Comparison of spatial statistics of SAR-derived and in-situ soil moisture estimates

The technology of using spaceborne SAR systems for soil moisture estimation has been refined over the last few years. In order to reduce the confounding effects of surface roughness on soil moisture inversion, multifrequency SAR systems have shown promise. The Shuttle Imaging Radar (SIR-C) has an onboard SAR system operating at L-, C-, and X-bands for high resolution imaging of the Earth´s surface. Over the early part of October 1994, the SIR-C SAR collected radar reflectance data from two sites near Concord, New Hampshire. SIR-C data were collected on four consecutive days and concurrent ground truth measurements were also made of the actual soil moisture distribution at the test sites. The objective of the study was to evaluate the radar system´s ability not only to estimate soil moisture, but also to characterize its spatial variability. The University of Nebraska has developed inversion algorithms to estimate soil moisture from SIR-C data. The spatial statistics of the in-situ measurements were used to refine the soil moisture inversion algorithm. The SIR-C derived and the in-situ soil moisture estimates compared well not only for the mean soil moisture of each pixel, but also for the spatial statistical parameters, such as correlation lengths and the gradients of soil moisture