Watershed Scale Surface Soil Moisture Variability in the Walnut Gulch Experimental Watershed During the 2004 North American Monsoon

In an effort to validate soil moisture satellite products, such as the Advance Microwave Scanning Radiometer (AMSR), diverse landscapes have been studied with intensive field campaigns. Semi-arid landscapes present a particular challenge to satellite remote sensing validation using traditional techniques because of the high spatial variability and potentially rapid rates of temporal change in moisture conditions. For one semi-arid watershed, temporal stability and other common techniques of geostatistical estimation are investigated for the watershed during a portion of the North American Monsoon season of 2004. The Walnut Gulch Experimental Watershed has a dense network of 88 precipitation gages of which 19 are collocated with soil moisture sensors providing an excellent location for satellite validation experiments. In conjunction with this monitoring network, intensive soil moisture field sampling, as part of the Soil Moisture Experiment in 2004 (SMEX04), contributed to the calibration of the network for large-scale estimation and added samples at additional raingages that did not have permanent sensors. Large-scale estimates can be calculated using a limited number of surface sensors with some qualifications. Geophysical aspects of the watershed, including topography and soil type are also examined for their influence on the soil moisture variability.