Retrieval For Albedo Of Ground Surface And Thermal Effect Analysis On Tibetan Plateau

Albedo is one of the most important factor which effect the balance of the outing and incoming solar energy of ground surface. Because Tibetan Plateau has the highest elevation on the world and a vast area, its albedo performs a most important influence to the atmospheric motion and climate of the region, and even of the globe. The objective of this paper is to retrieve the albedo of the plateau and then to calculate the parameters about hot or cold source quantitatively. To gain a higher precision of retrieval, the method of pixel information decomposition is introduced in. The method is to divide ground objects correspond to a pixel in to several basic components: soil, vegetation, moisture, water, and ice, and then, using remote sensing data, calculate the contents of every components according to the model by which the component's spectrum compose. After that semi-globe direction reflectance and albedo of pixel are calculated according to the contents of every component.For that, the relationship between soil spectrum and water content and the roughness of soil surface are deeply studied in the paper. And the exponent relation between water content and soil spectrum are demonstrated, then the function of water content and soil spectrum are put forwarded, and the curve of absorption coefficient of water content in soil measured. Basing the study on the course of reflection and scattering taking place on soil surface, a function of relation between soil spectrum and the roughness of clod was put forwarded. Then a mathematic model on the relation between soil spectrum and water content and surface roughness are proposed. The model was verified by experiment.To the aspect of bi-directional reflection distribution function of vegetation, according to the characteristics of the vegetation over Tibetan Plateau, a new model was proposed by improve Hapke's model to consider the scattered flux of the first three times, which obviously promote the precision, but the amount of calculation is reduced.To the influence of the plateau terrain, the impact of the elevation and the roughness of terrain to every energy component out and incoming are study, and basing the soil spectrum model proposed above, a new radiative transfer model of terrain area was put forwarded in which the soil water content, LAI, terrain roughness and elevation were considered synchronously, and incoming scatter light was integral with the solid angle of semi-globe space defined by the slope of the pixel, soscattering lights of terrain and the sky are properly considered, but the operation is still within the acceptable range.Basing the radiative transfer model of terrain area, a new model for calculating the albedo over terrain area was put forwarded by improve Irons' model of albedo calculation with 10 spectrurns. Using this model, albedos over Tibetan Plateau of different time were calculated. The results of albedo have higher precision than that get by traditional method. The result images showed that the distribution of albedo has a close connection with terrain and snow. Rough terrain areas have lower albedo, when albedo on snow area is much higher than other area. By comparing the albedo image of winter and summer, it is shown that albedo of Tibetan Plateau in winter is obviously large than that of in summer. The cause is that there are large distribution areas of moistly soil, wetly lands, and vegetative land, and smaller area of snow on the plateau.Then basing the empirical formal proposed by Weng Burning, a method for reckon the average flux of energy transfer from ground surface to the air of a day according albedo and terrain parameters was put forwarded. It is considered that the flux is a proper index to decide if the area is a hot source or a cold source. The average flux of energy transfer from ground surface to the air of a day of Tibetan Plateau in summer, 1998; the Summer Solstice and midwinter, 2000 are calculated. The results show that the flux has a positive relationship with elevation, and that, Tibetan Platea...