The Study Of The Estimation Of Downward Radiation Based On MODIS Data

Earth surface downward radiation includes Downward Shortwave Radiation (DSR, 0.3-4μm) and Downward Longwave Radiation,(DLR,4-100μm), is a key role in the sur face radiation balance, a significant driven factor for interactions between surface ene rgy balance and surface climates and also an key input parameter to land surface proc ess and climate shift studies. High accuracy surface downward data is of great signific ance to study human environment and helps also decisions related to human environm ent. Common surface radiation observation stations provide accurate surface radiation fl ux values but limited amounts and expensive maintenance makes traditional surface ra diation observation couldn’t satisfy the studies on human society climate, weather fore cast and other relative aspects. At present, studies on surface downward radiation esti mation remains important.Attributes to the satellite remote-sensing technologizes, radiation balance data with good time continuity and spatial heterogeneity can be used by surface radiation balan ce conveniently. But the data used for estimating downward radiation (DLR\DSR) ba sed on satellite remote-sensing technology in the past are mostly low spatial definition and low spectrum definition data; and scholars are using high-range spectrum data wi th better spatial resolution to calculate the downward radiation benefited by many satel lites-launched by many countries recently, yet not verified and applied. In this article, MODIS data are used as study objective data to estimate downward radiation (DLR\D SR) by considering time resolution, spatial resolution, spectrum resolution and remote-sensing studies done before.At present, mature data set products that estimate the surface downward radiation by using satellite data shares common disadvantages of low spatial resolution, low ac curacy and great uncertainty exists for products quality. Error grows larger among the high altitude area and polar area which fails to satisfy the requirement of surface ener gy balance studies. But the estimation methods by using medium-high resolution greatl y relies on common observation data, and most estimation methods can used only for the sunny weather, surface downward radiation estimation under cloud remains a prob lem now. Basic on downward radiation remote sensing retrieval physical system analys is, according to atmospheric radiative transfer theory, primary downward radiation rem ote-sensitive estimation methods at present are concluded in this article, an surface do wnward radiation(DSR\DLR) estimation model and frame established by using MODIS data is simulated and verified throughout mass radiation and observation data.The result performed from surface downward radiation (DSR\DLR) estimation met hod and frame is taken to compare to three key radiation data GEWEX, ISCCP, and CERES:the average roots-mean-square errors of surface downward shortwave radiation by compared to the GEWEX, ISCCP, and CERES are respectively 76.711W/m2、83.92 95W/m2 and 81.867W/m2, standard errors are -9.132W/m2、-7.7655W/m2 and -8.258W/ m2; average roots-mean-square errors of surface downward longwave radiation by com pared to the GEWEX, ISCCP, and CERES are respectively 76.3805 W/m2.77.461W/m2、 79.9175W/m2 and the standard errors are-7.7655W/m2、-9.082Wm2、-8.542W/m2. On t he other aspect,4 actual downward shortwave radiation data of 4 different surface typ es and 6 downward longwave radiation data from actual station is chosen for verifyin g an as results that surface downward radiation (DSR\DLR) calculated through the me thod and frame mentioned above has achieved high accuracy under all-weather situatio n which meet the requirement of certain study structure. By compared to the statistical data of the GEWEX, ISCCP and CERES results, MODIS estimating method has obvi ous advantages on most statistic indexes, and has higher resolution. At last part of thi s article, key parameters affected on the remote sensing retrieval of the downward rad iation are also analyzed and concluded. The difficulties and problems exists in surface downward radiation estimation methods studies are discussed in the last part, as well as the trending of the surface downward radiation estimation method studies in the f uture.