Evaluation of the AIRSAR system for soil moisture analysis

In many disciplines of science, soil moisture content (SMC) is an important parameter for modeling of dynamic water cycles. In this study, the sensitivity of the backscattering coefficient was investigated in conjunction with the soil moisture content of vegetation-covered (corn) fields. As part of the MAC-Europe campaign in July 1991, the NASA/JPL three frequency polarimetric AIRSAR system collected data over a test site at Oberpfaffenhofen in Germany. The AIRSAR overflight at Oberpfaffenhofen was complemented by intensive ground truth measurements. The study was carried out with a monotemporal data set. The sampled cornfields are nearly in the same SAR incidence angle range (≈30°) to avoid effects caused by differences in the local incidence angle. The fields include three different soil types to get more variation in SMC. In summary, it can be stated that at L-band, and especially at C-band, frequencies and an incidence angle of approximately 30°, the attenuation coefficient of the vegetation canopy is too high for monitoring soil moisture with only a monotemporal data set. Other parameters like phenology, plant density and geometry, and row direction mask differences in the SMC The results show that the backscattering, measuring using the P-band, can be well described with just two parameters. SMC is the dominant parameter influencing the backscattering. The secondary parameter is the row direction of the corn plants relative to look direction. With these two parameters, about 90% of the backscattering can be described. The best polarization combinations for SMC analysis are HH polarization and the difference in power between HH and HV polarizations. The study results suggest that the P-band is very suitable for soil moisture analysis from SAR imagery.