利用MODIS资料计算不同云天条件下的地表太阳辐射

Estimation of Surface Solar Radiation Using MODIS Satellite Data and RSTAR Model

利用MODIS气溶胶和云产品卫星数据与大气辐射传输模式RSTAR,进行了晴空和有云条件下地表太阳辐射计算,并与香河综合辐射站的地基辐射测量值相比较。分析表明,晴空下二者相关性较好,相关系数平方R^2值为0.95,均方根误差RMSE为38.8 W/m^2。有云条件下,计算结果较差于晴空条件下,R^2值为0.88,RMSE为88.2 W/m^2。观测显示,香河站云—气溶胶共存现象较多,而MODIS仅按单一层的云进行微物理参数反演,导致模式输入参数误差,给地表太阳辐射计算结果引入误差。为了分析云-气溶胶共存状态对计算地表太阳辐射的影响,利用RSTAR计算了不同光学厚度的云和气溶胶在特定波段卫星观测的辐亮度值,并对于特定波段卫星接收的辐亮度值,用不同垂直结构的云和气溶胶分别反演其光学和微物理参数,再利用反演的结果分别计算相应的地表太阳辐射。结果表明:相对于单一云层的反演结果,云下气溶胶光学厚度(AOD)为0.1时,由反演误差所导致的地表太阳辐射估算误差较小;而随着AOD增加影响明显增大,在AOD为1.2时,相对误差达17.79%~18.38%。对于污染较重的华北地区而言,分析云覆盖下的气溶胶对地表太阳辐射的影响,有助于提高有云条件下地表太阳辐射的计算精度。

The MODIS aerosol product and cloud product data are combined with the atmospheric radiation transmission model RSTAR to calculate the surface solar radiation under sunny and cloudy conditions.The results are compared with the ground observed values of Xianghe integrated radiation station.It shows that the simulated value and observed value have good correlation.The R^2 and RMSE are 0.95 and 38.8W/m^2 in the clear skies,while 0.88 and 88.2 W/m^2 in the cloudy skies.The results show that more cloud-aerosol mixed states is in Xianghe station,while MODIS can only invert single microphysical parameter of cloud layer,which leads to error of model input parameter,bringing error to the calculation result of surface solar radiation.In order to quantitatively analyze the effect,the RSTAR radiation model was used to calculate the radiance values,and invert f different cloud and aerosol optical thickness,calculating surface solar radiation.The results show that the error of estimation of surface solar radiation is 1.29%-1.56% when the aerosol optical thickness（AOD）is 0.1,compared with the single layer.With the increase of AOD,the effect of AOD increased obviously.The relative error was 17.79%-18.38% when AOD was 1.2.For the heavily polluted areas of North China,it is important to analyze the influence of aerosol on the surface solar radiation under cloud cover,which is very important to improve the calculation accuracy of surface solar radiation under cloud conditions.