Abstract
Soil moisture is an important water cycle variable. The Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) program was the first to implement a soil moisture algorithm development and validation program that would lead to global standard products. A key aspect of the program was the inclusion of multiple research algorithms with continuing evaluation. One approach is the single channel algorithm (SCA) that utilizes the AMSR-E channel with maximum sensitivity in combination with ancillary data on vegetation conditions. Over the course of the AMSR-E project, this approach has been developed and improved. A critical component of providing a standard soil moisture product is its validation. As part of the AMSR-E validation program networks of dedicated validation sites were developed. These networks provide estimates of the average soil moisture over watersheds and surrounding areas that approximate the size of the AMSR-E footprint. Measurements have been made on a continuous basis since 2002. The NASA and JAXA standard soil moisture products were compared to the network observations, along with SCA. The results indicate that each algorithm has different performance statistics that depend upon the site and that there is much room for improvement in the algorithms adopted by JAXA and NASA. They also illustrate the potential pitfalls in using the products without caution.
