Measurement sequences from the years 2011–2020 were considered. The data for analysis were obtained from a weather station located in northern Poland. The authors analyzed the relationships between data from the two sensors. A comparative study showed that the measurements of actual precipitation are higher and there are strong relationships between actual and climatic rainfall (r = 0.99). Using the introduced coefficient it is possible to determine the full–year actual precipitation with high probability, taking into account the precipitation with a correction from the winter half-year and the actual precipitation from the summer half-year, which is of great importance in the calculation of the water balance. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Rainfall Map from Attenuation Data Fusion of Satellite Broadcast and Commercial Microwave Links

Fabio Saggese

Vincenzo Lottici

and

Filippo Giannetti

Sensors 2022, 22(18), 7019; https://doi.org/10.3390/s22187019 - 16 Sep 2022

Viewed by 752

Abstract

The demand for accurate rainfall rate maps is growing ever more. This paper proposes a novel algorithm to estimate the rainfall rate map from the attenuation measurements coming from both broadcast satellite links (BSLs) and commercial microwave links (CMLs). The approach we pursue is based on an iterative procedure which extends the well-known GMZ algorithm to fuse the attenuation data coming from different links in a three-dimensional scenario, while also accounting for the virga phenomenon as a rain vertical attenuation model. We experimentally prove the convergence of the procedures, showing how the estimation error decreases for every iteration. The numerical results show that adding the BSL links to a pre-existent CML network boosts the accuracy performance of the estimated rainfall map, improving up to 50% the correlation metrics. Moreover, our algorithm is shown to be robust to errors concerning the virga parametrization, proving the possibility of obtaining good estimation performance without the need for precise and real-time estimation of the virga parameters. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Development and Calibration of a Low-Cost, Piezoelectric Rainfall Sensor through Machine Learning

and

Sensors 2022, 22(17), 6638; https://doi.org/10.3390/s22176638 - 02 Sep 2022

Viewed by 1154

Abstract

In situ measurements of precipitation are typically obtained by tipping bucket or weighing rain gauges or by disdrometers using different measurement principles. One of the most critical aspects of their operational use is the calibration, which requires the characterization of instrument responses both in laboratory and in real conditions. Another important issue with in situ measurements is the coverage. Dense networks are desirable, but the installation and maintenance costs can be unaffordable with most of the commercial conventional devices. This work presents the development of a prototype of an impact rain gauge based on a very low-cost piezoelectric sensor. The sensor was developed by assembling off-the-shelf and reused components following an easy prototyping approach; the calibration of the relationship between the different properties of the voltage signal, as sampled by the rain drop impact, and rainfall intensity was established using machine-learning methods. The comparison with 1-minute rainfall obtained by a co-located commercial disdrometer highlights the fairly good performance of the low-cost sensor in monitoring and characterizing rainfall events. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Calibration Uncertainty of Non-Catching Precipitation Gauges

Peter Friis Østergaard

Marina Parrondo

and

Carmen Garcia Izquierdo

Sensors 2022, 22(17), 6413; https://doi.org/10.3390/s22176413 - 25 Aug 2022

Cited by 1 | Viewed by 768

Abstract

Precipitation is among the most important meteorological variables for, e.g., meteorological, hydrological, water management and climate studies. In recent years, non-catching precipitation gauges are increasingly adopted in meteorological networks. Despite such growing diffusion, calibration procedures and associated uncertainty budget are not yet standardized or prescribed in best practice documents and standards. This paper reports a metrological study aimed at proposing calibration procedures and completing the uncertainty budgets, to make non-catching precipitation gauge measurements traceable to primary standards. The study is based on the preliminary characterization of different rain drop generators, specifically developed for the investigation. Characterization of different models of non-catching rain gauges is also included. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Cross-Evaluation of Reflectivity from NEXRAD and Global Precipitation Mission during Extreme Weather Events

and

Sensors 2022, 22(15), 5773; https://doi.org/10.3390/s22155773 - 02 Aug 2022

Viewed by 949

Abstract

During extreme events such as tropical cyclones, the precision of sensors used to sample the meteorological data is vital to feed weather and climate models for storm path forecasting, quantitative precipitation estimation, and other atmospheric parameters. For this reason, periodic data comparison between several sensors used to monitor these phenomena such as ground-based and satellite instruments, must maintain a high degree of correlation in order to issue alerts with an accuracy that allows for timely decision making. This study presents a cross-evaluation of the radar reflectivity from the dual-frequency precipitation radar (DPR) onboard the Global Precipitation Measurement Mission (GPM) and the U.S. National Weather Service (NWS) Next-Generation Radar (NEXRAD) ground-based instrument located in the Caribbean island of Puerto Rico, USA, to determine the correlation degree between these two sensors’ measurements during extreme weather events and normal precipitation events during 2015–2019. GPM at Ku-band and Ka-band and NEXRAD at S-band overlapping scanning regions data of normal precipitation events during 2015–2019, and the spiral rain bands of four extreme weather events, Irma (Category 5 Hurricane), Beryl (Tropical Storm), Dorian (Category 1 hurricane), and Karen (Tropical Storm), were processed using the GPM Ground Validation System (GVS). In both cases, data were classified and analyzed statistically, paying particular attention to variables such as elevation angle mode and precipitation type (stratiform and convective). Given that ground-based radar (GR) has better spatial and temporal resolution, the NEXRAD was used as ground-truth. The results revealed that the correlation coefficient between the data of both instruments during the analyzed extreme weather events was moderate to low; for normal precipitation events, the correlation is lower than that of studies that compared GPM and NEXRAD reflectivity located in other regions of the USA. Only Tropical Storm Karen obtained similar results to other comparative studies in terms of the correlation coefficient. Furthermore, the GR elevation angle and precipitation type have a substantial impact on how well the rain reflectivity correlates between the two sensors. It was found that the Ku-band channel possesses the least bias and variability when compared to the NEXRAD instrument’s reflectivity and should therefore be considered more reliable for future tropical storm tracking and tropical region precipitation estimates in regions with no NEXRAD coverage. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Comparison of CML Rainfall Data against Rain Gauges and Disdrometers in a Mountainous Environment

and

Sensors 2022, 22(9), 3218; https://doi.org/10.3390/s22093218 - 22 Apr 2022

Cited by 1 | Viewed by 975

Abstract

Despite the several sources of inaccuracy, commercial microwave links (CML) have been recently exploited to estimate the average rainfall intensity along the radio path from signal attenuation. Validating these measurements against “ground truth” from conventional rainfall sensors, as rain gauges, is a challenging issue due to the different spatial sampling involved. Here, we assess the performance of a network of CML as opportunistic rainfall sensors in a challenging mountainous environment located in Northern Italy. The benchmark dataset was provided by an operational network of rain gauges and by three disdrometers. Moreover, disdrometer data were used to establish an accurate relationship between path attenuation and rainfall intensity. A new method was developed for assessing CML: time series of rainfall occurrence and rainfall depth, representative of CML radio path, were derived from the nearby rain gauges and disdrometers and compared with the same quantities gathered from the CML. It turns out that, over the very short integration times considered (10 min), CML perform well in detecting rainfall, whereas quantitative rainfall estimates may have large discrepancies. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Low-Cost Ka-Band Satellite Receiver Data Preprocessing for Tropospheric Propagation Studies

Vicente Pastoriza-Santos

Fernando Machado

Dalia Nandi

and

Fernando Pérez-Fontán

Sensors 2022, 22(3), 1043; https://doi.org/10.3390/s22031043 - 28 Jan 2022

Cited by 1 | Viewed by 1607

Abstract

Satellite tropospheric propagation studies strongly rely on beacon receiver measurements. We were interested in performing a measurement campaign to characterize rain attenuation statistics. In this article, we outline some of the characteristics and drawbacks one faces when trying to perform a radio wave satellite beacon propagation experiment at the Ka-band with low-cost measurement equipment. We used an affordable beacon receiver consisting of a commercial low-noise block down-converter, an outdoor dual-reflector antenna, and a software-defined radio unit. To measure rain attenuation events, we needed to work out where the reference signal level was at all times. However, as we did not have a radiometer to remove the impact of gases and clouds, since it is a very expensive device, we used a procedure that involved the subtraction of a stable and reliable reference level (template) from the raw received beacon level. This template was extracted from observations during non-rainy periods. The procedure implemented for extracting the template was based on the same data processing methodology used by other authors in this field. Here, we describe through specific examples the main characteristics of the templates extracted on non-rainy days, as well as the impact of some meteorological parameters and unavoidable, but small antenna pointing errors. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

A Propagation Study of LoRa P2P Links for IoT Applications: The Case of Near-Surface Measurements over Semitropical Rivers

Amado Gutiérrez-Gómez

Jesús López-De la Cruz

Oliver Mendoza-Cano

Miguel Lopez-Guerrero

and

Yu Geng

Sensors 2021, 21(20), 6872; https://doi.org/10.3390/s21206872 - 16 Oct 2021

Cited by 4 | Viewed by 2782

Abstract

Internet of Things (IoT) radio networks are becoming popular in several scenarios for short-range applications (e.g., wearables and home security) and medium-range applications (e.g., shipping container tracking and autonomous farming). They have also been proposed for water monitoring in flood warning systems. IoT communications may use long range (LoRa) radios working in the 915 MHz industrial, scientific and medical (ISM) band. In this research, we study the propagation characteristics of LoRa chirp radio signals close to and over water in a tropical meadow region. We use as a case study the Colima River in Mexico. We develop a novel point-to-point IoT measurement sounding system that does not require decoding of LoRa propriety bursts and provides accurate power versus distance profiles along the riparian zone of a steeply dropping mountain river. We used this system to obtain the measurements reported in this work, which are also analyzed and modeled. The results show that the LoRa signal propagation over water exhibits a log-normal distribution. As a result of the chirp signal processing, two new experimental path loss models are presented. The path loss results show a considerable degradation of the received signal power over water within vegetation and less signal degradation at antenna heights closer to the water surface. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Rainfall Intensity and Quantity Estimation Method Based on Gamma-Dose Rate Monitoring

and

Sensors 2021, 21(19), 6411; https://doi.org/10.3390/s21196411 - 25 Sep 2021

Cited by 1 | Viewed by 1236

Abstract

The features of the atmospheric

γ

-background reaction to liquid atmospheric precipitation in the form of bursts is investigated, and various forms of them are analyzed. A method is described for interpreting forms of the measured

γ

-background response with the determination of [...] Read more.

The features of the atmospheric

γ

-background reaction to liquid atmospheric precipitation in the form of bursts is investigated, and various forms of them are analyzed. A method is described for interpreting forms of the measured

γ

-background response with the determination of the beginning and ending time of precipitation, the distinctive features of changes in the intensity of precipitation and the number of single (separate) events that form one burst. It is revealed that a change in the intensity of precipitation in one event leads to a change in the

γ

-radiation dose rate increase speed (time derivative). A method of estimating the average value of the intensity and amount of precipitation for one event, reconstructing the intensity spectrum from experimental data on the dynamics of the measured dose rate of

γ

-radiation, is developed. The method takes into account the radioactive decay of radon daughter products in the atmosphere and on the soil surface during precipitation, as well as the purification of the atmosphere from radionuclides. Recommendations are given for using the developed method to correct for changes (daily variations) in radon flux density from the ground surface, which lead to variations in radon in the atmosphere. Experimental verification of the method shows good agreement between the values of the intensity of liquid atmospheric precipitation, calculated and measured with the help of shuttle and optical rain precipitation gauges. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessCommunication

Retrieval of Raindrop Size Distribution Using Dual-Polarized Microwave Signals from LEO Satellites: A Feasibility Study through Simulations

Xi Shen

and

Defeng David Huang

Sensors 2021, 21(19), 6389; https://doi.org/10.3390/s21196389 - 24 Sep 2021

Cited by 1 | Viewed by 1196

Abstract

In this paper, a novel approach for raindrop size distribution retrieval using dual-polarized microwave signals from low Earth orbit satellites is proposed. The feasibility of this approach is studied through modelling and simulating the retrieval system which includes multiple ground receivers equipped with signal-to-noise ratio estimators and a low Earth orbit satellite communicating with the receivers using both vertically and horizontally polarized signals. Our analysis suggests that the dual-polarized links offer the opportunity to estimate two independent raindrop size distribution parameters. To achieve that, the vertical and horizontal polarization attenuations need to be measured at low elevation angles where the difference between them is more distinct. Two synthetic rain fields are generated to test the performance of the retrieval. Simulation results suggest that the specific attenuations for both link types can be retrieved through a least-squares algorithm. They also confirm that the specific attenuation ratio of vertically to horizontally polarized signals can be used to retrieve the slope and intercept parameters of raindrop size distribution. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

On the Use of Dynamic Calibration to Correct Drop Counter Rain Gauge Measurements

and

Sensors 2021, 21(18), 6321; https://doi.org/10.3390/s21186321 - 21 Sep 2021

Cited by 1 | Viewed by 1581

Abstract

Dynamic calibration was performed in the laboratory on two catching-type drop counter rain gauges manufactured as high-sensitivity and fast response instruments by Ogawa Seiki Co. Ltd. (Japan) and the Chilbolton Rutherford Appleton Laboratory (UK). Adjustment procedures were developed to meet the recommendations of the World Meteorological Organization (WMO) for rainfall intensity measurements at the one-minute time resolution. A dynamic calibration curve was derived for each instrument to provide the drop volume variation as a function of the measured drop releasing frequency. The trueness of measurements was improved using a post-processing adjustment algorithm and made compatible with the WMO recommended maximum admissible error. The impact of dynamic calibration on the rainfall amount measured in the field at the annual and the event scale was calculated for instruments operating at two experimental sites. The rainfall climatology at the site is found to be crucial in determining the magnitude of the measurement bias, with a predominant overestimation at the low to intermediate rainfall intensity range. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Investigation of the Wind-Induced Airflow Pattern Near the Thies LPM Precipitation Gauge

and

Sensors 2021, 21(14), 4880; https://doi.org/10.3390/s21144880 - 17 Jul 2021

Cited by 3 | Viewed by 1403

Abstract

The airflow velocity pattern generated by a widely used non-catching precipitation gauge (the Thies laser precipitation monitor or LPM) when immersed in a wind field is investigated using computational fluid dynamics (CFD). The simulation numerically solves the unsteady Reynolds-averaged Navier–Stokes (URANS) equations and the setup is validated against dedicated wind tunnel measurements. The adopted k-ω shear stress transport (SST) turbulence model closely reproduces the flow pattern generated by the complex, non-axisymmetric outer geometry of the instrument. The airflow pattern near the measuring area varies with the wind direction, the most intense recirculating flow and turbulence being observed when the wind blows from the back of the instrument. Quantitative parameters are used to discuss the magnitude of the airflow perturbations with respect to the ideal configuration where the instrument is transparent to the wind. The generated airflow pattern is expected to induce some bias in operational measurements, especially in strong wind conditions. The proposed numerical simulation framework provides a basis to develop correction curves for the wind-induced bias of non-catching gauges, as a function of the undisturbed wind speed and direction. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Rain Area Detection in South-Western Kenya by Using Multispectral Satellite Data from Meteosat Second Generation

and

Sensors 2021, 21(10), 3547; https://doi.org/10.3390/s21103547 - 19 May 2021

Cited by 2 | Viewed by 2674

Abstract

This study presents a rain area detection scheme that uses a gradient based adaptive technique for daytime and nighttime rain area detection and correction from reflectance and infrared (IR) brightness temperatures data of the Meteosat Second Generation (MSG) satellite. First, multiple parametric rain detection models developed from MSG’s reflectance and IR data were calibrated and validated with rainfall data from a dense network of rain gauge stations and investigated to determine the best model parameters. The models were based on a conceptual assumption that clouds characterised by the top properties, e.g., high optical thickness and effective radius, have high rain probabilities and intensities. Next, a gradient based adaptive correction technique that relies on rain area-specific parameters was developed to reduce the number and sizes of the detected rain areas. The daytime detection with optical (VIS0.6) and near IR (NIR1.6) reflectance data achieved the best detection skill. For nighttime, detection with thermal IR brightness temperature differences of IR3.9-IR10.8, IR3.9-WV73 and IR108-WV62 showed the best detection skill based on general categorical statistics. Compared to the Global Precipitation Measurement (GPM) Integrated Mult-isatellitE Retrievals for GPM (IMERG) and the gauge station data from the southwest of Kenya, the model showed good agreement in the spatial dynamics of the detected rain area and rain rate. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessArticle

Research on Rainfall Monitoring Based on E-Band Millimeter Wave Link in East China

and

Sensors 2021, 21(5), 1670; https://doi.org/10.3390/s21051670 - 01 Mar 2021

Cited by 5 | Viewed by 2079

Abstract

Accurate rainfall observation data with high temporal and spatial resolution are essential for national disaster prevention and mitigation as well as climate response decisions. This paper introduces a field experiment using an E-band millimeter-wave link to obtain rainfall rate information in Nanjing city, which is situated in the east of China. The link is 3 km long and operates at 71 and 81 GHz. We first distinguish between the wet and the dry periods, and then determine the classification threshold for calculating attenuation baseline in real time. We correct the influence of the wet antenna attenuation and finally calculate the rainfall rate through the power law relationship between the rainfall rate and the rain-induced attenuation. The experimental results show that the correlation between the rainfall rate retrieved from the 71 GHz link and the rainfall rate measured by the raindrop spectrometer is up to 0.9. The correlation at 81 GHz is up to 0.91. The mean relative errors are all below 5%. By comparing with the rainfall rate measured by the laser raindrop spectrometer set up at the experimental site, we verified the reliability and accuracy of monitoring rainfall using the E-band millimeter-wave link. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessCommunication

Real-Time Rainfall Estimation Using Microwave Links: A Case Study in East China during the Plum Rain Season in 2020

Kun Song

Xichuan Liu

and

Taichang Gao

Sensors 2021, 21(3), 858; https://doi.org/10.3390/s21030858 - 28 Jan 2021

Cited by 10 | Viewed by 1511

Abstract

Accurate and real-time rainfall estimation is a pressing need for forecasting the flood disaster and reducing the loss. In this study, we exploit the potential of estimating the rainfall by microwave links in East China. Eight microwave links at 15 GHz and 23 GHz, operated by China Mobile, are used for estimating the rain rate in real-time in Jiangyin, China from June to July 2020. First, we analyze the correlation between the rain-induced attenuation of microwave links and the rain rate measured by rain gauges. The correlation coefficient values are higher than 0.77 with the highest one over 0.9, showing a strong positive correlation. The real-time results indicate that microwave links estimate the rainfall with a higher temporal resolution than the rain gauges. Meanwhile, the rain rate that was estimated by microwave links also correlates well with the actual rain rate, and most of the values of the mean absolute error are less than 1.50 mm/h. Besides, the total rainfall’s relative deviation values are less than 5% with the smallest one reaching 1%. The quantitative results also indicate that microwave links could lead to better forecasting of water levels and, hence, better warnings for flood disasters. Full article

(This article belongs to the Special Issue Rain Sensors)

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Review

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Open AccessReview

A Review on Rainfall Measurement Based on Commercial Microwave Links in Wireless Cellular Networks

and

Sensors 2022, 22(12), 4395; https://doi.org/10.3390/s22124395 - 10 Jun 2022

Cited by 2 | Viewed by 1555

Abstract

As one of the most critical elements in the hydrological cycle, real-time and accurate rainfall measurement is of great significance to flood and drought disaster risk assessment and early warning. Using commercial microwave links (CMLs) to conduct rainfall measure is a promising solution due to the advantages of high spatial resolution, low implementation cost, near-surface measurement, and so on. However, because of the temporal and spatial dynamics of rainfall and the atmospheric influence, it is necessary to go through complicated signal processing steps from signal attenuation analysis of a CML to rainfall map. This article first introduces the basic principle and the revolution of CML-based rainfall measurement. Then, the article illustrates different steps of signal process in CML-based rainfall measurement, reviewing the state of the art solutions in each step. In addition, uncertainties and errors involved in each step of signal process as well as their impacts on the accuracy of rainfall measurement are analyzed. Moreover, the article also discusses how machine learning technologies facilitate CML-based rainfall measurement. Additionally, the applications of CML in monitoring phenomena other than rain and the hydrological simulation are summarized. Finally, the challenges and future directions are discussed. Full article

(This article belongs to the Special Issue Rain Sensors)

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Open AccessReview

Opportunistic Rain Rate Estimation from Measurements of Satellite Downlink Attenuation: A Survey

Filippo Giannetti

and

Ruggero Reggiannini

Sensors 2021, 21(17), 5872; https://doi.org/10.3390/s21175872 - 31 Aug 2021

Cited by 8 | Viewed by 3226

Abstract

Recent years have witnessed a growing interest in techniques and systems for rainfall surveillance on regional scale, with increasingly stringent requirements in terms of the following: (i) accuracy of rainfall rate measurements, (ii) adequate density of sensors over the territory, (iii) space-time continuity and completeness of data and (iv) capability to elaborate rainfall maps in near real time. The devices deployed to monitor the precipitation fields are traditionally networks of rain gauges distributed throughout the territory, along with weather radars and satellite remote sensors operating in the optical or infrared band, none of which, however, are suitable for full compliance to all of the requirements cited above. More recently, a different approach to rain rate estimation techniques has been proposed and investigated, based on the measurement of the attenuation induced by rain on signals of pre-existing radio networks either in terrestrial links, e.g., the backhaul connections in cellular networks, or in satellite-to-earth links and, among the latter, notably those between geostationary broadcast satellites and domestic subscriber terminals in the Ku and Ka bands. Knowledge of the above rain-induced attenuation permits the retrieval of the corresponding rain intensity provided that a number of meteorological and geometric parameters are known and ultimately permits estimating the rain rate locally at the receiver site. In this survey paper, we specifically focus on such a type of “opportunistic” systems for rain field monitoring, which appear very promising in view of the wide diffusion over the territory of low-cost domestic terminals for the reception of satellite signals, prospectively allowing for a considerable geographical capillarity in the distribution of sensors, at least in more densely populated areas. The purpose of the paper is to present a broad albeit synthetic overview of the numerous issues inherent in the above rain monitoring approach, along with a number of solutions and algorithms proposed in the literature in recent years, and ultimately to provide an exhaustive account of the current state of the art. Initially, the main relevant aspects of the satellite link are reviewed, including those related to satellite dynamics, frequency bands, signal formats, propagation channel and radio link geometry, all of which have a role in rainfall rate estimation algorithms. We discuss the impact of all these factors on rain estimation accuracy while also highlighting the substantial differences inherent in this approach in comparison with traditional rain monitoring techniques. We also review the basic formulas relating rain rate intensity to a variation of the received signal level or of the signal-to-noise ratio. Furthermore, we present a comprehensive literature survey of the main research issues for the aforementioned scenario and provide a brief outline of the algorithms proposed for their solution, highlighting their points of strength and weakness. The paper includes an extensive list of bibliographic references from which the material presented herein was taken. Full article

(This article belongs to the Special Issue Rain Sensors)

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