Polarimetric backscattering measurements of herbaceous vegetation: a sensitivity study for soil moisture retrieval

In this paper, the feasibility of soil moisture retrieval from radar backscatter data acquired from surfaces covered with short, dense, and herbaceous vegetation such as soybean is studied. For this purpose, a series of polarimetric measurements were performed on a soybean field at L-, C-, and X-band frequencies over a wide range of incidence angles. In these experiments the University of Michigan polarimetric scatterometer systems were used. The backscatter measurements were conducted for two extreme vegetation conditions: (1) in the middle of the season for a fully grown soybean condition when vegetation biomass is maximum, and (2) toward the end of the season when the leaves were fallen and the plants were drier. For each vegetation condition backscatter measurements were also conducted under different soil moisture conditions to examine the sensitivity of radar backscatter to soil moisture. Simultaneous with the radar measurements, a complete set of ground truth data, including the moisture content, size and number density of leaves, stems, and pods were also collected. The dielectric constant of leaves and stems were also measured at C- and X-band immediately after radar measurements.