Soil Moisture Measurements by Synthetic Aperture Radar and Scatterometers in the Arid and Semi-arid Environment

Water is a scarce commodity in desert regions; yet, most remote sensing experiments of soil moisture have been conducted in temperate areas. The ability to detect and reliably assess soil moisture in the arid environment has important implications both at the micro scale such as the individual farm and at the macro scale for climate modeling. A series of experiments utilizing an airborne scatterometer operating at P-band were conducted to assess the ability to measure soil moisture over farmlands in the Negev Desert by remote sensing. The soil moisture is determined by measuring the backscattered radar signal at the scatterometer. Results show that in the arid environment of the Negev scatterometer data correlate well with field measured soil water content. The water content values measured were between 2 and 7% (volumetric). Some extreme values were measured at the Ramat Negev experimental farm. A later visit to the farm confirmed a faucet leak at the location of the extensive values (>20%.) We could also detect an increase in water content adjacent to a sewer reclemation pond at Mashabei Sadeh. A second series of experiments were conducted with spaceborne synthetic aperture radar using the ERS-2 SAR system. This system is single wavelength operating at C-band HH polarization. We used two images to achieve two incidence angles for the same site. Results show that 90% of the variance in radar backscatter over individual fields can be explained using soil water and surface roughness measurements.