Soil Moisture


Soil moisture is fundamental to land surface hydrology, so global distribution and temporal variations of soil moisture are needed both for analyses and modeling purposes. To date, a global soil moisture dataset that fulfills the needs of the hydrology and climate communities does not exist: in situ measurements are sparse and useful satellite-derived methods are still being developed. Recently, it has been shown that high-precision GPS receivers can be used to estimate fluctuations in near surface soil moisture over an area of ~1000 sq. meters. Given this sensitivity to soil moisture, some of the more than 1500 permanent and continuously operating GPS receivers that exist in the U.S. can be used to provide near-real time estimates of soil moisture for hydrology, climate, and ecology studies.

We are currently testing the GPS reflection technique for soil moisture at new sites to assess the impact of vegetation and soil type: Boulder County Open Space, Munson Farms, Marshall, the Sevilleta LTER, and the Oklahoma SMAP in situ testbed.

Daily precipitation (blue), water content reflectometer range (gray), and GPS soil moisture measurements (colors) for PBO GPS site at Marshall, CO.  Details given in Larson et al. [2008].