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Real-Time Rain Rate Evaluation via Satellite Downlink Signal Attenuation Measurement

DOI:10.3390/s17081864
Authors:
Filippo Giannetti at Università di Pisa
Filippo Giannetti
Ruggero Reggiannini at Università di Pisa
Ruggero Reggiannini
Marco Moretti at Università di Pisa
Marco Moretti
Elisa Adirosi at Italian National Research Council
Elisa Adirosi
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Abstract and Figures

We present the NEFOCAST project (named by the contraction of "Nefele", which is the Italian spelling for the mythological cloud nymph Nephele, and "forecast"), funded by the Tuscany Region, about the feasibility of a system for the detection and monitoring of precipitation fields over the regional territory based on the use of a widespread network of new-generation Eutelsat "SmartLNB" (smart low-noise block converter) domestic terminals. Though primarily intended for interactive satellite services, these devices can also be used as weather sensors, as they have the capability of measuring the rain-induced attenuation incurred by the downlink signal and relaying it on an auxiliary return channel. We illustrate the NEFOCAST system architecture, consisting of the network of ground sensor terminals, the space segment, and the service center, which has the task of processing the information relayed by the terminals for generating rain field maps. We discuss a few methods that allow the conversion of a rain attenuation measurement into an instantaneous rainfall rate. Specifically, we discuss an exponential model relating the specific rain attenuation to the rainfall rate, whose coefficients were obtained from extensive experimental data. The above model permits the inferring of the rainfall rate from the total signal attenuation provided by the SmartLNB and from the link geometry knowledge. Some preliminary results obtained from a SmartLNB installed in Pisa are presented and compared with the output of a conventional tipping bucket rain gauge. It is shown that the NEFOCAST sensor is able to track the fast-varying rainfall rate accurately with no delay, as opposed to a conventional gauge.
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Real-Time Rain Rate Evaluation via Satellite Downlink Signal Attenuation Measureme
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... Recently, a significant research effort has been devoted also to the estimation of the rainfall rate from the received signal level at the ground station of direct-to-home (DTH) broadcast satellite links (BSLs) [14][15][16][17][18][19][20]. Hence, taking advantage of the limited cost and ease of installation of the commercial-grade BSL receivers for DTH broadcast, the rationale of our current work consists of effectively merging together the attenuation data coming from both the CML and BSL receivers. ...
... where a n and b n are empirical coefficients (assumed to be known throughout the paper) relying on f n and on the polarization, i.e., horizontal, vertical or circular, [14,26,27]. It is also worth emphasizing that the rain attenuation represents only one of the contributions to the total attenuation affecting the n-th link. ...
... It is also worth emphasizing that the rain attenuation represents only one of the contributions to the total attenuation affecting the n-th link. State-of-the-art works, however, have shown that the rainfall contribution can be reliably extracted from the measurements of the total attenuation [7,14,15]. Furthermore, for the sake of simplicity, we assume the ITU model based on stratiform rain with two layers only, i.e, solid and liquid [24] (A more accurate model considering a third layer, named melting layer between the solid and the liquid layers, was proposed and investigated in [14,16].), as shown in Figure 1, where, for instance, the link 1 is a CML having length L 1 , attenuation A 1 and elevation angle θ 1 = 0, and the link 2 is a BSL with wet path length, i.e., the portion of the path inside the liquid layer, L 2 , attenuation A 2 and elevation angle θ 2 . It can be remarked that the solid layer marginally influences the attenuation, thus explaining the reason why the BSL link length is defined as the wet-path only. ...
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... A disdrometer is a device that detects raindrop size distributions (DSD). In some instances, the terminal velocity of falling hydrometeors can also be used to distinguish between various kinds of precipitation such as raindrops, snowflakes, graupel, or hail over time [66,67]. Figure 4 depicts a typical setup for rain rate measurement using a disdrometer. ...
... Rain gauges are frequently utilized because of their ease of use and dependability, thus lowering installation and maintenance costs. They also provide reliable in-place observations [66]. However, due to their sparse distribution, rain gauges are inadequate for estimating area rainfall, especially in areas with many spatial variabilities, like mountain ranges. ...
... The impact of a cloud on signals is less than that of rain since the attenuation is determined by the cloud's properties, such as its width, depth, and thermal readings (temperature), unlike rain which takes into consideration the communicating system's parameters [141]. According to [142], cloud attenuation can be measured or quantified using the liquid water content and can be mathematically expressed as shown in Equation (66): (66) where is the liquid water content, is the angle of elevation, and cloud-specific attenuation coefficient, which can be expressed mathematically as shown in Equation (67): ...
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Article
Full-text available
  • Sep 2022
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... The symbol error probability can be found as a function of the attenuation. Attenuation as a function of rain rate has been widely calculated and measured [7][8][9][10][11][12][13][14][15][16], with the standard statistical method being the ITU-R recommendations [17][18][19], where we focus on outdoor long-distance communication as relevant to satellite-ground links. The challenge is that the symbol error probability is a non-linear function in terms of signal-to-noise ratio and attenuation, which is correlated with the rain rate. ...
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Article
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... The interpolation for the signal before and after precipitation has been used to obtain the attenuation baseline for the rainy periods in many works [14,15]. The slow Kalman tracker provides the last dry baseline and it is used as an initial reference for baseline determination [16]. Many researchers have utilized machine learning techniques to solve the first issue, and those techniques outperformed the traditional ones. ...
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Full-text available
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... At this time, the microwave rain attenuation can be obtained by using the corresponding extraction algorithm. Finally, the average rain rate on the path of ESL can be obtained by the calculation model between microwave rain attenuation and rainfall [38]. Next, a detailed analysis of the radiation transfer process of ESL is presented. ...
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Full-text available
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... Thus, resulting in substantial path loss and severe degradation in signal coverage and quality of service [14][15][16][17][18][19][20][21]. In order to address this problem, estimating rain rate attenuation will enable terrestrial radio and microwave network planners to determine the type of diversity techniques to explore to combat or compensate for it during and after antenna deployment [22][23][24][25]. ...
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Full-text available
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Article
Full-text available
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Article
Full-text available
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Article
Full-text available
  • May 2015
This study proposes a method based on the use of a set of commercial satellite-to-Earth microwave links to rebuild finescale rainfall fields. Such microwave links exist all over the world and can be used to estimate the integrated rain attenuation over the links’ first 5–7 km with a very high temporal resolution (10 s in the present case). The retrieval algorithm makes use of a four-dimensional variational data assimilation (4DVAR) method involving a numerical advection scheme. The advection velocity is recovered from the observations or from radar rainfall fields at successive time steps. This technique has been successively applied to simulated 2D rain maps and to real data recorded in the autumn of 2013 during the Hydrological Cycle in the Mediterranean Experiment (HyMeX), with one sensor receiving microwave signals from four different satellites. The performance of this system is assessed and is compared to an operational Météo-France radar and a network of 10 rain gauges. Because of the limitations of the propagation model, this study is limited to the events with strong advective characteristics (four out of eight recorded events). For these events (only), the method produces rainfall fields that are highly correlated with the radar maps at spatial resolutions greater than . The point-scale results are also satisfactory for temporal resolutions greater than 10 min (mean correlation with rain gauge data equal to approximately 0.8, similar to the correlation between radar and rain gauge data). This method can also be adapted to the fusion of a rain gauge with microwave link measurements and, through the use of several sensors, it has the potential of being applied to larger areas.
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A Field Study of Pixel-Scale Variability of Raindrop Size Distribution in the Mid-Atlantic Region
Article
  • Jan 2016
The spatial variability of parameters of the raindrop size distribution and its derivatives is investigated through a field study where collocated Particle Size and Velocity (Parsivel2) and two-dimensional video disdrometers were operated at six sites at Wallops Flight Facility, Virginia, from December 2013 to March 2014. The three-parameter exponential function was employed to determine the spatial variability across the study domain where the maximum separation distance was 2.3 km. The nugget parameter of the exponential function was set to 0.99 and the correlation distance d0 and shape parameter s0 were retrieved by minimizing the root-mean-square error, after fitting it to the correlations of physical parameters. Fits were very good for almost all 15 physical parameters. The retrieved d0 and s0 were about 4.5 km and 1.1, respectively, for rain rate (RR) when all 12 disdrometers were reporting rainfall with a rain-rate threshold of 0.1 mm h-1 for 1-min averages. The d0 decreased noticeably when one or more disdrometers were required to report rain. The d0 was considerably different for a number of parameters (e.g., mass-weighted diameter) but was about the same for the other parameters (e.g., RR) when rainfall threshold was reset to 12 and 18 dBZ for Ka- and Ku-band reflectivity, respectively, following the expected Global Precipitation Measurement mission's spaceborne radar minimum detectable signals. The reduction of the database through elimination of a site did not alter d0 as long as the fit was adequate. The correlations of 5-min rain accumulations were lower when disdrometer observations were simulated for a rain gauge at different bucket sizes.
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Rainfall measurements using satellite downlink attenuation
Conference Paper
  • Jul 2014
The attenuation of a commercial satellite link signal at Ku-band is used for estimating rainfall rate along the link path. Comparisons with rainfall accumulations obtained using simultaneous radar measurements along the same path show good agreement. This method can potentially be used to complement other rainfall accumulation measurements obtained with radar and rain gauges in urban settings and areas with complex terrain.
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Improvement of vertical profiles of raindrop size distribution from micro rain radar using 2D video disdrometer measurements
Article
A measurement scheme aimed at investigating precipitation properties based on collocated disdrometer and profiling instruments is used in many experimental campaigns. Raindrop size distribution (RSD) estimated by disdrometer is referred to the ground level; the collocated profiling instrument is supposed to provide complementary estimation at different heights of the precipitation column above the instruments. As part of the Special Observation Period 1 of the HyMeX (Hydrological Cycle in the Mediterranean Experiment) project, conducted between 5 September and 6 November 2012, a K-band vertically pointing micro rain radar (MRR) and a 2D video disdrometer (2DVD) were installed close to each other at a site in the historic center of Rome (Italy). The raindrop size distributions collected by 2D video disdrometer are considered to be fairly accurate within the typical sizes of drops. Vertical profiles of raindrop sizes up to 1085mare estimated fromthe Doppler spectra measured by themicro rain radarwith a height resolution of 35 m. Several issues related to verticalwinds, attenuation correction, Doppler spectra aliasing, and range-Doppler ambiguity limit the performance of MRR in heavy precipitation or in convection, conditions that frequently occur in late summer or in autumn in Mediterranean regions. In this paper,MRR Doppler spectra are reprocessed, exploiting the 2DVDmeasurements at ground to estimate the effects of vertical winds at 105 m (the most reliable MRR lower height), in order to provide a better estimation of vertical profiles of raindrop size distribution fromMRR spectra. Results showthat the reprocessing procedure leads to a better agreement between the reflectivity computed at 105 m from the reprocessed MRR spectra and that obtained fromthe 2DVD data. Finally, vertical profiles ofMRR-estimated RSDs and their relevant moments (namely median volume diameter and reflectivity) are presented and discussed in order to investigate the microstructure of rain both in stratiform and convective conditions.
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