The Science Investigator-led Processing System (SIPS) has released the AMSR-E/AMSR2 Unified L2B Half-Orbit 25 km EASE-Grid Surface Soil Moisture data set. This data set provides a long-term data record (23 July 2002 through present) using a combination of AMSR-E and AMSR2 data with reprocessed AMSR-E L1R brightness temperatures. Backprocessing is ongoing, with data available from 23 July 2012 to date.
These data are available at the NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC).
Data set DOI: http://dx.doi.org/10.5067/IKQ0G7ODMLC7