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Title: Aircraft based soil moisture retrievals under mixed vegetation and topographic conditions

item Jackson, Thomas
item KLEIN, M
item Cosh, Michael
item WATTS, C
item VIVONI, E
item Bolten, John
item Keefer, Timothy

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2007
Publication Date: 2/15/2008
Citation: Bindlish, R., Jackson, T.J., Gasiewski, A., Stankov, B., Klein, M., Cosh, M.H., Mladenova, I., Watts, c., Vivoni, e., Lakshmi, v., Bolten, J., Keefer, T. 2008. Aircraft based soil moisture retrievals under mixed vegetation and topographic conditions. Remote Sensing of Environment. 112:375-390.

Interpretive Summary: The effects of land surface variations and rugged topography on passive microwave remote sensing of soil moisture were quantified using aircraft and satellite based instruments. Significant results included the consistency in response at aircraft and satellite spatial resolution, which supported linear scaling of soil moisture and brightness temperature even with the heterogeneous land conditions. This consistency also supports the conclusion that both instruments are adequately calibrated for land studies. These results show that it is possibility possible to retrieve soil moisture in areas of moderate vegetation biomass and high topographic variability at aircraft spatial resolutions. A more in-depth study that studies the sub-pixel behavior at finer resolutions maybe needed to fully understand the effect of topography. The PSR based soil moisture products will provide an excellent resource for the study of the effects of land surface (soil moisture in particular) on the North American Monsoon System. It is anticipated, that the results of this analysis will provide valuable input parameters for coupled land-atmosphere models used to investigate the importance of surface parameterization. The improved parameterization may lead to more accurate predictions of annual water supplies in the western U.S., which will impact agricultural management and productivity.

Technical Abstract: An unresolved issue in global soil moisture retrieval using passive microwave sensors is the spatial integration of heterogeneous landscape features to the nominal 50 km footprint observed by most satellite systems. One of the objectives of the Soil Moisture Experiments 2004 (SMEX04) was to address some aspects of this problem, specifically variability introduced by vegetation, topography and convective precipitation. Other goals included supporting the development of soil moisture data sets that would contribute to understanding the role of the land surface in the concurrent North American Monsoon System. SMEX04 was conducted over two regions: Arizona - semi-arid climate with sparse vegetation and moderate topography, and Sonora (Mexico) - moderate vegetation with strong topographic gradients. The Polarimetric Scanning Radiometer (PSR/CXI) was flown on a Naval Research Lab P- 3B aircraft as part of SMEX04 (10 dates of coverage over Arizona and 11 over Sonora). Radio Frequency Interference (RFI) was observed in both PSR and satellite based (AMSR-E) observations at 6.92 GHz over Arizona, but no detectable RFI was observed over the Sonora domain. The PSR estimated soil moisture was in agreement with the ground-based estimates of soil moisture over both domains. The estimated error over the Sonora domain (SEE=0.021 cm3/cm3) was higher than over the Arizona domain (SEE=0.014 cm3/cm3). These results show the possibility of estimating soil moisture in areas of moderate vegetation and high topographic variability.