Overview

The Electronically Scanned Thinned Array Radiometer (ESTAR) has been used to retrieve soil moisture during field campaigns since 1992 (refer to estar11.shtml for more sensor information). This airborne L-band passive microwave remote sensing investigation is aimed to support algorithm development.

This dataset provides retrieved soil moisture based on the ESTAR observed L-band Microwave brightness temperature collected during the SGP99 experiment (July 10-20, 1999). At the beginning of SGP99, the experimental region was generally dry except for the northern portion of the area. On July 10th, a large, warm season rain event occurred over the northern two-thirds of the region. The rainfall totals at Oklahoma Mesonet stations at El Reno, Little Washita, and Central Facility were 107mm, 49mm and 37mm respectively. No other rainfall events occurred during the experiment, which resulted in a strong dry-down from the 10th through the 20th of July. This had made it a good case to validate soil moisture products derived from ESTAR at large dynamic range.

The science

This investigation applies a new soil moisture retrieval approach that utilizes a Land Surface Microwave Emission Model (LSMEM) for the soil-vegetation-atmospheric system with surface temperature data from a SVAT model that utilizes high resolution remotely sensed vegetation and soil data (Gao et al., 2003).

In the reviewed literature, a number of models for the computation of microwave emission from land surfaces exist. Depending on the specific application and frequency range they represent more or less complex approximations of the vector radiative transfer equation and distinguish themselves through different parameterizations for the key processes describing the interaction between radiation and matter. The LSMEM model used in this study is based on a solution for the radiative transfer equation as outlined in Kerr and Njoku (1990). More details about the LSMEM model as well as its comparisons with other emission models are available in Gao et al. (2003).

Besides the horizontal polarized brightness temperature from ESTAR, the LSMEM inputs include effective soil temperature, vegetation temperature, soil texture, surface roughness, soil bulk density, vegetation water content, and a vegetation structure parameter. By inverting the LSMEM with measured brightness temperatures, specified vegetation and soil properties, and computed atmospheric contributions, soil moisture is retrieved through a simple iterative procedure.

The retrieved soil moisture had the following RMS statistics when compared to field measurements during SGP99:

The files and data format

All files are contained in four subdirectories of the path and are described in the table below. For brightness temperature, soil moisture, and soil temperature MMDD refers to the month and day of the observations.

All data are 4 bytes binary images in big endian, consisting of 301 pixels wide by 801 lines with no headers. Following shows the Format and Georeferencing for all the files.

Data access and contact

FTP Site

The ESTAR Retrieved Soil Moisture data files from SGP99 reside on DAAC anonymous FTP. You may access them from this document

ESTAR Data (ASCII) Data Online

or directly via ftp at

ftp disc.gsfc.nasa.gov

login: anonymous

password: < your internet address >

cd http://disc.sci.gsfc.nasa.gov/data/sgp99/air_remote_sensing/estar

Points of Contact

Acknowledgment of the dataset

Use of the dataset should contain the following acknowledgement: "The SGP99 soil moisture data set was provided by Princeton University, and is described in Gao et al. 2003. Using a Microwave Emission Model to Estimate Soil Moisture from ESTAR Observations During SGP99, J. Hydrometeorology (in press)."

References

Kerr, Y.H. and E.G. Njoku, A semiempirical model for interpreting microwave emission from semiarid land surfaces as seen from space, IEEE Trans. Geosc. Rem. Sens. 28, 384-393, 1990.

Gao, H., E. F. Wood, M. Drusch, W. Crow, T. J. Jackson, Using a Microwave Emission Model to Estimate Soil Moisture from ESTAR Observations During SGP99, submitted to J. Hydrometeorology