Return to List of Research Summaries
TITLE:
Fusion of Optical and Synthetic Aperture Radar (SAR) Data to Estimate Plant and Soil Conditions
INVESTIGATORS:
Susan Moran, Jiaguo Qi, Wanmei Ni, Dan Hymer, and Michael Helfert (ARS)
OBJECTIVES:
1. To determine the sensitivity of ERS-2 SAR images to surface soil moisture conditions under differing vegetation types and covers.
2. To investigate the inter-changeability of Landsat TM spectral data with ERS-2 SAR spectral data for determination of soil moisture and vegetation cover.
APPROACH:
The general approach was to acquire pairs of ERS-2 SAR and Landsat TM scenes covering a similar area including the Upper San Pedro Basin and Walnut Gulch Experiment Watershed. These pairs would be acquired with less than one week between the two overpasses and would be scheduled to cover the entire growing season from mid-winter to late fall. During each acquisition set, we planned to make extensive measurements of soil and vegetation status (described in the next section). These measurements will be used in a SAR radiative transfer model to discriminate the SAR signal from the vegetation and soil components. Based on this data set, we will investigate the similarity between optical and SAR signal response to variations in soil moisture and vegetation density.
DATA COLLECTION:
Three sites were selected in large (300 x 300 m), relatively flat areas of uniform vegetation type. The dominant vegetation types at the three sites are creosote bush, sacaton grass and tobosa grass. At each site, a target was delimited of size 90x90 m, with flags set at grid spacing of 15 m. During each of ten planned ERS-2 overpasses, gravimetric soil moisture measurements at 5 cm depth are being made at the location of each flag (49 measurements total at each site). On a monthly basis, the vegetation cover, height, biomass, leaf area index and other characteristics are measured. We also have plans to characterize the site standard roughness and the soil bulk density. During the Landsat TM overpasses, we make a small sub-sample of soil moisture measurements to detect the change in soil moisture condition from the time of the SAR overpass. We also arrange for three measurements to allow atmospheric correction of the TM images: 1) surface reflectance and temperature over a large target, 2) radiosonde information based on a balloon launch from Ft. Huachuca, and 3) atmospheric optical depth based on measurements made with a multi-band solar radiometer.
DATA REQUIRED FROM OTHER INVESTIGATORS:
Though data is currently acquired in support of this work, some data would be interesting for comparison and for extension of this work to a larger area:
1. Any surface soil moisture information.
2. Any vegetation density or LAI information.
3. Any surface flux data.
4. Any measurements of surface reflectance and temperature.
5. ET data from the cottonwood/willow measurements.
6. LIDAR results.
7. Meteorological information on air temperature, wind speed and vapor pressure.
Return to List of Research Summaries
homepage