Abstract: Sunshine duration was an important indicator for light resource in agricultural climate resources.In fact,terrain masking should be considered in the extrapolated model in order to acquire the refine national sunshine duration data in the actual terrain.The model which could automatically calculate astronomical sunshine duration in the actual terrain was established based on the 1∶250000 Digital Elevation Model(DEM) data.The sunshine grid data sets of the national actual terrain of each ten days,monthly,quarterly and annual time scale were got respectively,based on the sunshine duration data from 2346 national weather stations from 1971-2000.The calculated values and measured data from 2346 stations were compared.The results showed that the annual sunshine duration value,considering terrain masking,was slightly smaller than the measured value.The MAE of the extrapolated annual sunshine time was 61.6h,the RMSIE was 78.7h,and the average relative error was 2.9%.The calculated error was higher with the terrain more intense,the calculated error was smaller with the solar elevation angle larger.

Key words: Terrain masking, Terrain masking, Sunshine duration, Refinement project