Abstract
In a perspective to develop an inversion approach for estimating surface soil moisture of crop fields from Sentinel-1/2 data (radar and optical sensors), the Water Cloud Model (WCM) was calibrated from C-band Synthetic Aperture Radar (SAR) data and Normalized Difference Vegetation Index (NDVI) values collected over crops fields and grasslands. The soil contribution that depends on soil moisture and surface roughness (in addition to SAR instrumental parameters) was simulated using the physical backscattering model IEM (Integral Equation Model). The vegetation descriptor used in the WCM is the NDVI because it can be directly calculated from optical images. A large dataset consisting of radar backscattered signal in Vertical transmit and Vertical receive (VV) and Vertical transmit and Horizontal receive (VH) polarizations with wide range of incidence angle, soil moisture, surface roughness, and NDVI-values was used. It was collected over two agricultural study sites. Results show that the soil contribution to the total radar backscattered signal is lower in VH than in VV because VH is more sensitive to vegetation cover. Thus, the use of VH alone or in addition to VV for retrieving the soil moisture is not advantageous in presence of well-developed vegetation cover.
Highlights
IntroductionThe new C-band radar satellites Sentinel-1A (launched on 3 April 2014) and Sentinel-1B (launched on April 2016), in addition to the optical satellites Sentinel-2A and Sentinel-2B (launched on June 2015 and 7 March 2017, respectively), provide free and open access data for the whole globe with high spatial and temporal resolutions (six days with Sentinel-1 satellites and five days with Sentinel-2 satellites at 10 m spatial resolution)
The new C-band radar satellites Sentinel-1A and Sentinel-1B, in addition to the optical satellites Sentinel-2A and Sentinel-2B, provide free and open access data for the whole globe with high spatial and temporal resolutions
It is due to the low sensitivity of Normalized Difference Vegetation Index (NDVI) to vegetation parameters (LAI, VWC . . . ) in the case of high values of vegetation parameters [21,22,23]
Summary
The new C-band radar satellites Sentinel-1A (launched on 3 April 2014) and Sentinel-1B (launched on April 2016), in addition to the optical satellites Sentinel-2A and Sentinel-2B (launched on June 2015 and 7 March 2017, respectively), provide free and open access data for the whole globe with high spatial and temporal resolutions (six days with Sentinel-1 satellites and five days with Sentinel-2 satellites at 10 m spatial resolution). This availability of both Sentinel-1 and Sentinel-2 satellites allows the coupling of SAR (Synthetic Aperture Radar) and optical data for operational soil moisture mapping at field scale.
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