Abstract
The next generation of synthetic aperture radar (SAR) systems could foresee satellite missions based on a geosynchronous orbit (GEO SAR). These systems are able to provide radar images with an unprecedented combination of spatial (≤1 km) and temporal (≤12 h) resolutions. This paper investigates the GEO SAR potentialities for soil moisture (SM) mapping finalized to hydrological applications, and defines the best compromise, in terms of image spatio-temporal resolution, for SM monitoring. A synthetic soil moisture–data assimilation (SM-DA) experiment was thus set up to evaluate the impact of the hydrological assimilation of different GEO SAR-like SM products, characterized by diverse spatio-temporal resolutions. The experiment was also designed to understand if GEO SAR-like SM maps could provide an added value with respect to SM products retrieved from SAR images acquired from satellites flying on a quasi-polar orbit, like Sentinel-1 (POLAR SAR). Findings showed that GEO SAR systems provide a valuable contribution for hydrological applications, especially if the possibility to generate many sub-daily observations is sacrificed in favor of higher spatial resolution. In the experiment, it was found that the assimilation of two GEO SAR-like observations a day, with a spatial resolution of 100 m, maximized the performances of the hydrological predictions, for both streamflow and SM state forecasts. Such improvements of the model performances were found to be 45% higher than the ones obtained by assimilating POLAR SAR-like SM maps.
Highlights
Within the Earth system science framework, soil moisture (SM) represents a key variable because it directly controls water and energy fluxes between the atmosphere and the land surface [1,2,3]
If results related to hourly discharge data and hourly root zone (RZ)-SD values are jointly considered, it is clear that the assimilation of the GEO synthetic aperture radar (SAR) product GEO-3 with a G value equal to 0.2 provided the highest improvements both on streamflow and SM predictions
This is a demonstration of the potential added value that can be provided by using geosynchronous synthetic aperture radar (GEO SAR)-like SM products with higher spatial resolution (SpR) (100 m) and sub-daily temporal resolution (TeR) (8 h) for hydrological applications
Summary
Within the Earth system science framework, soil moisture (SM) represents a key variable because it directly controls water and energy fluxes between the atmosphere and the land surface [1,2,3]. For this reason, its accurate monitoring is fundamental to a plethora of applications, such as meteorology, agriculture (e.g., irrigation management), hydrology and weather-related risk assessment and forecasting (e.g., floods, landslide, drought) [2,3,4,5,6]. Concerning hydrological applications, the scientific community pointed out the need for a more accurate strategy for SM monitoring at higher spatio-temporal resolutions [3,8]
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