Key Technology Of Terrain Radiation Correction In Spaceborne SAR Remote Sensing Inversion

SAR data is widely used in many fields, such as Agriculture. forestry resources survey in mountain area, and Mountain ecological monitoring. Due to the rise and fall of the landscape, when the montain areas are rugged, the echo received from each image element on the ground of the corresponding SAR images display huge differences. Therefore, the radiation values is different in each gradient and slope for the same type of the surface coverage type. Even the image was echo from the same objects on the ground may with different Brightness values. The orographic effect had became the main obstacle of the further use of the SAR data. Comparing with optical image, the orographic effect of the SAR image is quite obviously which we called it Terrain radiometric correction. As in our country there are almost 70% montain areas, the reserch on the terrain radiometric corredtion of the SAR image is not only the hot issue in the area of remote sensing science theory,but also a meaningful applied technology in fields such as forestry survey, resources environment and ecology.With the purpose of setting southwest plateau area as an example, this study select the research area in xianggelila and studies the influence of terrain in SAR images, then we discusses their image mechanism and corresponding methods. With these studying we expected to impove the posibilitiy and precision of the use of remote sensing inversion in the terrain riases and falls areas.The results of this study are achieved in the following six areas:1.This paper analyzes the geometry conformation of spaceborne SAR, the parameters and characteristics of the ground parameters which affecting the SAR image of the SAR system. Moreove, it analyzes the orographic effect of SAR image and draws the conclusions that there are two main factors about orographic effect: one is the effective area and another is the incident angle.2. Through the establishment of SAR locating model, this paper analyzs the metadata of DEM and SAR data, builds the coordinates table of DEM and SAR data, and with the simulated SAR image we obtained the orthorectifies image of SAR data using the forward and backward coding methods. 3. According to imaging mechanism of the Spaceborn SAR, the changes of the effective scattering area causing by terrain variation is analyzed and its area is adjusted at the same time. With the analysis of theory this paper developed three correction methods in the field of correction of effective area. With the comparing of the effect of three methods in the study area, we compared the relationship between backscattering coefficients and incident angle before and after correction. At the same time we compared the the difference histogram of different calibration results. In order to verify the effectiveness of the correction of remote sensing inversion, we discussed the correlation between the biomass of Pinus densata Mast and backscattering coefficients. With these analysis we get the effective method to the study aera.4. In this paper, we analysis the effect of incident angle to the different backscattering cofficients, with the basis of it we selected forest as the research object and we set the improved water-clouds model based on the water-clouds model and the first order transmission model. the effectiveness of the special model is confirmed by making comparison of model estimation and the measured backscatter data,. The results of the research indicates that the the error of the simulative scattering coefficient of the C-hand of HH is no more than 2dB while that of HV is less than 1Db.5. Basing on the constructed model, this paper analysis the effects which have being caused by incident angle on the scattering mechanism of the microwave of the forest. With the assuming that the tree trunk growing vertically and the backscattering coefficients is mainly affected by the conopy, we constructs the semiempirical-checking model of incident angle, in order to improve the precision of value of n in the model. This paper put forward that using the linear model to predict, as a example, we used HV data and treating yunnan pine as the research object and builds checking model of the incident angle of yunnan pine varying different age.6. The purpost of terrain correction is mainly used to inversion of vegetation parameters, in this paper, we evaluates the effectiveness of the model with the inversion of yunnan pine. With the result we can see that the correlation of backscattering coefficients after terrain radiation and biomass of Yunnan pine improves significantly, and at the same time the precision of inversion of the model and variance parameters had improved.