Soil Moisture Inversion Model Research Of Multi-Band And Multi-Polarization SAR Based On IEM

Soil moisture content plays a critical role in the surface energy balance at the soil-atmosphere interface and can be considered as a key state variable that influences the distribution of the radiant energy, the runoff generation and the percolation of water into the soil. Soil moisture monitor is always a focus in hydrology, meteorology and agriculture researches. In the past several decades, large scale soil moisture monitor by remote sensing, such as optical, infrared, and microwave methods have developed rapidly. Common methods and optical remote sensing have their own shortcoming in soil water monitor, thus cannot reach the need of soil water monitor. Active microwave techniques, particularly Synthetic Aperture Radar (SAR), take advantage of their all-weather and night-and-day measurement capacities, so it offers a new way to monitor soil moisture in drainage scale.Multi-polarization and multi-incidence angle is the tendency of space-borne SAR, so it is possible to reveal the relationship between radar backscatter coefficient and surface parameters by using different backscatter coefficient under different polarization mode and incidence angle. First three classical surface microwave backscatter model, i.e. Oh model, Dubois model and IEM model were compared and the IEM model was chosen in the following research. Empirical inversion model of surface roughness and soil moisture content were proposed on the simulation and analysis of surface backscatter characteristic under different input parameters (different bands and different polarizations) by using the IEM model.The results and innovations of this dissertation are mainly in the following aspects:(1) The comparison of Dubois model, Oh model and IEM model indicates that the Dubois model cannot describe the real backscatter character of surface under different dielectric constant or incidence angle, so it was not preferred in soil moisture inversion. Oh model can be used in cross polarization backscatter simulation. IEM model is preferred in co-polarization simulation because it can describe the backscatter character perfect.(2) On the basis of analysis of backscatter character under different surface roughness, soil water content, incidence angle and polarization conditions, the response of radar backscatter coefficient to these parameters was revealed.(3) An empirical model to inverse mixed surface roughness Z_s was proposed by using the backscatter coefficient difference between little and large incidence angles; then the empirical soil moisture inversion model was proposed based on the mixed surface roughness inversion model.(4) An empirical model to inverse RMS height was proposed by using the difference between VV and HH polarization backscatter coefficients under the same incidence angle. This model can inverse RMS height in a large roughness ranges. The use of the new empirical model can avoid tedious ground measurements to a great extent, and makes it possible to represent soil surface in pixel scale.(5) The backscatter characteristic at S band was simulated and analyzed for the first time, and the empirical modes for surface roughness and soil moisture were proposed. This research work provides technical support for the applications of S band space borne SAR of our country in the near future. (6) The surface roughness and soil moisture inversion models were applied in south Hebei Plain by using the ENVISAT-ASAR data and in situ experimental data. The inversion results of both parameters fitted the in situ data well.