Intercomparisons between LSM and satellite-retrieved estimates of surface (0-5 cm) and root-zone (5-100 cm) soil moisture across the continental United States

Soil moisture plays a vital role in the partitioning of sensible and latent heat fluxes in the surface energy budget and the lack of a dense spatial and temporal network of ground-based observations provides a challenge to the initialization of the “true” soil moisture state in numerical weather prediction simulations. The retrieval of soil moisture using observations from both satellite-based thermal-infrared (TIR) and passive microwave (PM) sensors has been developed (Anderson et al., 2007; Hain et al., 2009; Jackson, 1993; Njoku et al., 2003). The ability of the TIR and microwave observations to diagnose soil moisture conditions within different layers of the soil profile provides an opportunity to use each in a synergistic data assimilation approach towards the goal of diagnosing the “true” soil moisture state from surface to root-zone.

The satellite retrievals of soil moisture will be compared to soil moisture estimates provided by a retrospective Land Information System simulation using the NOAH LSM during the time period of 2003 - 2008. The TIR-based soil moisture product is provided by a retrieval of soil moisture associated with surface flux estimates from the Atmosphere-Land-Exchange-Inversion (ALEXI) model (Anderson et al., 1997; Mecikalski et al., 1999; Hain et al., 2009). The PM soil moisture retrieval is provided by the Vrijie Universiteit Amsterdam(VUA)-NASA surface soil moisture product. The VUA retrieval is based on the findings of Owe et al. (2001; 2008) using the Land Surface Parameter model (LPRM), which uses one dual polarized channel (6.925 or 10.65 GHz) for a dual-retrieval of surface soil moisture and vegetation water content.

Each soil moisture product is scaled with respect to its climatology to provide a means to perform a direct comparison in the form of anomaly correlations during the 2003 - 2008 time periods. Comparisons between LSM and microwave-based soil moisture estimates are made with respect to the 0 - 5 cm soil layer of the NOAH LSM, while comparisons with TIR-based soil moisture estimates are made with respect to the root-zone (5 - 100 cm) soil layers.