Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2006
Publication Date: 2/15/2008
Citation: Cosh, M.H., Jackson, T.J., Moran, M.S., Bindlish, R. 2008. Temporal persistence and stability of surface soil moisture in a semi-arid watershed. Remote Sensing of Environment. 112:304-313. Interpretive Summary: Satellite remote sensing of the land surface requires some ground-based validation to insure the satellite is accurate. The diversity of the land surface requires robust and flexible algorithms as well as good quality ground information to produce a valuable satellite program. The Advanced Microwave Scanning Radiometer (AMSR-E) is one such satellite instrument, which produces a soil moisture product for the earth’s land surface. Land validation data for soil moisture can be collected several ways, but the most cost efficient is in situ networks at large scales. This study investigates the quality of one such network in southeastern Arizona, known as the Walnut Gulch Experimental Watershed. This network is found to have a very good agreement with the average watershed soil moisture as determined by high density sampling that was conducted as part of a large scale experiment. Also, the network is shown to be temporal stable, indicating it is consistent and reliable over time. Finally, a comparison of a satellite measure (emissivity) to the watershed average indicates that future calibration and validation efforts using this watershed should be fruitful.
Technical Abstract: Satellite soil moisture products, such as the Advanced Microwave Scanning Radiometer (AMSR), require diverse landscapes for validation. 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 statistical techniques are used to investigate different methods of quantifying satellite scale soil moisture in a semi-arid region. The Walnut Gulch Experimental Watershed has a dense network of 19 soil moisture sensors providing an excellent location for satellite validation experiments. In conjunction with this monitoring network, intensive gravimetric soil moisture sampling, as part of the Soil Moisture Experiment in 2004 (SMEX04), contributed to the calibration of the network for large-scale estimation. The sensor network is shown to be an excellent estimator of the watershed average; however, the soil moisture pattern is not replicated by the network. Geophysical aspects of the watershed, including topography and soil type are also examined for their influence on the soil moisture variability. Soil type, as characterized by clay and sand content, was responsible for nearly 60% of the temporal stability. Topographic effects were less important in defining representativeness and stability.