Use of ERS-1 SAR data for soil moisture assessment

This study has been carried out for grassland and surrounding agriculture in the western part of Poland. ERS-1 SAR data obtained from ESA for Pilot Project PL-4 for the 1992 and 1993 growing seasons have been analyzed and compared to ground measurements collected over the test site. The impact of various ground truth variables on backscatter signatures was examined to develop the method of soil moisture assessment over agricultural crops and grassland. The effectiveness of deriving a backscattering coefficient averaged over different sized blocks of ERS-1 SAR image pixels and subsequent comparison to measured soil moisture was examined. Two-way character of backscatter-soil moisture relationship has been noticed due to succeeding development stages of crops. Good negative correlation between backscatter and soil moisture occurred for stubble and for short grass (LAI from 0.5 up to 1.5) and for early and final stages of root crops and maize. Good positive correlation between backscatter and soil moisture occurred for different crops as: tall grass (LAI above 3) spring wheat, rape and root crops in their full green mass. It was considered that the relationship between backscattering coefficient and soil moisture is strongly dependent on surface roughness which was characterized by leaf area index (LAI) or height of the vegetation values.