Soil moisture retrieval over grassland using X-band SAR data

The objective of this study was to analyze the sensitivity of radar signal in X-band to irrigated grassland soil conditions. Time series of radar (TerraSAR-X and Cosmo-SkyMed) images were acquired at a high temporal frequency in 2013 over a small agricultural region in South Eastern France. Simultaneously to satellite data acquisitions, ground measurements were conducted during several growing cycles of the grassland in order to monitor evolution in soil and vegetation characteristics. Results show that radar signal is clearly dependent on the soil moisture with a higher sensitivity to soil moisture for biomass lower than 1 kg/m². HH and HV polarizations showed almost similar sensitivity to soil moisture. The penetration depth of the radar wave in X-band was high even for dense and high vegetation: flooded areas were clearly visible on the images with higher detection potential in HH polarization than in HV polarization even for vegetation heights reaching 1 m. These results showed that it is possible to track gravity irrigation and soil moisture variation from SAR X-band images acquired at high spatial resolution and medium incidence angle.