2011 Annual Report 1a.Objectives (from AD-416) Proposal seeks to gain membership on the NASA SMAP mission science definition team. The science definition team will provide science feedback on SMAP mission design issues. 1b.Approach (from AD-416) We have proposed a series of data assimilation experiments to aid in SMAP algorithm development and inform SMAP mission trade-offs. 3.Progress Report Completed work on a peer-reviewed manuscript which evaluates the impact of transferring the source of land surface temperature data (required as input for surface soil moisture retrieval algorithms) from Ka-band microwave estimates to numerical weather model estimates. This transition is critical for the future NASA Soil Moisture Active/Passive (SMAP) mission since, unlike currently-available sensors, SMAP will lack a Ka-band channel and must therefore rely exclusively on numerical weather prediction models for required land surface temperature inputs. Results in the manuscript provide important context for understanding the expected role of land surface temperature errors on the quality of SMAP soil moisture retrieval products. In addition we contributed to the development of long-term (8-year) OSSE experiment over North America (using the SMAP algorithm test bed) to clarify the relationship between various soil moisture evaluation metrics and expected error sources in SMAP surface soil moisture retrievals.