On combined sampling of soil moisture using ground-borne and spaceborne sensors

Adequate knowledge of soil moisture storage as well as evaporation and transpiration at the land surface is essential to the understanding and prediction of the reciprocal influences between land surface processes and weather and climate. Traditional techniques for soil moisture measurements is ground-based, but space-borne sampling is becoming available due to recent improvement of remote sensing techniques. A fundamental question regarding the soil moisture observation is to estimate the sampling error for a given sampling scheme (North and Nakamoto, 1989; Kim et al., 1999). In this study we provide the formalism for estimating the sampling errors for the cases of using ground-borne sensors, space-borne sensors and both. For the study a model for soil moisture dynamics by Entekhabi and Rodriguez-Iturbe (1994) is introduced and an example application is given to the Little Washita basin using the Washita '92 soil moisture data. As a result of the study we found that the ground-borne sensor network is ineffective for large or continental scale observation, but should be limited to a small-scale intensive observation such as for a preliminary study.