The Retrieval Of Land Surface Temperature And The Research Of The Evapotranspiration Estimation In The Low Hilly Region Of Red Soil

The ground evapotranspiration is an important link of the moisture exchange between surface and atmosphere,while the surface temperature is an indispensable parameter in the estimation of ground evapotranspiration.Therefore,it is important to select the most suitable method of surface temperature inversion to improve the estimation accuracy of ground evapotranspiration,which is of great significance helping understand the balance of water and energy balance in the low hilly region of red soil,so as to provide guidance for local cropping pattern planning,improving the rational utilization of regional water resource,and increasing the economic efficiency of crops.In this paper,the study area is located in the typical low hilly region of red soil,in Yingtan City,Jiangxi Province.Based on Landsat-8 satellite images combined with ground observation data and DEM digital elevation,land surface parameters were retrieved.By using Jimenez-Munoz&Sobrino single-channel algorithm,single-window algorithm and split-window algorithm for Landsat-8,the results were analyzed and compared,and the algorithm with the highest accuracy was selected.Finally,the METRIC model was used to estimate the daily evapotranspiration in the low hilly region of red soil.According to the land classifications,the temporal and spatial distribution of the evapotranspiration and the surface energy variations were analyzed,and the suitability of the model in the low hilly region of red soil was finally discussed.The main conclusions are as follows:(1)The study found that there were significant spatial and temporal changes in land surface parameters under different land-cover types;The result of the vegetation coverage met the relationship of September 27th>June 23rd>July 25th,which was related to the different growth phases of the crops;The result of the albedo met the relationship of September 27th>June 23rd>July 25th,which was mainly related to the annual change of the solar declination and soil moisture content.In general,when in a vigorous growth period,the higher the vegetation coverage was,the lower the surface albedo was;where the vegetation coverage was small,the higher the soil moisture content was,the lower surface albedo was;while the solar declination decreases,the surface albedo decreases too.(2)The overall trends of spatial-temporal change of the land surface temperature among three methods tend to be consistent,there was difference in the value of land surface temperature.For mean land surface temperature,the results met the relationship of split-window algorithm?mono-window algorithm?single-channel algorithm;the average surface temperature met the relationship July 25th ? June 23rd ?September 27th.For different land-cover types,generally land surface temperature met the relationship of urban?vegetation ?water.As a whole,for different vegetation,higher vegetation coverage was followed by lower surface temperature.When the value of vegetation coverage was almost same,the higher water content was followed by the lower the surface temperature;the difference among methods was the smallest when in water,and the largest when in urban;the absolute error and RMSE are the smallest when between the single-window algorithm and the measured value.(3)There are significant spatial and temporal differences in net radiation flux,soil heat flux and sensible heat flux.In general,each energy balance component met the relationship of June 23rd ?July 25th ?September 27th;the net radiation under different land-cover types showed the relationship of water?rice? orange gardens?dry-plant?urban.The soil heat flux showed water?urban? dry-plant?rice?orange,while sensible heat flux showed urban?dry-plant>orange>rice>water;the bigger the solar declination was the higher net radiation flux was.However the higher the soil moisture content was,the lower the proportion of sensible heat flux of net radiation was,and the smaller the soil heat flux was.At the same time,the higher the vegetation coverage of the surface was,the higher the net radiation flux was,while the smaller the soil heat flux and sensible heat flux are.(4)The temporal relationship of evapotranspiration by METRIC model was July 25th>June 23rd>September 27th.As for different land-cover types,it showed that water>rice>orange>dry-plant>urban.The evapotranspiration was related to temperature,vegetation growth and soil moisture content.The higher the temperature was,the greater the evapotranspiration was.The correlation between evapotranspiration and air temperature was greatest in the land types of water and town.The evapotranspiration of the same crop in the vigorous growth stage was greater than the initial growth stage;when same crop was in the same growth stage,the greater the soil moisture content was,the greater the evapotranspiration was.