Evaluation of MODIS Collection 6 aerosol retrieval algorithms over Indo-Gangetic Plain: Implications of aerosols types and mass loading
Evaluation of MODIS Collection 6 aerosol retrieval algorithms over Indo-Gangetic Plain: Implications of aerosols types and mass loading
复制标题
DOI：
10.1016/j.rse.2017.09.016
复制
发表时间：
2017-11
影响因子：
13.5
通讯作者：
Alaa Mhawish;T. Banerjee;D. Broday;A. Misra;S. Tripathi
中科院分区：
文献类型：
--
作者：
Alaa Mhawish;T. Banerjee;D. Broday;A. Misra;S. Tripathi
本研究评估了中分辨率成像光谱辐射计 (MODIS) Collection 6 (C6) AOD 反演算法的性能，包括 3 公里和 10 公里空间分辨率下的暗目标 (DT) 气溶胶光学深度 (AOD)、10 公里处的深蓝 (DB) AOD 以及南亚印度恒河平原 (IGP) 上 10 公里处的合并 DT-DB AOD。总共 14,736 个并置的 Aqua MODIS C6 AOD 在 550 nm 处与来自 IGP 上的 6 个 AERONET 站的 AOD 进行了评估，这些 AOD 在 2006 年至 2015 年卫星立交桥（± 1 h）期间测量。检查了气溶胶不均匀性（在气溶胶负荷和气溶胶类型方面）对星载 AOD 反演不确定性的影响。两种分辨率（3 公里和 10 公里）的 DT 算法将 AOD 高估了 14-25%，只有 51.37-61.29% 的检索结果落在预期误差 (EE) 范围内。与 DT 10 km 算法相比，DT 3 km 算法低估了表面反射率，后者在搭配数量和检索精度方面都优于前者，尤其是在城市地区。即使在低气溶胶负荷条件下，DB 10 km 也能够检索干旱/沙漠地区和植被表面的 AOD。然而，它的性能仍然很差，检索准确率为 53.76%，RMSE 较低（0.214），并且整个 IGP 的 AOD 普遍被低估。合并的 DT-DB AOD 产品主要以 DT 检索为主（73%–100%），除了明亮的陆地表面之外，并且 56.03% 的合并 DT-DB 检索落在 EE 内。研究发现 MODIS C6 产品的反演精度很大程度上取决于估计的表面反射率和气溶胶类型。在 IGP 中，DB 更好地预测了表面反射率，而 DT 在两种分辨率下都不同程度地高估了表面反射率。对于气溶胶尺寸变化的高气溶胶负荷条件，10 km DT 的反演精度灵敏度较低，而 3 km DT 的反演精度在估计表面反射率时表现出较大的不确定性。相比之下，DB 10 km 显示出更大的偏差，具体取决于气溶胶大小。对于以精细或混合气溶胶为主的非常高的气溶胶负载条件，所有算法在气溶胶模型中都存在错误。 DT 10 km、DB 10 km 和合并的 AOD 在阈值水平内几乎相同，而 DT 3 km 在检索精度和 RMSE 方面表现最差。我们得出的结论是，在 IGP 中，DB 10 km AOD 在检索精细模式气溶胶方面具有最高的精度，而 DT 10 km AOD 在检索不同气溶胶类型方面具有几乎相同的精度。对于粗粒为主的气溶胶，当 DT 和 DB 之间的差异保持最高时，发现合并的 AOD 在跨 IGP 反演 AOD 方面具有更高的准确性。
This study evaluates the performance of MODerate resolution Imaging Spectroradiometer (MODIS) Collection 6 (C6) AOD retrieval algorithms, including Dark Target (DT) aerosol optical depth (AOD) at 3 and 10 km spatial resolutions, Deep Blue (DB) AOD at 10 km, and the merged DT-DB AOD at 10 km across the Indo-Gangetic Plain (IGP), South Asia. A total of 14,736 collocated Aqua MODIS C6 AOD at 550 nm were evaluated against AOD from six AERONET stations over IGP, measured during the satellite overpass (± 1 h) from 2006 to 2015. The effects of aerosol heterogeneity, in terms of both aerosol loading and the aerosol type, on the uncertainty of the satellite-borne AOD retrieval were examined. The DT algorithm at both resolutions (3 km and 10 km) overestimated the AOD by 14–25%, with only 51.37–61.29% of the retrievals falling within the expected error (EE). The DT 3 km algorithm underestimates the surface reflectance in comparison to the DT 10 km, with the latter outperforming the former both in terms of number of collocations and retrieval accuracy, especially over urban areas. The DB 10 km was able to retrieve AOD over both arid/desert regions and vegetated surfaces even under low aerosol loading conditions. Yet, its performance was still poor, with retrieval accuracy of 53.76%, low RMSE (0.214), and generally underestimated AOD across the IGP. The merged DT-DB AOD product was mostly dominated by DT retrievals (73%–100%), except over bright land surfaces and 56.03% of the merged DT-DB retrievals fell within the EE. The retrieval accuracy of MODIS C6 products was found to be strongly dependent on the estimated surface reflectance and the aerosol type. Across IGP, DB predicted the surface reflectance better while DT at both resolutions overestimated the surface reflectance at varying extent. For high aerosol loading conditions with varying aerosol size, retrieval accuracy of DT 10 km poses lower sensitivity while DT at 3 km exhibits larger uncertainty in estimating surface reflectance. In contrast, DB 10 km shows greater bias that depends on the aerosol size. For very high aerosol loading conditions, dominated by fine or mixed aerosols, all the algorithms have errors in the aerosol model. The DT 10 km, DB 10 km and the merged AOD performed almost equally within the threshold level while the DT 3 km showed the poorest performance in terms of retrieval accuracy and RMSE. We conclude that across IGP, DB 10 km AOD has the highest accuracy in retrieving fine mode aerosols while DT 10 km AOD has almost identical accuracy in retrieving varying aerosol types. For coarse dominated aerosols, when the dissimilarity between DT and DB remains highest, the merged AOD is found to have higher accuracy in retrieving AOD across IGP.