Validation of AMSR-E soil moisture algorithms with ground based networks

Validation of satellite-based soil moisture algorithms and products is particularly challenging due to the disparity of scales of the two observation methods. Validation programs for the Advanced Microwave Scanning Radiometer-E (AMSR-E) instrument on the Aqua satellite is currently ongoing. As part of the AMSR-E validation activities several networks of ground based in-situ soil moisture sensors were established in research watersheds. These networks provide estimates of the average soil moisture over the watersheds and surrounding areas that approximate the size of the AMSR-E passive microwave footprint. Four watersheds in different vegetation/climate regions of the U.S. were selected. All instrumentation was installed prior to the launch of AMSR-E in 2002. There are now over five years of observations available. Quality control of the data has included short term field experiments at some of the watersheds to verify calibration and scaling. The National Aeronautics and Space Administration (NASA) and Japanese Aerospace Exploration Agency (JAXA) soil moisture products were compared to the network observations, along with an alternative algorithm. The results indicate that each algorithm has different performance statistics that depend upon the site. A positive outcome of the analysis is that it appears that the algorithms have the potential to perform within acceptable error bounds. Preliminary results indicate the single channel algorithm performs very well in all four watersheds. These results are not final because the products of both agencies are undergoing revisions. The issues addressed here are common to both current and future satellite missions.