利用中分辨率成像光谱仪(MODIS)的一级数据产品,通过三种不同的方法(两种通过估算各辐射分量来得到净辐射和一种直接通过短波辐射得到净辐射的方法)估算了2007年4 — 8月兰州大学半干旱气候与环境监测站(SACOL)的短波辐射、长波辐射和净辐射值,进一步利用2006年6—8月SACOL站实测资料对第三种方法的系数进行修正,并将不同方法估算的净辐射与实测资料进行对比。结果表明,在MODIS一级数据产品基础上,估算的卫星过境时刻短波辐射精度较高,长波辐射稍差;在各辐射分量基础上得到的卫星过境时刻的净辐射较好,平均相对误差最小为9.98%,且通过时间尺度扩展得到的净辐射与实测值较为接近,平均相对误差<25.0%;而使用短波辐射直接估算的净辐射较实测值偏大,但相关性较好;在利用实测数据对算法进行修正后得到的SACOL站净辐射较修正前有了较大的改善。值得注意的是,卫星过境时刻各辐射分量的计算不需要任何地面观测资料辅助,计算过程需要的所有参数可以直接由MODIS数据反演,且该方法得到的净辐射精度仅次于修正后的方法,普适性较好,所以,在缺乏地面观测资料的情况下,这种方法可以为大尺度的净辐射估算提供一条有效途径。而通过短波辐射直接估算净辐射的方法,其最大的优势就是避免了长波辐射的估算,可以直接利用短波辐射估算净辐射,对该方法的经验系数局地修正后估算的结果更优,但这种方法需要地面观测资料的辅助,所以在有地面观测资料的情况下,可以通过修正模型的系数获得更高精度的净辐射。
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.
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