Vegetation Effects at Frozen Environment by Simulation and Truck-mounted Microwave Radiometer

Passive microwave remote sensing techniques can be used to monitor freeze/thaw at frozen soil surface. Researches found that the negative spectral gradient at 19GHz and 37GHz was a good criteria for decision of frozen soil[1]. At vegetated area, to make the algorithm simple, vegetation scattering were ignored, only their attenuation were considered, which were kept constant, regardless of vegetation species, height etc. Many studies on microwave properties of vegetation showed that there exist big difference of scattering and attenuation of vegetation between different kinds of vegetation. The behaviors of lower grass are quite different from that of shrub or trees at 19GHz and 37GHz. Up to now to eliminate vegetation effect at frozen environment, the scattering and attenuation of vegetation are not exactly known. In this paper, a Matrix-Doubling (there after M-D)microwave emission model is used to evaluate vegetation effects at cold environment at Ku-band(18.7GHz) and Ka-band(36.5GHz). This model is based on ray tracing technique, of which multiple scattering inside vegetation layer and that between vegetation and surface could be considered. To verify the simulations of the M-D microwave emission model, a multi-channel truck-mounted radiometer, was employed to collect microwave emission data at a young forest stand at NE of CHINA during Jan. 2008, and a cole stubble area at Heihe River Basin during Chinese WATER (Watershed Airborne Telemetry Experimental Research) campaign on Mar. 2008, respectively. Comparisons between simulation results by M-D model and field experiments were good. Then we used the model to establish a database with a variety of parameters to simulate microwave emission of vegetated surface at frozen environment. Due to the complexity of M-D model, the results from the database were matched with that from a simple model ( model) at the same environment by least-square error, so as to retrieve scattering and attenuation of vegetation at Kuand Ka-band at cold environment.