| The variation of regional land surface Evapotranspiration (ET) reflects the trend of energy and water balance in land surface process. Also it further affects distribution of the regional climate and water, and thus has an impact on regional economic development. With the development of remote sensing technology, it becomes more easily to explore the land surface ET of large scale. Therefore, it is a promising theme to carry out a research related to monitoring land surface energy and water balance on regional scale based on the remote sensing technique.Based on the remote sensing technique, using ETM+and MODIS, two different scales of remote sensing data, and also bringing DEM data, the thesis improves the generally-applied SEBS model and expands its application in the situation where the topography is complicated. At the same time, it explores how these two different data with different scales affect the accuracy of ET. It also builds a multi-scales remote sensing model by using data of ETM+and MODIS to improve the scale effect (mixed pixel) of the MODIS data. The thesis regards the YILUO River basin as a case, and also analyses and explores the temporal and spatial distribution of land surface ET in the year2002and2008, which has more important theoretical and practical value. Specific research work and conclusions of this paper are as follows.1) ETM+and MODIS can be used to estimate the regional land surface ET better. Especially, the estimate result which uses the ETM+data is more accurate than that uses the MODIS data. Comparison with ground truth data shows that the average relative error is of10%and20%and high-resolution image data can improve ET estimation accuracy to some extent.2) DEM-based net radiation flux estimation mountain area mode can be used in the net radiation flux estimation of complex terrain area.Taking into account of the regional sea level elevation, ratio of slope, aspect and the shelter of the topography around in a mountain area model, it corrects the topography affected by the sun radiation from three aspects:firstly. according to the factors such as ratio of slope, aspect, latitude to correct the cosine of slope angle of the sun; Secondly, using the cosine ratio of the slope angle of the sun and solar zenith angle to correct the radiation quantity the slope received; Finally, it introduces a binary function-terrain masking factor to correct the impact of near terrain shadowing. The empirical results in the experimental area show that the net radiation flux estimation result without the consideration of DEM can not reflect the feature of the land surface, so we must take the effect of the topography into consideration.(3) The improved SEBS model of ET is of higher accuracy, and has a better adaptability and stability in the studied area.Based on the widely-applied SEBS model and introducing DEM data, it carries out the terrain (elevation, slope, aspect) amendments on the surface parameters and Kinetic parameters such as the solar radiation, atmospheric transmittance, land surface temperatures and land surface roughness, which makes the SEBS model can even adapt to complicated geography condition, and expands the application of the regional surface ET model. The application result of the studied area indicates that the daily ET amount estimated by the improved SEBS model has a smaller error with the measured value, and a higher accuracy. The suitability and stability of the model is better. Making use of ETM+data, the surface ET estimation in the studied area is more accurate than a MODIS data. The SEBS model can better reflect the land cover type and pattern of spatial and temporal distribution of water in the studied area.(4) This paper analyzes the size error caused by the mixed pixel in ET estimation with MODIS data. It sets up the multi-scale remote sensing model based on the space enhancement method, and raises the accuracy that the model estimates, making it operable for high-frequency dynamic monitoring of regional land surface energy and water. And also it expands the application of MODIS data and TM/ETM+data, and raises the data utilization ratio.(5) Finally, it selects the MODIS data for typical days of clear sky having no cloud or less cloud during four seasons in2002and2008, and analyzes the temporal and special pattern of land surface ET in YiLuo River. Research result shows that the major characters of the land surface ET in the studied area are the large differences in regional distribution and the uneven distribution of the year. The land surface ET is greatly influenced by vegetation cover, surface temperature and terrain conditions. Temporal and spatial distributions are also consistent with the changes in these factors.Inside the river valley, the spatial distribution of land surface ET has three characteristics:it has apparent regional differences; the land surface ET is greatly affected by topography; the land surface ET is also under the impact of water supply condition. In addition, the spatial distribution of daily ET is also in accordance with the distribution of different land cover types. The daily ET has a linear correlation with NDVI and surface temperature, has a logarithmic correlation with altitude, and has no significant correlation with slope and aspect. Without considering effects of terrain, the daily ET is a large0.17mm/d on the average, and there is little change in different aspects, increasing with the slope's increasing trend.This is not in accordance with the actual situation in the studied area. Therefore, at mountain area with complicated topography, the terrain factors must be taken into consideration.From the land surface flux and ET changes in the year, the character of seasonal variation is obvious, largest in summer, followed by the spring and autumn, winter in the end. Distribution during the year has a "single peak" trend. The surface net radiation, soil heat flux and daily ET quantity in2008are all higher than those in2002, and differences of daily ET quantity within the year in2008are bigger than those in2002, which shows from2002to2008, the activities of the human beings have an increasing impact in the studied area. There exists a gradual increase in both land surface ET process and ET quantity by the year, and the seasonal variation inside the year is obvious.
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