Estimation Of Daily Shortwave Solar Radiation Based On Himawari-8 And Sentinel-2 Satellites

Downward surface shortwave radiation(DSSR)is the primary source of energy on the earth,and a significant input parameter for the simulation models of land surface processes such as ecology,hydrology,and climate.Satellite remote sensing data can provide continuous spatio-temporal information of the atmosphere and surface,and is an important data source for global or regional daily DSSR research.The polar-orbiting satellites have high spatial resolution and low temporal resolution characteristics,while geostationary satellites with high temporal resolution and low spatial resolution.It is becoming a hot research topic which aims to obtain high spatial resolution daily shortwave solar radiation by taking respective advantages of polar-orbiting satellites and geostationary satellites.The methods of obtaining daily DSSR based on the spatial downscaling of geostationary satellite radiation products and the temporal extrapolation of polar-orbiting satellite data are mainly study in this paper mainly studies.The specific research content and main conclusions are as follows:(1)In the middle and upper reaches of the Heihe River with large spatial heterogeneity of DSSR,10 min radiation product(5 km)of the geostationary meteorological satellite Himawari-8(H-8)is spatial downscaled to 50 m,and then the downscaling results ware integrating to obtain daily average DSSR.The accuracy of 50 m H-8 spatial downscaling results is verified by selecting 3,002 sample data from 6 radiation sites in the middle and upper reaches of the Heihe River.The results show that the 10 min H-8 DSSR downscaling data has high accuracy,the average determination coefficient(R~2)is 0.98,the mean bias error(MBE)is 40.95 W/m~2,and the root means square errors(RMSE)is 69.00 W/m~2.The daily average shortwave solar radiation after integrating the downscaling results also has high accuracy.The R~2 of the 45 sample data is 0.96,the MBE is 41.57 W/m~2,and the RMSE is 49.25W/m~2.In general,the accuracy of both the spatial downscaled 10 min and daily average DSSR is higher than that of the corresponding radiation remote sensing products,and it can present more detailed information on the temporal and spatial variations of the surface shortwave solar radiation.(2)In the Laohugou of Qilian Mountains,the high spatial resolution Sentinel-2(10 m)instantaneous DSSR data is expanded to daily through the sinusoidal model,and Sentinel-2 10 min and daily average shortwave solar radiation are obtained respectively.The verification result shows that the 10-minute estimation result is consistent with the diurnal variation trend of shortwave solar radiation observed on the ground,R~2 is 0.97,MBE is 30.97 W/m~2,and RMSE is 93.76 W/m~2.The temporal-extrapolation of daily average DSSR has high accuracy,and the MBE and RMSE of the 52 sample data are 41.06 W/m~2 and 88.90 W/m~2,respectively.(3)The accuracy of the two daily DSSR estimation methods was compared using the measurement from the Laohugou No.12 Glacier site.Due to the limitation of data acquisition,the clear sky data on August 17,2018,was selected for verification.The results show that the H-8 spatial downscaling method(R~2=0.96,MBE=-2.39 W/m~2,RMSE=76.69 W/m~2)has better accuracy than the Sentinel-2temporal extrapolation method(R~2=0.97,MBE=10.70 W/m~2,RMSE=95.97 W/m~2)at 50 m spatial scale.However,the spatial resolution of Sentinel-2 original shortwave solar radiation is 10 m,which can show more detailed information than 50 m H-8spatial downscaling DSSR data.