Temporal stability of soil moisture profile

The temporal stability of soil moisture profile across the 610 km2 Little Washita River Experimental Watershed (LWREW), located in southwestern Oklahoma, is investigated. Experimental data were acquired by time-domain reflectometry (TDR) probes. TDR data were routinely collected at eight locations during the months of June and July in 1997 and in July 2003, coincident with large-scale hydrological remote sensing experiments. Analyses were performed to determine if a subset of the TDR sites could be used to represent watershed averages (i.e. sensor network averages) of soil water content at various levels in the soil profile, as well as in the total profile. The results show that two of the eight TDR sites were temporally stable. One site consistently underestimated and the other consistently overestimated watershed average soil water content at all levels in the soil profile. Because the offset between these under- and over-estimates and the watershed mean are known, these sites can be used to determine the watershed mean values of soil water content at all levels in the profile, as well as to provide ranges of soil water content within the watershed. Identification of these temporally stable sites within the LWERW will assist in the validation of coarse spatial resolution surface soil moisture products derived from remote sensing experiments, as well as providing data sets for watershed hydrologic modeling of subsurface soil water contents.