Abstract
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.
Highlights
Floods are one of the most common and destructive natural disasters in the world
The data are the points sampled by CYGNSS along the satellite ellite tracks
Since GNSS signals are circularly polarized, it is necessary to convert the linearly polarized Tb measured by SMAP into circularly polarized Tb [25,36]
Summary
The occurrence of floods has a severe impact on human life and the environment. Climate factors and geographical environment are essential reasons behind flooding. In case of high-intensity, large-scale rainstorms, the affected area is prone to flooding and serious disasters that may even inundate the cities [4,5]. And detailed mapping of the inundated area and the disaster-affected area is essential for post-disaster rescue and restoration. It can help relevant departments better understand the temporal and spatial evolution of this type of disaster, and provide references for the areas that may be affected again [6,7]
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