|Keefer, Timothy - Tim|
Submitted to: First Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: 8/20/2002
Publication Date: 9/15/2003
Citation: Kennedy, J.R., Keefer, T.O., Paige, G.B., Barnes, E. 2003. Evaluation of dielectric constant-based soil moisture sensors in a semiarid rangeland. Proceedings First Interagency Conference on Research in the Watersheds. Oct. 27-30, 2003. Benson, AZ., pp.503-508. Interpretive Summary: Soil moisture can be an important factor for land managers to consider when making decisions concerning livestock grazing patterns, crop planting and irrigation scheduling, and soil stability for machinery traffic. In this paper, the authors discuss the use of soil moisture probes, designed to be buried and left in place, to collect data in order to improve the accuracy of satellite images of soil moisture. The paper presents results showing the accuracy of the probes, the proper sampling interval at which to sample the probes, and trends in the movement of water through the soil profile. The findings will be useful to scientists using satellite images to determine soil moisture, as well as scientists and land managers who would like to install soil moisture probes for data collection at other sites in semiarid rangelands.
Technical Abstract: In winter 2002, nineteen Stevens Vitel Hydra soil moisture probes were installed at the USDA-ARS Walnut Gulch Experimental Watershed to provide surface soil moisture data for use in calibrating remote sensing instruments. At three sites, two additional probes were installed at depth to provide a profile of soil moisture. The probes accurately measure soil moisture after applying a linear regression to match Vitel volumetric water content with gravimetrically sampled VWC. Probes at 5 cm and 15 cm responded quickly to larger rainfall events, while the one at 30 cm showed a delayed and gradual response. The optimal sampling interval was about 5 minutes during a rainfall event at 5 cm and 15 cm and no less than 30 minutes at 30 cm depth. During dry periods, the probes may be sampled at longer intervals, 30 minutes or greater, with no loss in data quality. Soil water was redistributed from the surface to 30 cm depth during the summer rainy season and to 15 cm depth during the winter rainy season.