Passive Microwave Remote Sensing On Sand Desert Area--Taklimgan Sand Desert As A Case Study

As for passive microwave remote sensing, there are at least three aspects of meaning to study on sand desert area: 1) area in sand desert take a great percentage of the whole land area on earth, there is almost no vegetation in this area, so it can be used as natural calibration site for spaceborne microwave radiometer; 2) passive microwave remote sensing on sand desert is not only related to radiation of atmosphere and land surface, but also microwave penetration effects, essentially it is a problem of near-surface remote sensing. Thus it can be used as natural validation site for varies kind of emission model; 3) it can make more space for remote sensing applications. In addition, sand storm, wind storm that occurs in this area are also hot spots for passive microwave remote sensing.Passive microwave remote sensing on sand desert had seldom been studied so far. In this thesis, using Takelimgan Sand Desert as an example and spaceborne radiometry data as data source, passive microwave remote sensing on sand desert has been studied systemically. It includes spatial and temporal distribution of microwave radiometry characteristics, retrieving surface parameters, distribution of surface parameters and near-surface passive microwave remote sensing on sand desert area.Research before has illustrated that synergism of active and passive microwave remote sensing can be helpful to choose observing parameters to retrieve surface parameters, to improve accuracy of retrieving algorithm and deepen understanding of interactions between land surface and microwave radiation. But it has not been paidattention enough so far. And relationship between active and passive microwave remote sensing has been studied in detail using uniform based microwave scattering and emission model.Here below are the main works and conclusions in this thesis:1) Several microwave scattering models on random roughness surface have been described in detail, these models include geometric optical model, physical optical model, small perturbation model and integrated equation model. By comparison of these models with real observation data, every model can fit for real data in there validity conditions. IEM model can be applied for a wider range.By simulating the natural conditions and building up a database of backscattering coefficient and emissivities using IEM model, it is found that when ratio of rms height and correlation length is in some certain range, the ratio of backscattering coefficient to reflectivity is linear or polynomial with surface roughness. This relationship is independent of soil moisture. Backscattering coefficient can be calculated from emissivity using relationship derived in thi's thesis, and thus surface parameters can be retrieved by using empirical or semi-empirical emission models. This put forward a new method to retrieve surface parameters.2) By study on spatial and temporal distribution of Takelimgan Sand Desert using SMMR data, it is found that in most of time, brightness temperature in inner part of the desert is lower than around the desert. Map of brightness temperature illustrate a stable ring-like structure, brightness temperature in northeast corner is above that in southwest corner obviously. This can be affected by microwave sampling depth. In most time of a year, brightness on Takelimgan Sand Desert of V polarization of every frequency of SMMR is relatively uniform; the standard deviation is below 2K. Brightness temperature of H polarization is not as concentrated as V polarization, the standard deviation is below or about 2K. In summer, brightness temperature is more dispersed with influence of precipitation and clouds, the standard deviation of V polarization can reach 10K, and 16K for H polarization.For temporal distribution, it is symmetry between brightness temperatures of fore-half year and back-half year. Deviation among brightness temperatures of V polarization of SMMR frequencies are small, but brightness temperatures of high frequencies are higher and higher than that of low frequencies fro...