Airborne GPS bistatic radar soil moisture measurements during SMEX02

To further investigate the potential for remotely sensing soil moisture using the L-band GPS bistatic radar concept, a GPS bistatic radar participated for the first time in airborne measurements during the Soil Moisture Experiment 2002 (SMEX02) in Ames, Iowa. A 12 channel GPS navigation receiver was modified to perform bistatic radar measurements and mounted on the JPL PALS instrument. The reflected GPS signal-to-noise ratio measurements generated a ground track which was sensitive to the surface characteristics. Assuming surface roughness and vegetation cover to be constants over the duration of the study period, the temporal changes in the measured signals were suspected to be proportional to varying soil moisture content. The bistatic signal measurements were interpolated to a UTM grid to produce daily maps of relative change of surface soil moisture over the study region. The maps of the study region showed a transition from very dry surface soil moisture conditions to very wet conditions following precipitation events occurring in the middle of the study period. Additionally, the maps showed sensitivity to localized rainfall in areas without precipitation. The scattered signal measurements were also compared with in situ soil moisture measurements at 32 field sites and found to follow the general soil moisture trend as a function of time. These positive initial results from the first controlled experiment of GPS bistatic radar foe measuring soil moisture were encouraging. Additional analyses with the present data set and comparison with other remote sensing instruments (PALS) are planned as well as participation in future campaigns.