Abstract
This paper investigates a simplified polarimetric decomposition for soil moisture retrieval over agricultural fields. In order to overcome the coherent superposition of the backscattering contributions from vegetation and underlying soils, a simplification of an existing polarimetric decomposition is proposed in this study. It aims to retrieve the soil moisture by using only the surface scattering component, once the volume scattering contribution is removed. Evaluation of the proposed simplified algorithm is performed using extensive ground measurements of soil and vegetation characteristics and the time series of UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar) data collected in the framework of SMAP (Soil Moisture Active Passive) Validation Experiment 2012 (SMAPVEX12). The retrieval process is tested and analyzed in detail for a variety of crops during the phenological stages considered in this study. The results show that the performance of soil moisture retrieval depends on both the crop types and the crop phenological stage. Soybean and pasture fields present the higher inversion rate during the considered phenological stage, while over canola and wheat fields, the soil moisture can be retrieved only partially during the crop developing stage. RMSE of 0.06–0.12 m3/m3 and an inversion rate of 26%–38% are obtained for the soil moisture retrieval based on the simplified polarimetric decomposition.
Highlights
For agricultural fields, soil moisture is an important factor for several physical processes such as water conservation, soil erosion and surface runoff
For soil moisture retrieval using SMAPVEX12 datasets, the present study evaluates the applicability of a simplified version of an existing model-based polarimetric decomposition technique [1] which was developed from Freeman-Durden/Yamaguchi target decomposition methods [10,11]
We present the results obtained from the application of the simplified polarimetric soil moisture retrieval method to the temporal datasets of UAVSAR acquired during SMAPVEX12
Summary
Soil moisture is an important factor for several physical processes such as water conservation, soil erosion and surface runoff. The vegetation layer is modeled and removed using incoherent radiative transfer approach [6]. Such a model considers the total backscattering coefficient as an incoherent sum of the scattering contributions from the vegetation volume scattering, the soil scattering and their interaction. The well-known water-cloud model [7], which is widely used for soil moisture retrieval, is a simple first-order radiative transfer solution which neglects the multiple scattering, and assumes that the vegetation and the underlying soil contributions are incoherently added up. On the other hand, based on the polarimetric SAR measurements, the target decomposition methodologies [10,11,12] are used to remove the vegetation component and estimate the underlying soil moisture from the ground scattering component. The three-component model-based polarimetric decomposition [10] has been adapted [1,2,3] for soil moisture estimation under vegetation
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