Soil moisture is a key player in global climate, agricultural yields, fire danger, and engineering analyses, yet is particularly difficult to measure over broad areas. Over the past few years I have led a team investigating the use of differential SAR interferometry (DInSAR) for the measurement of soil moisture. We now believe that DInSAR has more potential than any other technique currently being developed for this purpose.

This image shows what we believe is drying (blue) and moistening (yellow/red) between two SAR acquisitions in an arid region of Colorado. Black lines are stream channels. Note that ridges (where stream branches start) often show differences in color, which we believe likely indicates a difference in soil moisture due to different soil properties in this mesa topography. Pixel size is 50 m and image width is several kilometers.

The basic idea behind our technique is fairly simple. Because soil moisture affects the dielectric properties of the soil, it must also affect the penetration depth of microwaves into the soil. We believe that these changes in penetration depth are measurable with DInSAR as a path length change. Because these changes are small (on the order of millimeters), a high resolution DEM or appropriately small baseline offset must be used to detect them.

My colleagues and I have published several papers on this research. Note that the last paper is just a late draft and that the final version may differ slightly (due out in December 2003). Some background on why DEMs are important can be found here (EOS). Some background on why DInSAR should be a viable tool for measuring soil moisture can be found here (IEEE TGRS). Some results of using this technique at a site in southern Colorado can be found here (IEEE TGRS, in press). An 2001 AGU poster (converted to html) found here provides a general overview of the project and the results, as well as some 3D visualizations of the study area.

My current work involves using archived ERS scenes at a watershed in Alaska, SIR-C data from several world-wide locations, and experimental methods in the backyard.