Microwave Emission and Plant Water Content: A Comparison between Field Measurements and Theory

Microwave radiation from a canopy cover depends primarily on the vegetation's thermal and dielectric properties; the latter are dependent on plant biometrical parameters and water content. Emission measurements carried out by means of ground-based X-and Ka-band radiometers have shown that crop coverage of soil can be detected through the spectral signatures of bare soil and vegetation. Moreover, measured brightness temperature and the radiative transfer theory for a scattering medium allow estimation of the scattering and absorption properties of the canopy. These parameters have been computed for corn and alfalfa using experimental data and a simple model in which anisotropic scattering is considered by means of transformed parameters w' and r'. We found that the single scattering albedo w' is always lower than 0.1, whereas the optical depth T' is very high. The latter has been correlated to plant water content by means of a logarithmic function.