Soil water-content and surface roughness retrieval using ERS-2 SAR data in the Negev Desert, Israel

A study was conducted to explore the use of ERS-2 synthetic aperture radar (SAR) data to assess the soil water-content of agricultural farmlands in the Negev Desert, Israel. The ERS-2 data were acquired using the Israel Space Agency (ISA) receiving station operated by Israel Aircraft Industries. Field measurements of volumetric and gravimetric soil water-content and surface roughness were conducted, concurrent with the deployment of well-measured corner reflectors in the field for calibration and geo-rectification of the radar data. Results show that for individual fields, where surface roughness is homogeneous, the radar backscatter cross-section correlates well with the soil water-content component. For mapping water-content over several fields, the surface roughness must be incorporated into any model that correlates radar backscatter with soil water-content. To solve for roughness and soil water-content, two ERS images with different look directions were acquired, providing two different radar signatures. An empirical model was derived to assess water-content conditions, explainingca. 90% of the backscatter variation using water-content, roughness, and incidence angle. Because it is empirical, the model holds locally and would not be universally true. Therefore, the approach should be tested elsewhere.