利用AB算法进行高分四号卫星数据反照率反演

Retrieval of GF-4 Satellite Image Data Surface Albedo Based on Angular Bin Algorithm

  • 摘要: 地表反照率(Albedo)是地表能量收支平衡的重要地表参数。作为新近发射的地球同步轨道卫星,高分四号(GF-4)卫星拥有优于同类卫星的高时间高空间分辨率,然而由于其观测角度单一,基于双向反射分布函数(bidirectional reflectance distribution function,BRDF)的传统反演方法难以实现地表反照率的精确快速反演,因此采用基于单一观测角度的角度格网法(angular bin,AB1)。首先,利用先验的多角度地球反射极化和方向测量仪(POLarization and Directionality of the Earth’s Reflectances,POLDER)卫星观测数据,建立反照率与某一方向反射率之间的经验关系;然后,利用POLDER卫星和GF-4卫星的光谱响应函数与光谱库数据,将该经验关系转换为基于GF-4卫星的反照率与反射率经验关系(即查找表);通过输入单一角度的GF-4卫星反射率数据,得到GF-4卫星反照率结果;最后,利用中分辨率成像光谱仪(Moderate-resolution Imaging Spectroradiometer,MODIS)与Landsat 8地表反照率结果对反演结果进行交叉验证。结果表明,MODIS反照率与GF-4反照率的均方根误差(root mean square error,RMSE)为0.027 3,Landsat 8反照率与GF-4反照率的RMSE为0.017 6,说明基于AB1算法的反照率反演结果精度可靠,这对于GF-4卫星的反照率产品生产具有一定的应用意义。

     

    Abstract: Albedo has important significance to the research of the surface energy balance and climate. GF-4 satellite is the earth synchronous orbit satellite, whose spatial resolution is 50 m, much better than other same orbit satellites. Because GF-4 only has one observation angle on a site, it's difficult to use bidirectional reflectance distribution function (BRDF) inversion method to retrieve the albedo. So, we use angular bin (AB1) algorithm to retrieve the albedo. AB1 is based on priori knowledge. Firstly, we use the data of Polarization and Directionality of the Earth's Reflectances (POLDER) to found the empirical explanation between albedo and the reflectivity of one angle, and then convert POLDER's empirical explanation to GF-4 by the spectral response functions of POLDER and GF-4.Next Plug in one GF-4's image and calculate the albedo using the empirical explanation. Last we use MODIS and Landsat 8 albedo products to verify the calculation results. The results show that the root mean square error (RMSE) of MODIS albedo and GF-4 albedo is 0.027 3, the RMSE of Landsat 8 albedo and GF-4 albedo is 0.017 6, verify that the accuracy of albedo inversion based on AB1 is reliable, proving that using the AB1to retrieve the GF-4's albedo has good precision.

     

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