Research Of Evapotranspiration Of Grassland Based On TM Data

Evapotranspiration(ET)is the key process of the hydrological cycle.It provide import basis for using of effective water resource,estimating of grassland ecological environment and maintaining of balance of water.Estimating or simulating ET values accurately have the great significance for many fields,such as raising water resource use efficiency and its temporal and protecting ecological environment.This paper selects Xilin River Basin as the case study that is typical grassland in China,and calculates ET by technology of "3S".The research contents are summarized as follows:(1)Calculation of Land Surface Parameters.According to the actual condition of Xilin River Basin,choosing Qin zhihao's optimized method to calculate the surface emissivity,and results vary from 0.972 to 0.975.Analysing the results,we can find the soil type of Xilin River Basin mainly is light chestnut soil,which show the ecological environment of Xilin River Basin is in a drought of condition.Mono-window algorithm,which is less applied on SEBAL model around the world,can be used to determine land surface temperature,the results alternate between 288.32K and 321.02K,and the maximum value is mainly distributed in the dry areas of less vegetation and surrounding towns.In conclusion,mono-window algorithm is relatively high precision.(2)Model Establishing and Analysing.Use the TM data to establish the basin grassland ET inversion model,the result shows that the basin day ET values range from 0 to 9mm per day and the mean value is 1.5mm per day.The basin has more precipitation and larger evaporation in the period of TM data collection,but the 70%areas of the basin day ET values merely alternate between 0 and 2 mm per day.Analysing the results,we can infer that the shortage of regional water resources space distribution is the main reason for the smaller in ET value.The day ET value is greater than 5mm per day in some areas where are mainly distributed in the surrounding region of Xilin River main stream and tributary and its upstream Dalinuer Lake,and the investigation paper found that surface water resources are relatively rich around these areas.(3)Correlation Analysis.Correlation coefficient can be calculated by the data of day ET values and land surface parameters from choosing 100 of random pixel points,the results show that the relationship between the surface emissivity and day ET value is positive,both surface albedo and surface temperature are inversely relate to day ET value,but the variability of surface temperature has more influence on ET value,because its negative correlation value is-0.971.(4)Using FAO PPP-17 Penman Formula to Verify the Model.Comparing and analysing typical pixel,the outcome of SEBAL model simulation and the results of FAO PPP-17 Penman formula calculation have good consistency,but it is much better to use SEBAL model to simulate the actual condition of regional ET process.The result produces a new thought and method for studying the space-time transformation of ET on grassland in China.This view has certain innovation.With the continuous development of remote sensing technology,inversion model based on remote sensing technology will be more applied to ET inversion,especially in the area which is short of hydrological and meteorological data.The model inversion results have greater significance on the quantification of water resources management,the improvement of water and grass resources use efficiency,achieving the water-glass-livestock system balance.