The effect of measurement error and confusion from vegetation on passive microwave estimates of soil moisture

When using passive microwave sensors to estimate soil moisture it is important to understand the sensitivity of the estimate to (1) the effects of confusion due to surface roughness and vegetation and (2) the effect of measurement error due to noise. The sensitivity of error in soil moisture estimates to passive microwave measurement error as a function of vegetation is presented using a simple model and measurements. Roughness confusion is not considered. The direct problem is defined as investigating the sensor response as the dependent variable to the parameter of interest while the inverse problem uses the parameter of interest as the dependent variable. The inverse method must be used for operational remote sensing applications. It is shown that this subtle difference becomes very important when both confusion and measurement error are considered. A methodology is also presented whereby the sensitivity to measurement error attributed to vegetation can be estimated from the perpendicular vegetation index (PVI).