Soil moisture retrieval at C-band: application to NPOESS/CMIS

One of the difficulties in implementing an AMSR-type soil moisture retrieval technique is that ´a priori´ information used in the retrieval procedure about vegetation optical depth and soil roughness is not easily obtainable: These two parameters or their equivalents must be accurately known because the parameters appear in the exponential of the soil moisture retrieval algorithm. It has been proposed for AMSR that these parameters-will be estimated through ´tuning´ of soil moisture retrieval algorithm during the calibration-validation phase. In the case of NPOESS/CMIS, which has also proposed an AMSR-type retrieval technique for soil moisture estimation, ´tuning´ processes to obtain vegetation optical depth and soil roughness introduces uncertainty and risk to the soil moisture data product for the operational program. In this paper, an alternative soil moisture retrieval technique is presented. It is based on ratioing of the horizontal and vertical brightness temperature.