USING REMOTE SENSING & MODELING FOR EVALUATING HYDROLOGIC FLUXES, STATES, & CONSTITUENT TRANSPORT PROCESSES WITHIN AGRICULTURAL LANDSCAPES
Title: Validation of Advanced Microwave Scanning Radiometer Soil Moisture Products
Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 9, 2010
Publication Date: December 1, 2010
Citation: Jackson, T.J., Cosh, M.H., Bindlish, R., Starks, P.J., Bosch, D.D., Seyfried, M.S., Goodrich, D.C., Moran, M.S. 2010. Validation of advanced microwave scanning radiometer soil moisture products. IEEE Transactions on Geoscience and Remote Sensing. 48:4256-4272.
Interpretive Summary: Global soil moisture products are now being operationally generated by space agencies in the U.S. and Japan. Validating these products is critical to the potential users who must know whether they are accurate and reliable. The disparity of spatial scales between what we have available on the ground to the large domains that the satellite observes makes this a challenging task. In this study, soil moisture products were compared to in situ observations derived from networks developed specifically for this purpose. The results indicate that each of the products evaluated had different performance statistics that depend upon the site and that there is much room for improvement. A positive outcome of the analysis is that it appears that the approaches do perform within reasonable error bounds. Soil moisture products from satellite sensors have the potential to dramatically improve the accuracy and timeliness of weather, climate, and agricultural assessments and forecasts used by USDA, NOAA, and other agencies.
Validation is an important and particularly challenging task for remote sensing of soil moisture. The key issue in the validation of soil moisture products is the disparity in spatial scales between satellite and in situ observations. Conventional measurements of soil moisture are made at a point whereas satellite sensors provide an integrated area/volume value for a much larger spatial extent. In this investigation, four soil moisture networks were developed and used as part of the Advance Microwave Scanning Radiometer-Earth Observing System (AMSR-E) validation program. Each network is located in a different climatic region of the U.S., and each provides estimates of the average soil moisture over highly instrumented experimental watersheds and surrounding areas that approximate the size of the AMSR-E footprint. Soil moisture measurements have been made at these validation sites on a continuous basis since 2002 that provided a seven year period of record. The NASA and JAXA standard soil moisture products were compared to the network observations; along with two alternative soil moisture products developed using the single channel algorithm (SCA) and land parameter retrieval model (LPRM). The statistical results indicate that each algorithm performs differently with respect to each site. Neither the NASA nor JAXA standard products provide reliable estimates for all the conditions represented by the four watershed sites. The JAXA algorithm performs better than the NASA algorithm under light vegetation conditions and the NASA algorithm is more reliable for moderate vegetation. However, both algorithms have a moderate to large bias in all cases. The SCA performed better overall with a small bias. The performance of the LPRM was poor with a very large overestimation bias and retrieval errors that appear to be linked with seasonal variables. These results clearly show that there is much room for improvement in the algorithms currently in use by JAXA and NASA. They also illustrate the potential pitfalls in using the products without a careful evaluation.