|Hsu, Ann - ARS USDA HRSL|
|O Neill, P - NASA GSFC|
Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2002
Publication Date: December 1, 2002
Citation: Jackson, T., Hsu, A., O'Neill, P. 2002. Surface Soil Moisture Retrieval and Mapping Using High Frequency Microwave Satellite Observation in the Southern Great Plains. Journal of Hydrometeorology. 3:688-699. Interpretive Summary: The potential of passive microwave remote sensing for measuring surface soil moisture has been demonstrated over a range of microwave frequencies and a variety of platforms. These studies clearly show the advantages of low frequency (<5 GHz) microwave sensors for this application. Although low frequency sensors are recognized as the best direction for future soil moisture measurement systems, there is still a good reason in the meantime to consider the use of higher frequencies: the vast quantity of global systematic high frequency microwave data that have been collected for the past fourteen years by the Special Sensor Microwave/Imager (SSM/I). As part of the Southern Great Plains Hydrology Experiments conducted in 1997 (SGP97) and 1999 (SGP99), ground observations of soil moisture were made over an extended region in order to contribute to the validation and demonstration of large scale mapping of soil moisture using SSM/I data. Here a technique for extracting algorithm parameters from the observations was developed and tested. The algorithm was then used to produce soil moisture maps of the region for the two study periods. Subject to the assumptions made in its implementation, the algorithm worked well in these tests with SSM/I data. It is acknowledged that conditions in the SGP region are benign for the frequency used. However, it is anticipated that with lower frequency channels of soon to be launched satellite sensor systems the assumptions and limitations imposed by vegetation on soil moisture estimation will improve. These results will contribute to utilizing these long term satellite observations in understanding seasonal, annual, and decadal trends in soil moisture and its impact on agriculture, hydrology and climate.
Technical Abstract: Studies have shown the advantages of low frequency (<5 GHz) microwave sensors for soil moisture estimation. Higher frequencies have limited soil moisture retrieval capabilities, however, there is a vast quantity of systematic global high frequency microwave data that have been collected for fourteen years by the Special Sensor Microwave/Imager (SSM/I). SSM/I soil moisture studies have mostly utilized antecedent precipitation indice as validation, while only a few have employed limited ground observations, which were typically not optimal for this particular type of satellite data. In the Southern Great Plains (SGP) Hydrology Experiments conducted in 1997 and 1999, ground observations of soil moisture were made over an extended region for developing and validating large scale mapping techniques. Previous studies have indicated the limitations of both the higher frequency data and models for soil moisture retrieval. Given these limitations, an alternative retrieval technique that utilizes multipolarization observations was implemented and tested for the SGP region. A technique for extracting algorithm parameters from the observations was developed and tested. The algorithm was then used to produce soil moisture maps of the region for the two study periods.