Using SMOS to study the Mississippi River basin water budget

The European Space Agency launched the Soil Moisture Ocean Salinity Satellite (SMOS) in November of 2009. The satellite retrieves surface (top few cm) soil moisture, and we evaluate the level 2 (L2) data stream. We compared SMOS L2 soil moisture retrievals to land surface observations at 5 cm depth coincident within one hour in the central United States for the period July 2010 to the present. The primary source of the surface data is the Soil Climate Analysis Network (SCAN), but we also used observations from the ARM/CART region in Kansas and Oklahoma, and from the United States Climate Reference Network (USCRN). While SMOS has a low bias in many locations, the temporal variations and spatial distribution are similar to the observations. SMOS, with a footprint of about 40 km, returns data along the borders of lakes and rivers, but may become contaminated and yield higher soil moisture values than those of the in situ data if the water bodies are within the footprint. We examine different areas of the Mississippi River basin to see which are most susceptible to this bias. These comparisons will be very useful for improving retrieval algorithms to allow SMOS to produce validated global surface soil moisture observations. This work is a step toward monitoring the entire Mississippi River basin water budget, an important goal of the lifetime work of John Roads.