scholarly journals Daily Flood Monitoring Based on Spaceborne GNSS-R Data: A Case Study on Henan, China

2021 ◽  
Vol 13 (22) ◽  
pp. 4561
Author(s):  
Wentao Yang ◽  
Fan Gao ◽  
Tianhe Xu ◽  
Nazi Wang ◽  
Jinsheng Tu ◽  
...  
Keyword(s):  
Satellite System ◽  
Daily Basis ◽  
System Level ◽  
High Temporal Resolution ◽  
Specific Situation ◽  
Flood Hazards ◽  
Science Data ◽  
Spatiotemporal Resolution ◽  
Surface Reflectivity ◽  
Global Navigation Satellite

Flood is a kind of natural disaster that is extremely harmful and occurs frequently. To reduce losses caused by the hazards, it is urgent to monitor the disaster area timely and carry out rescue operations efficiently. However, conventional space observers cannot achieve sufficient spatiotemporal resolution. As spaceborne GNSS-R technique can observe the Earth’s surface with high temporal and spatial resolutions; and it is expected to provide a new solution to the problem of flood hazards. During 19–21 July 2021, Henan province, China, suffered a catastrophic flood and urban waterlogging. In order to test the feasibility of flood disaster monitoring on a daily basis by using GNSS-R observations, the CYGNSS (Cyclone Global Navigation Satellite System) Level 1 Science Data were processed for a few days before and after the flood to obtain surface reflectivity by correcting the analog power. Afterwards, the flood was monitored and mapped daily based on the analysis of changes in surface reflectivity from spaceborne GNSS-R mission. The results were evaluated based on the image from MODIS (Moderate Resolution Imaging Spectroradiometer) data, and compared with the observations of SMAP (Soil Moisture Active Passive) in the same period. The results show that the area with high CYGNSS reflectivity corresponds to the flooded area monitored by MODIS, and it is also in high agreement with SMAP. Moreover, CYGNSS can achieve more detailed mapping and quantification of the inundated area and the duration of the flood, respectively, in line with the specific situation of the flood. Thus, spaceborne GNSS-R technology can be used as a method to monitor floods with high temporal resolution.

scholarly journals Assessment of Sampling Effects on Various Satellite-Derived Integrated Water Vapor Datasets Using GPS Measurements in Germany as Reference

2020 ◽  
Vol 12 (7) ◽  
pp. 1170 ◽  
Author(s):  
Cintia Carbajal Henken ◽  
Lisa Dirks ◽  
Sandra Steinke ◽  
Hannes Diedrich ◽  
Thomas August ◽  
...  
Keyword(s):  
Water Vapor ◽  
Pairwise Comparison ◽  
Weather Conditions ◽  
Satellite System ◽  
High Temporal Resolution ◽  
Data Sets ◽  
Frequency Distributions ◽  
Temporal Sampling ◽  
Global Navigation Satellite ◽  
Satellite Instruments

Passive imagers on polar-orbiting satellites provide long-term, accurate integrated water vapor (IWV) data sets. However, these climatologies are affected by sampling biases. In Germany, a dense Global Navigation Satellite System network provides accurate IWV measurements not limited by weather conditions and with high temporal resolution. Therefore, they serve as a reference to assess the quality and sampling issues of IWV products from multiple satellite instruments that show different orbital and instrument characteristics. A direct pairwise comparison between one year of IWV data from GPS and satellite instruments reveals overall biases (in kg/m 2 ) of 1.77, 1.36, 1.11, and −0.31 for IASI, MIRS, MODIS, and MODIS-FUB, respectively. Computed monthly means show similar behaviors. No significant impact of averaging time and the low temporal sampling on aggregated satellite IWV data is found, mostly related to the noisy weather conditions in the German domain. In combination with SEVIRI cloud coverage, a change of shape of IWV frequency distributions towards a bi-modal distribution and loss of high IWV values are observed when limiting cases to daytime and clear sky. Overall, sampling affects mean IWV values only marginally, which are rather dominated by the overall retrieval bias, but can lead to significant changes in IWV frequency distributions.

scholarly journals AIOSAT - Autonomous Indoor & Outdoor Safety Tracking System

2019 ◽  
Vol 26 (1) ◽  
pp. 21-32
Author(s):  
Iñigo Adin ◽  
Paul Zabalegui ◽  
Alejandro Perez ◽  
Jaione Arrizabalaga ◽  
Jon Goya ◽  
...  
Keyword(s):  
Rural Areas ◽  
Tracking System ◽  
Dead Reckoning ◽  
Wide Band ◽  
Satellite System ◽  
System Level ◽  
Horizon 2020 ◽  
Rescue Workers ◽  
Global Navigation Satellite ◽  
Map Data

Abstract Even though satellite-based positioning increases rescue workers’ safety and efficiency, signal availability, reliability, and accuracy are often poor during fire operations, due to terrain formation, natural and structural obstacles or even the conditions of the operation. In central Europe, the stakeholders report a strong necessity to complement the location for mixed indoor-outdoor and GNSS blocked scenarios. As such, location information often needs to be augmented. For that, European Global Navigation Satellite System Galileo could help by improving the availability of the satellites with different features. Moreover, a multi-sensored collaborative system could also take advantage of the rescue personnel who are already involved in firefighting and complement the input data for positioning. The Autonomous Indoor & Outdoor Safety Tracking System (AIOSAT) is a multinational project founded through the Horizon 2020 program, with seven partners from Spain, Netherlands and Belgium. It is reaching the first year of progress (out of 3) and the overarching objective of AIOSAT system is to advance beyond the state of the art in tracking rescue workers by creating a high availability and high integrity team positioning and tracking system. On the system level approach, this goal is achieved by fusing the GNSS, EDAS/EGNOS, pedestrian dead reckoning and ultra-wide band ranging information, possibly augmented with map data. The system should be able to work both inside buildings and rural areas, which are the test cases defined by the final users involved in the consortium and the advisory board panel of the project

scholarly journals Blind Spoofing GNSS Constellation Detection Using a Multi-Antenna Snapshot Receiver

Sensors ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 5439
Author(s):  
Johannes Rossouw van der Merwe ◽  
Alexander Rügamer ◽  
Wolfgang Felber
Keyword(s):  
Clustering Algorithms ◽  
Satellite System ◽  
System Level ◽  
Navigation Satellite ◽  
Positioning Systems ◽  
Test Setup ◽  
Counter Method ◽  
Eigen Decomposition ◽  
Global Navigation Satellite ◽  
Gnss Constellation

Spoofing of global navigation satellite system (GNSS) signals threatens positioning systems. A counter-method is to detect the presence of spoofed signals, followed by a warning to the user. In this paper, a multi-antenna snapshot receiver is presented to detect the presence of a spoofing attack. The spatial similarities of the array steering vectors are analyzed, and different metrics are used to establish possible detector functions. These include subset methods, Eigen-decomposition, and clustering algorithms. The results generated within controlled spoofing conditions show that a spoofed constellation of GNSS satellites can be successfully detected. The derived system-level detectors increase performance in comparison to pair-wise methods. A controlled test setup achieved perfect detection; however, in real-world cases, the performance would not be as ideal. Some detection metrics and features for blind spoofing detecting, with an array of antennas, are identified, which opens the field for future advanced multi-detector developments.

Water vapour trends in Switzerland from radiometry, FTIR and GNSS ground stations

2020 ◽  
Author(s):  
Leonie Bernet ◽  
Elmar Brockmann ◽  
Thomas von Clarmann ◽  
Niklaus Kämpfer ◽  
Emmanuel Mahieu ◽  
...  
Keyword(s):  
Water Vapour ◽  
Temporal Resolution ◽  
Regional Climate ◽  
Satellite System ◽  
Reanalysis Data ◽  
High Temporal Resolution ◽  
Integrated Water Vapour ◽  
Global Navigation Satellite ◽  
Increasing Temperature ◽  
Gnss Data

<div> <div>Water vapour in the atmosphere is not only a strong greenhouse gas, but also affects many atmospheric processes such as the formation of clouds and precipitation. With increasing temperature, Integrated Water Vapour (IWV) is expected to increase. Analysing how atmospheric water vapour changes in time is therefore important to monitor ongoing climate change. To determine whether IWV increases in Switzerland as expected, we asses IWV trends from a tropospheric water radiometer (TROWARA) in Bern, from a Fourier transform infrared (FTIR) spectrometer at Jungfraujoch and from the Swiss network of ground-based Global Navigation Satellite System (GNSS) stations. In addition, trends are assessed from reanalysis data, using the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) and the Modern-Era Retrospecitve Analysis for Research and Applications (MERRA-2).</div> <div>Ground-based GNSS data are well suited for IWV trends due to their high temporal resolution and the spatially dense networks. However, they are highly sensitvie to instrumental changes and care has to be taken when determining GNSS based trends. We therefore use a straightforward trend method to account for jumps in the GNSS data when instrumental changes were performed.</div> <div>Our data show mostly positive IWV trends between 2 and 5% per decade in Switzerland. GNSS trends are significant for some stations and the significance has the tendency to increase with altitude. Further, we found that IWV scales on average to lower tropospheric temperatures as expected, except in winter. However, the correlation between IWV and temperature based on reanalysis data is spatially incoherent. Besides our positive IWV trends, we found a good agreement of radiometer, GNSS and reanalysis data in Bern. Further, we found a dry bias of the FTIR compared to GNSS data at Jungfraujoch, due to the restriction of FTIR to clear-sky conditions. Our results are generally consistent with the positive water vapour feedback in a warming climate. We show that ground-based GNSS networks provide a valuable source for regional climate monitoring with high spatial and temporal resolution, but homogeneously reprocessed data and advanced trend techniques are needed to account for data jumps.</div> </div>

scholarly journals Review on the Role of GNSS Meteorology in Monitoring Water Vapor for Atmospheric Physics

2021 ◽  
Vol 13 (12) ◽  
pp. 2287
Author(s):  
Javier Vaquero-Martínez ◽  
Manuel Antón
Keyword(s):  
Water Vapor ◽  
Low Cost ◽  
Satellite System ◽  
Climate System ◽  
Atmospheric Water Vapor ◽  
Tropospheric Delay ◽  
High Temporal Resolution ◽  
Atmospheric Water ◽  
Gnss Meteorology ◽  
Global Navigation Satellite

After 30 years since the beginning of the Global Positioning System (GPS), or, more generally, Global Navigation Satellite System (GNSS) meteorology, this technique has proven to be a reliable method for retrieving atmospheric water vapor; it is low-cost, weather independent, with high temporal resolution and is highly accurate and precise. GNSS ground-based networks are becoming denser, and the first stations installed have now quite long time-series that allow the study of the temporal features of water vapor and its relevant role inside the climate system. In this review, the different GNSS methodologies to retrieve atmospheric water vapor content re-examined, such as tomography, conversion of GNSS tropospheric delay to water vapor estimates, analyses of errors, and combinations of GNSS with other sources to enhance water vapor information. Moreover, the use of these data in different kinds of studies is discussed. For instance, the GNSS technique is commonly used as a reference tool for validating other water vapor products (e.g., radiosounding, radiometers onboard satellite platforms or ground-based instruments). Additionally, GNSS retrievals are largely used in order to determine the high spatio-temporal variability and long-term trends of atmospheric water vapor or in models with the goal of determining its notable influence on the climate system (e.g., assimilation in numerical prediction, as input to radiative transfer models, study of circulation patterns, etc.).

scholarly journals Validating HY-2A CMR precipitable water vapor using ground-based and shipborne GNSS observations

2020 ◽  
Vol 13 (9) ◽  
pp. 4963-4972
Author(s):  
Zhilu Wu ◽  
Yanxiong Liu ◽  
Yang Liu ◽  
Jungang Wang ◽  
Xiufeng He ◽  
...  
Keyword(s):  
Water Vapor ◽  
Microwave Radiometer ◽  
Precipitable Water ◽  
Satellite System ◽  
Precipitable Water Vapor ◽  
Tropospheric Delay ◽  
High Temporal Resolution ◽  
International Gnss Service ◽  
Global Navigation Satellite ◽  
Gnss Observations

Abstract. The calibration microwave radiometer (CMR) on board the Haiyang-2A (HY-2A) satellite provides wet tropospheric delay correction for altimetry data, which can also contribute to the understanding of climate system and weather processes. The ground-based global navigation satellite system (GNSS) provides precise precipitable water vapor (PWV) with high temporal resolution and could be used for calibration and monitoring of the CMR data, and shipborne GNSS provides accurate PWV over open oceans, which can be directly compared with uncontaminated CMR data. In this study, the HY-2A CMR water vapor product is validated using ground-based GNSS observations of 100 International GNSS Service (IGS) stations along the global coastline and 56 d shipborne GNSS observations over the Indian Ocean. The processing strategy for GNSS data and CMR data is discussed in detail. Special efforts were made in the quality control and reconstruction of contaminated CMR data. The validation result shows that HY-2A CMR PWV agrees well with ground-based GNSS PWV with 2.67 mm as the root mean square (rms) within 100 km. Geographically, the rms is 1.12 mm in the polar region and 2.78 mm elsewhere. The PWV agreement between HY-2A and shipborne GNSS shows a significant correlation with the distance between the ship and the satellite footprint, with an rms of 1.57 mm for the distance threshold of 100 km. Ground-based GNSS and shipborne GNSS agree with HY-2A CMR well.

Assessment Models and Rules of GNSS Interoperability

2013 ◽  
Vol 846-847 ◽  
pp. 808-811
Author(s):  
Wei Wang ◽  
Cheng Cai Lv ◽  
Xin Li
Keyword(s):  
Global Navigation Satellite System ◽  
Satellite System ◽  
System Level ◽  
Navigation Satellite ◽  
Weighted Sum ◽  
Dilution Of Precision ◽  
Satellite Systems ◽  
System Integrity ◽  
Simulation Results ◽  
Global Navigation Satellite

Global Navigation Satellite System (GNSS) interoperability could make use of the information from different navigation satellite systems. To estimate GNSS interoperability at the system level, an innovative assessment algorithm was presented in this paper. First of all, three assessment parameters, namely, Dilution Of Precision (DOP), Navigation Satellite System Precision (NSSP) and Navigation Satellite System Integrity (NSSI) were introduced. Secondly, availability and continuity of the assessment parameters were adopted to quantify the GNSS performance. A further step was then taken to focus on the assessment rule for GNSS performance by employing the weighted sum of availability and continuity. Simulation results demonstrate that GNSS performance could be improved significantly by interoperability.

scholarly journals Advances of SBAS authentication technologies

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Ying Chen ◽  
Weiguang Gao ◽  
Xiao Chen ◽  
Ting Liu ◽  
Cheng Liu ◽  
...  
Keyword(s):  
Digital Signature ◽  
Satellite System ◽  
System Level ◽  
The Public ◽  
Interface Control ◽  
Digital Signature Algorithm ◽  
Geo Satellites ◽  
Authentication Security ◽  
Global Navigation Satellite ◽  
The Impact

AbstractSatellite Based Augmentation System (SBAS) provides the corrections and integrity information to users, but as its signal format is opened to the public and Global Navigation Satellite System (GNSS) spoofing technology becomes more realistic, more feasible and cheaper. It's foreseeable that there will be risks of spoofing threats against SBAS in the future. SBAS signal authentication technology provides a system-level solution to spoofing threats by adding special markers to SBAS signals so that receivers can verify whether the SBAS signals are from the on-orbit Geostationary Earth Orbit (GEO) satellites or whether the signal information has been forged and tampered with. First, this article introduces the existing anti-spoofing methods that can be applied to SBAS, especially the Elliptic Curve Digital Signature Algorithm (ECDSA) and Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocols. Then it discusses four possible solutions in a combination with the existing SBAS Interface Control Document (ICD). Two main Key Performance Indicators (KPIs), Time Between Authentication (TBA) and Authentication Latency (AL), obtained in the four main scenarios are compared. By analyzing the EGNOS Authentication Security Testbed (EAST) test simulation results of European Geostationary Navigation Overlay Service (EGNOS) in Europe, the impact of SBAS after joining the authentication service is obtained.

scholarly journals Low-Cost GPS Receivers for the Monitoring of Sunflower Cover Dynamics

2017 ◽  
Vol 2017 ◽  
pp. 1-9
Author(s):  
Mehrez Zribi ◽  
Erwan Motte ◽  
Pascal Fanise ◽  
Walid Zouaoui
Keyword(s):  
Water Content ◽  
Low Cost ◽  
Ground Truth ◽  
Satellite System ◽  
Daily Basis ◽  
Empirical Modeling ◽  
Test Field ◽  
Signal Attenuation ◽  
Vegetation Water ◽  
Global Navigation Satellite

The aim of this research is to analyze the potential use of Global Navigation Satellite System (GNSS) signals for the monitoring of in situ vegetation characteristics. An instrument, based on the use of a pair of low-cost receivers and antennas, providing continuous measurements of all the available Global Positioning System (GPS) satellite signals is proposed for the determination of signal attenuation caused by a sunflower cover. Experimental campaigns with this instrument, combined with ground truth measurements of the vegetation, were performed over a nonirrigated sunflower test field for a period of more than two months, corresponding to a significant portion of the vegetation cycle. A method is proposed for the analysis of the signal attenuation data as a function of elevation and azimuth angles. A high correlation is observed between the vegetation’s water content and the GPS signals attenuation, and an empirical modeling is tested for the retrieval of signal behavior as a function of vegetation water content (VWC). The VWC was estimated from GNSS signals on a daily basis, over the full length of the study period.

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