TEMPORAL STABILITY OF PROFILE SOIL MOISTURE

Authors: Starks, Patrick; Heathman, Gary; Jackson, Thomas; Cosh, Michael

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2005
Publication Date: 6/1/2006
Citation: Starks, P.J., Heathman, G.C., Jackson, T.J., Cosh, M.H. 2006. Temporal stability of profile soil moisture. Journal of Hydrology. 324:400-411.

Interpretive Summary: Validation of satellite estimates of surface soil water content and verification of model simulations of sub-surface soil water content over large land areas cannot be accomplished in a timely, cost-effective manner using traditional manual sampling techniques. This study analyzes the consistency, both in space and time, of profile soil moisture content obtained from time-domain reflectometry (TDR) probes deployed across the 610 km2 Little Washita River Experimental Watershed (LWREW) located in southwestern Oklahoma. Analyses were performed to determine if a smaller number of the TDR sites could be used to represent watershed averages of soil water content at various levels in the soil profile, as well as in the total profile. TDR data were routinely collected during the months of June and July in 1997 and in July 2003, coincident with large-scale hydrological remote sensing experiments. The results show that two of the sites were stable, as evidenced by their small standard deviations. 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 consistent and 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 providing 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 new generation passive microwave satellites, as well as providing validation data sets for watershed hydrologic modeling of subsurface soil water contents.

Technical Abstract: Validation of satellite estimates of surface soil water content and verification of model simulations of sub-surface soil water content over large land areas cannot be accomplished in a timely, cost-effective manner using traditional manual sampling techniques. This study analyzes the temporal stability of profile soil moisture content obtained from time-domain reflectometry (TDR) probes deployed across the 610 km2 Little Washita River Experimental Watershed (LWREW) located in southwestern Oklahoma. Analyses were performed to determine if a subset of the TDR sites could be used to represent watershed averages of soil water content at various levels in the soil profile, as well as in the total profile. 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. The results show that two of the eight TDR sites were found to be temporally stable, as evidenced by their small standard deviations. 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 providing 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 new generation passive microwave satellites, as well as providing validation data sets for watershed hydrologic modeling of subsurface soil water contents.