USING TRMM/TMI TO RETRIEVE SOIL MOISTURE OVER THE SOUTHERN UNITED STATES FROM 1998 TO 2002:

Authors: GAO, H - PRINCETON UNIVERSITY; WOOD, E - PRINCETON UNIVERSITY; Jackson, Thomas; DRUSCH, M - EUROPEAN METEROLOGICAL; BINDLISH, R - SSAI

Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2005
Publication Date: 3/1/2006
Citation: Gao, H., Wood, E.F., Jackson, T.J., Drusch, M., Bindlish, R. 2006. Using TRMM/TMI to retrieve soil moisture over the southern United States from 1998 to 2002. Journal of Hydrometeorology. 7:23-38.

Interpretive Summary: Soil moisture across the southern United States were mapped over a 5-year period using measurements from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) X-band (10.7 GHz) radiometer with a land surface microwave emission retrieval model (LSMEM). Passive microwave remote sensing has been recognized as a potential source of soil moisture, and when combined with field observations and hydrological modeling can describe in real-time soil moisture information at large scales. Long term operational data sets have been lacking. Surface temperatures, needed for the retrieval algorithm because of the TMI single-frequency, single-polarization measurements, were obtained from the Variable Infiltration Capacity (VIC) hydrological model using North American Land Data Assimilation System (NLDAS) forcings. The resulting retrieved soil moisture are available to the community at a 1/8th degree spatial resolution for each TMI orbit, and as a daily average (of all orbits) across the southern U.S. for the 5-year period of January 1998 through December 2002. It is our expectation that this data set, with its accompanying data quality flags will provide a unique data set for the research community in addressing the above, and similar, science questions. Furthermore, this data set will assist in evaluating retrieved soil moisture from AMSR-E, which is on the NASA Aqua polar-orbiting platform, and was launched in early 2002. This is a positive step towards the development of more robust techniques based upon a data source that is globally available on a routine basis that will be of value agricultural managers and modeling.

Technical Abstract: Passive microwave remote sensing has been recognized as a potential source of soil moisture, and when combined with field observations and hydrological modeling can describe in real-time soil moisture information at large scales. However, operationally acquiring reliable soil moisture products from satellite observations has been hindered by three limitations: suitable low-frequency passive radiometric sensors that are sensitive to soil moisture and it change; retrieval models, and their parameters, that can provide estimates of soil moisture from top-of-atmosphere (TOA) microwave brightness temperature measurements; and suitable, large-scale validation data sets. In this paper, we retrieve soil moisture across the southern United States using measurements from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) X-band (10.7 GHz) radiometer with a land surface microwave emission retrieval model (LSMEM) developed by the authors. Surface temperatures, needed for the retrieval algorithm because of the TMI single-frequency, single-polarization measurements, were obtained from the Variable Infiltration Capacity (VIC) hydrological model using North American Land Data Assimilation System (NLDAS) forcings. Because of limitations in the retrieval algorithm for heavy vegetated areas, active precipitation, snow covered surfaces, and frozen ground, quality control flags for the retrieved soil moisture are provided. The resulting retrieved soil moisture are available to the community at a 1/8th degree spatial resolution for each TMI orbit, and as a daily average (of all orbits) across the southern U.S. for the 5-year period of January 1998 through December 2002.