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Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR)
Vienna University of Technology, Institute of Photogrammetry and Remote Sensing, Gußhausstraße 27-29, 1040 Vienna, Austria
Vienna University of Technology, Institut für Wasserbau und Ingenieurhydrologie, Karlsplatz 13/222, A-1040 Wien, Vienna, Austria
European Centre for Medium Range Weather Forecasting, Shinfield Park, Reading RG2 9AX, United Kingdom
Department of Geography, University of Salamanca, Cervantes 3, 37002 Salamanca, Spain
University of Munich, Munich, University of Munich, Munich, Department of Geography, Luisenstrasse 37, 80333 Munich, Germany
* Author to whom correspondence should be addressed.
Received: 11 January 2008; Accepted: 19 February 2008 / Published: 21 February 2008
Abstract: The high spatio-temporal variability of soil moisture is the result of atmosphericforcing and redistribution processes related to terrain, soil, and vegetation characteristics.Despite this high variability, many field studies have shown that in the temporal domainsoil moisture measured at specific locations is correlated to the mean soil moisture contentover an area. Since the measurements taken by Synthetic Aperture Radar (SAR)instruments are very sensitive to soil moisture it is hypothesized that the temporally stablesoil moisture patterns are reflected in the radar backscatter measurements. To verify this hypothesis 73 Wide Swath (WS) images have been acquired by the ENVISAT AdvancedSynthetic Aperture Radar (ASAR) over the REMEDHUS soil moisture network located inthe Duero basin, Spain. It is found that a time-invariant linear relationship is well suited forrelating local scale (pixel) and regional scale (50 km) backscatter. The observed linearmodel coefficients can be estimated by considering the scattering properties of the terrainand vegetation and the soil moisture scaling properties. For both linear model coefficients,the relative error between observed and modelled values is less than 5 % and thecoefficient of determination (R2) is 86 %. The results are of relevance for interpreting anddownscaling coarse resolution soil moisture data retrieved from active (METOP ASCAT)and passive (SMOS, AMSR-E) instruments.
Keywords: Soil moisture; SAR; backscatter; scaling; temporal stability
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Wagner, W.; Pathe, C.; Doubkova, M.; Sabel, D.; Bartsch, A.; Hasenauer, S.; Blöschl, G.; Scipal, K.; Martínez-Fernández, J.; Löw, A. Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR). Sensors 2008, 8, 1174-1197.
Wagner W, Pathe C, Doubkova M, Sabel D, Bartsch A, Hasenauer S, Blöschl G, Scipal K, Martínez-Fernández J, Löw A. Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR). Sensors. 2008; 8(2):1174-1197.
Wagner, Wolfgang; Pathe, Carsten; Doubkova, Marcela; Sabel, Daniel; Bartsch, Annett; Hasenauer, Stefan; Blöschl, Günter; Scipal, Klaus; Martínez-Fernández, José; Löw, Alexander. 2008. "Temporal Stability of Soil Moisture and Radar Backscatter Observed by the Advanced Synthetic Aperture Radar (ASAR)." Sensors 8, no. 2: 1174-1197.