An empirical soil moisture retrieval model for dual-polarimetric L-band SAR imaging, the ALOS-2 standard observation, is being developed. The model, based on empirical relations between ALOS/PALSAR and Pi-SAR-L2 observations and ground measurements, can correct for the disturbing effects caused by surface roughness or vegetation cover. In this paper we focus on airborne campaigns carried out over the Sendai area, Japan, in 2013 and 2014. In situ surface parameters (soil moisture and surface roughness) were measured on bare soil and under rice canopy. Using roughness and biomass corrections the SAR derived soil moisture estimates yield an accuracy of 5.9 Vol.-% RMSE. The results indicate that the proposed approach, which was mainly parameterized in test sites in Germany, can also work in different geographic regions.