Soil Moisture Estimation by Combining L-Band Brightness Temperature and Vegetation Related Information

Abstract

Passive radiometry at L-band has been widely accepted as one of the most promising techniques for monitoring soil moisture content (SMC). However, with vegetation cover, the scatter and attenuation of microwave signals by vegetation make the discrimination of SMC related signal complicated. To improve SMC estimate, this study proposed the combined use of L-band brightness temperature (TB) and optical remote sensing data to take into account the effect of vegetation. The normalized difference infrared index (NDII) and enhanced vegetation index (EVI) were used as proxy for including the effect of vegetation water content and structure. Considering viewing angle effects, TB data were normalized to three different angles (7°, 21.5°, and 38.5°). The model based on the combination of NDII and horizontally polarized TB normalized to 7° produced the best result (R2 = 0.678, RMSE = 0.026 m3/m3). It suggests that involving NDII into the model could significantly improve pasture covered SMC estimation accuracy.