Net Radiation Flux Estimated Based on MODIS Products over the Semi-Arid Loess Plateau
Using the first level products of Moderate-Resolution Imaging Spectroradiometer (MODIS) and three algorithms to estimate the shortwave radiation, longwave radiation and net radiation of Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) from April to August in 2007, and further the coefficients of WKC algorithm were modified using observed data of SACOL from June to August in 2006.Compared to the observed values, the result showed that the accuracy of estimated shortwave radiation was better than longwave radiation in the satellite transit time.Based on the components of the surface radiation, the accuracy of estimated net radiation was good, and the minimum mean absolute percent error was 9.98％ in the satellite transit time.The daily net radiation which obtained by using the time scale expansion method was close to the measured data, and the mean absolute percent errors were less than 25.0％.The daily net radiation which estimated based on the shortwave radiation directly was deviated from the observed value, but the correlation was good.However, the result had improvement after it was modified by the measured data of SACOL, and the deviation between the estimated result and observed one was the minimum.It was worth noting that each radiation component was can be retrieved by MODIS products directly and did not need any other auxiliary data, and accuracy of estimated net radiation was only after the modified algorithm in the satellite transit time.The biggest advantage of the algorithm which estimated net radiation based on the shortwave radiation directly was avoid the longwave radiation estimated, and the accuracy of the algorithm was better after it was modified by the observed value, but it required measured auxiliary data.So, in the case of having the ground observed data, the net radiation can be estimated by using the modified algorithm based on the shortwave radiation.In the case of absence the ground observed data, it provides an effective way to estimated the net radiation by estimating the radiation components.
Net radiationShortwave radiationLongwave radiationMODISSACOL
NETL
NSTL
万方数据
维普
