Research On Spatial Downscaling Method Of Downward Surface Shortwave Radiation With Coarse Spatial Resolution

Also known as solar radiation,the Downward Surface Shortwave Radiation(DSSR)is the integral of solar radiation in the shortwave band below 4um.DSSR is one of the important parameters in the process of surface radiation estimation and the establishment of many land surface models.The spatial and temporal variation of DSSR largely controls the surface temperature change,hydrological cycle and net primary productivity of land,and influences and then regulates the earth's climate change and global energy balance.Therefore,it is necessary to carry out the research on agriculture,climatology,ecology and hydrology.In addition to the traditional ground station observation,satellite remote sensing has gradually become an important method to estimate DSSR.At present,there are many kinds of DSSR products at home and abroad,but their spatial resolution is often several kilometers or even tens of kilometers.Although some high-resolution remote sensing satellite data can obtain high-resolution DSSR data,they are faced with the influence of low time resolution,and cannot realize the long-term dynamic monitoring of DSSR.Northeast Spain and part of the Pyrenees mountains were selected as the research area,according to the theory of downward surface shortwave radiative transfer and radiative transfer in the process of scale invariance,on the basis of establishing the cloudless condition and under the condition of a cloud of DSSR spatial downscaling parameterized scheme of coarse spatial resolution to downscaling DSSR product data,and get real surface for terrain correction DSSR high marks on the surface of the downscaling results.At the same time,the downscaling results are evaluated and verified.The verification and evaluation of the downscaling results under cloud-free conditions include the visual effect assessment at different times and in different seasons,the spatial distribution assessment of the real ground surface DSSR with different slopes downward,and the verification and evaluation of the daily sequence downscaling results compared with the measured data at the surface site.The results of annual series downscaling under cloud conditions were evaluated visually and compared with the measured data of ground stations.The results show that the correlation between the DSSR downscaling results of daily sequence and the DSSR downscaling results of annual sequence under cloud-free conditions is relatively high,and the visual effect is substantially improved.The measurement coefficient R~2 and root mean square error(RMSE)of DSSR downscaling results are improved.In general,the research results of this paper can be used as a new method to obtain reliable and high-resolution DSSR data from coarse resolution DSSR products under cloudless and cloud conditions,respectively.This paper has the following innovative points:(1)In this paper,based on MSG DSSR product data and ALOS DEM high-resolution terrain data collected by the second generation of European stationary meteorological satellite,the DSSR downscaling method under corresponding weather conditions was proposed respectively,considering the different transmission processes of downward surface shortwave radiation under cloud-free and cloudy conditions.(2)In cloud-free weather,using the scale invariant in the process of radiative transfer relationship,establish the coarse-resolution(DSSRc)and high-resolution(DSSRh)between the parameterization scheme,the downward shortwave total radiation is decomposed into direct radiation and diffuse radiation on the surface of the horizontal component,respectively based on the parameters of direct radiation and diffuse radiation downscaling to horizontal surface,then introduces horizontal surface radiation component terrain parameters for terrain correction for high-resolution real surface DSSR.(3)Based on the basic idea of the cloud-free downscaling model,some algorithms were optimized,and the ratio weight between cloud-free and cloud pixels in landsat-8 radiation luminance data was used to approximate the cloud transmissibility,and the weight information was weighted to the coarse resolution pixel(DSSRc).At the same time,a 3×3 smoothing window was used to smooth the MSG DSSR raw data with large spatial heterogeneity,and the downward surface shortwave radiation under cloud conditions with cloud elements was estimated,and then the DSSR downscaling method under cloud conditions was proposed.