COMPARISON OF THE DOBSON MODEL WITH OTHER DIELECTRIC MODELS AT THE C-BAND MICROWAVE BAND

This study focuses on a dielectric model for wet soils that relates the complex permittivity and water content of bulk wet soils to obtain soil moisture retrievals from satellite observations. Contrary to the earlier examinations that have been made for the Soil Moisture and Ocean Salinity (SMOS) mission of the European Satellite Agency (ESA) at 1.4 GHz (L-band microwave range), this study targets 6.9 GHz (C-band) of the Advanced Microwave Scanning Radiometer 2 (AMSR2) of the Japan Aerospace Exploration Agency (JAXA), considering the frequency dependency of the dielectric behavior of wet soils. The Dobson model is the most widely used dielectric model and is currently used in JAXA’s standard algorithm. ESA also used the Dobson model, but it switched to using the Mironov model in 2012 for its operational algorithm. In addition to these two models, the Wang-Schmugge model and our proposed model were numerically analyzed to clarify the effect on soil moisture retrievals by replacing the dielectric model from Dobson with another model at 6.9 GHz. Large differences were observed between the Dobson and Mironov models, especially for the soil types that contain large quantities of sand or clay. The Wang-Schmugge model showed similar estimates to those of the Mironov model but with a large difference in the estimated amount and permittivity of bound soil water. The estimated wet-soil permittivity by our proposed model was smaller than those of other models in many cases, slightly for temperate soils and significantly for tropical soils. Both the amount and permittivity of bound water in the proposed model were smaller than those of the Mironov and Wang-Schmugge models. The quantification of the amount and permittivity of bound water was shown to be the key in the dielectric model, and further validation with soil samples, especially with tropical samples, is necessary.