The effect of radar configuration on effective correlation length

Soil moisture retrieval from Synthetic Aperture Radar (SAR) over bare soil using the Integral Equation Model (IEM) has not been fully operational for natural conditions, due mainly to the failure of roughness parameterization. Recently, increasing interest has been drawn to improve soil moisture retrieval accuracy of the IEM by introducing an effective correlation length l_eff. However, its behavior under different radar configurations has not been well studied using in-situ observations. This paper demonstrates the effect of radar configuration (polarization, incidence angle and frequency) on l_eff using the satellite SAR data available at multiple frequencies, together with coincident ground measurements collected during the SMAPEx-5 airborne field experiment. The results show i) different polarizations had the same l_eff values; ii) larger l_eff values were obtained from lower incidence angle observations over the same location, and iii) L-band tends to have larger l_eff values than C- and X-bands, whereas the C- and X-bands had similar l_eff values.