A combined optical-microwave method to retrieve soil moisture over vegetated areas
Une méthode combinée optique-micro-ondes pour restituer l'humidité du sol sur les zones couvertes de végétation
Mattar, C. ; Wigneron, J.-P. ; Sobrino, J.A. ; Novello, N. ; Calvet, Jean-Christophe ; Albergel, C. ; Richaume, P. ; Mialon, A. ; Guyon, D. ; Jimenez-Munoz, J.-C. ; Kerr, Y.
A simple approach for correcting for the effect of vegetation in the estimation of the surface soil moisture (wS) from L-band passive microwave observations is presented in this study. The approach is based on semi-empirical relationships between soil moisture and the polarized reflectivity including the effect of the vegetation optical depth which is parameterized as a function of the normalized vegetation difference index (NDVI). The method was tested against in situ measurements collected over a grass site from 2004 to 2007 (SMOSREX experiment). Two polarizations (horizontal/vertical) and five incidence angles (20°, 30°, 40°, 50°, and 60°) were considered in the analysis. The best wS estimations were obtained when using both polarizations at an angle of 40°. The average accuracy in the soil moisture retrievals was found to be approximately 0.06 m3/m3, improving the estimations by 0.02 m3/m3 with respect to the case in which the vegetation effect is not considered. The results indicate that information on vegetation (through a vegetation index such as NDVI) is useful for the estimation of soil moisture through the semi-empirical regressions.
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