Submitted to: Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: 5/9/2003
Publication Date: 10/27/2003
Citation: Cosh, M.H., Jackson, T.J., Bindlish, R., Prueger, J.H. 2003. Estimation of watershed scale soil moisture from point measurements during SMEX02. Interagency Conference on Research in the Watersheds. p.205-211. Interpretive Summary: Estimating soil moisture on the scale of 10km is a difficult task for hydrologists. However, the proliferation of in situ measuring sites now enables estimates to be made over a large area with limited resources. There is a need to understand how the siting of these in-situ sites can affect those estimates. Temporal and spatial stability analysis are employed to study a watershed scale soil moisture monitoring network in Central Iowa as part of the SMEX02 experiment. This study shows that with simple techniques a stable set of locations within a watershed can be identified as estimating the large scale moisture average with low bias and error. The results of this study will improve the ability of hydrologists to calibrate and validate satellite soil moisture products which have been recently deployed.
Technical Abstract: Watershed scale soil moisture estimates are necessary to validate current remote sensing products, such as those from the Advanced Microwave Scanning Radiometer (AMSR). Unfortunately, remote sensing technology does not currently resolve the land surface at a scale that is easily observed with ground measurements. One approach to validation is to use existing soil moisture measurement networks and scale these point observations up to the resolution of remote sensing footprints. As part of the Soil Moisture Experiment 2002 (SMEX02), one such soil moisture gaging system, in the Walnut Creek Watershed, Iowa, provided robust estimates of the soil moisture average for the watershed. Twelve in-situ soil moisture probes were installed across the watershed. These probes recorded soil moisture at a depth of 5 cm from June 29th, 2002 to August 19th, 2002. The sampling sites were analyzed for temporal and spatial stability by several measures including mean relative difference and Spearman rank. Representative point measurements were scaled up to the watershed scale (~25 km) and shown to be accurate indicators with low variance and bias of the watershed scale soil moisture distribution. This work establishes the validity of this approach to provide watershed scale soil moisture estimates in this study region for the purposes of satellite validation. Also, the potential errors in this type of analysis are explored. This analysis is an important step in the implementation of large-scale soil moisture validation using existing networks such as the Soil Climate Analysis Network (SCAN) and several Agricultural Research Service watersheds as a basis for calibrating satellite soil moisture products.