Research On Estimation Of Net Radiation Using Remote Sensing Data In The Middle Reaches Of Heihe River Basin Over The Tipical Land Surface

Accurate estimation of total net radiation of earth’s surface and other radiation components have special significance to the application of land-based models, such as ecology, hydrology, meteorology, and researches of numerical weather prediction and global environmental change. Observation site of surface radiation can provide the most accurate measurement of surface net radiation flux, but due to the uneven distribution of surface radiation observation site, limited quantity, the instrument maintenance, weather factors, man-made fault and broken underlaying surface etc. affect the normal observation of net radiation, so it is hard to ensure the obtain of long-term net radiation data, which cannot meet the need of climate research, global climate change and research of related fields.Based on the domestic and foreign net radiation studies, this paper established a parameterization schemes that only use the remote sensing data of middle resolution scale to estimate net radiation under sunny conditions. Rely on the MODIS land and atmosphere products and take the midstream of Heihe River as test area, the paper estimated downward shortwave radiation, upward shortwave radiation, downward longwave radiation, upward longwave radiation, net radiation flux, and the average daily net radiation. Further, the paper uses the observation results of Heihe River eco-hydrological remote sensing experiment of Chinese Academy of Cold and Arid Regions to analyze and verify the estimation results. The results show that :(1)Only use MODIS atmospheric and terrestrial products to calculate net radiation is feasible.(2)As to the downward shortwave radiation, RMSE ranges between 16 and 23W·m-2, the accuracy of the calculation is reasonable.As to the upward shortwave radiation, RMSE ranges between 7 and 14 W·m-2, the reason for this phenomenon is that the surface albedo of MODIS are overrated.(3)The estimation of the downward longwave radiation is precise, which is consistent with the ground observation data of site. RMSE ranges between 12 and 21 W·m-2, the major cause of this error is that we used the temperatures of lowest air and dew point temperature substituted the temperature and dew point temperature at the level. RMSE ranges of upward longwave is between 12 and 21 W·m-2, the major cause of this error is overrated and underestimated in various degree, the main causes are surface temperature and downward longwave radiation, but the influence of surface temperature is greater. Therefore, it is a necessity to improve the accuracy of surface temperature parameters for estimating the downward long-wave radiation.(4)Estimation results of net radiation show that RMSE ranges between from 19 and 42W·m-2, which is more accurate compared to the previous studies whose RMSE ranges between 55 W·m-2 and 50 W·m-2. The error is mainly caused by the four components of radiation in that the degree of influence of four components of radiation is different; the sources that caused the error of net radiation are different. Therefore, the accuracy of estimation of net radiation depends on accuracy of four components of radiation.By compared to observation value, it shows that the estimation accuracy is much better when we use sinusoidal model to estimate the average daily net radiation.(5)The model can estimate the net radiation in arid and semiarid regions, which also provides an effective basis in calculating Northwest air interface characteristics of flux exchange. in arid and semi-arid regions.