Journal of Arid Environments (2001) 49: 449–464 doi:10.1006/jare.2001.0809, available online at http://www.idealibrary.com on Soil water-content and surface roughness retrieval using ERS-2 SAR data in the Negev Desert, Israel Dan G. Blumberg* - & Valentin Freilikher? *Department of Geography and Environmental Development, Ben-Gurion University of the Negev, Be’er Sheva, 84105, Israel ?Department of Physics, Bar-Ilan University, Ramat-Gan, Israel (Received 8 June 2000, accepted 20 February 2001, published electronically 19 July 2001) 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 homo- geneous, 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 backscat- ter 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, explaining ca. 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.  2001 Academic Press Introduction Background The need to make highly efficient use of water resources with the concommitent economic considerations, is one of the most challenging problems facing present day agriculture in arid and semi-arid regions in general, and in the Middle East, in particular. Since this environment is partly arid and partly semi-arid, it requires precision farming in order to retain its viability. Remote sensing is a tool which can rapidly and reliably collect data about a variety of ground conditions. Therefore, it can and should be used for precision agriculture in such regions. This paper deals with a particular aspect of precision agriculture, the ability to map and monitor soil water-content from satellite Corresponding author. Fax:# 972-7-647-2821. E-mail: Blumberg@mail.bgu.ac.il. url:http://www.geog.bgu.ac.il 0140}1963/01/110449#16 $35.00/0  2001 Academic Press