Soil moisture evaluation using multi-temporal synthetic aperture radar (SAR) in semiarid rangeland

• Published in: Agricultural and forest meteorology 2000-11, Vol.105 (1), p.69-80
• Main Authors: Susan Moran, M, Hymer, Daniel C, Qi, Jiaguo, Sano, Edson E
• Format: Article
• Language: English
• Subjects: Semiarid rangeland; Soil moisture; Synthetic aperture radar
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/S0168-1923(00)00189-1

There have been several efforts to utilize satellite-based synthetic aperture radar (SAR) measurements to determine surface soil moisture (to 5 cm) conditions of rangeland regions. The results have been mixed since the relation between the SAR signal and surface soil moisture is confounded by variations in topographic features, surface roughness and vegetation density. We designed an experiment to investigate the sensitivity of C-band SAR backscatter ( σ 0) to surface soil moisture ( θ s) in a semiarid rangeland and to test a data-fusion approach based on both optical (Landsat TM) and radar (ERS-2 SAR) measurements to improve regional estimates of surface soil moisture content. The data-fusion approach [Sano, E.E. 1997. Sensitivity analysis of C- and Ku-band synthetic aperture radar data to soil moisture content in a semiarid regions. Ph.D. Dissertation. University of Arizona, AZ] utilized the difference between dry- and wet-season SAR σ 0 to normalize roughness effects, and utilized surface reflectance in optical wavelengths to account for differences in vegetation density. We focused the study on three flat, uniformly vegetated sites of known surface roughness, monitored variations in surface soil moisture, vegetation density and SAR signal over time, and obtained eight optical/SAR image pairs throughout the dry and wet seasons. For these sparsely vegetated sites during this dry year (1997), we found that the SAR signal was not significantly attenuated by sparse green vegetation cover ( green leaf area index