基于遥感手段准确估算水体漫射衰减系数Kd(490), 可为有效评价近岸海域水质、准确估算真光层深度提供有力数据和方法支撑。利用2004~2012年在南海海域获得的9个航次的实测Kd(490)数据, 通过建立实测与遥感产品的时空匹配数据对, 获取与Kd(490)实测数据相对应的MODIS-Aqua遥感反射率(Rrs(λ))和叶绿素a浓度(Chl-a)产品, 分别采用算法Muller, Werdell, Morel, Lee和MODIS业务化算法KD2M对南海海域Kd(490)遥感产品进行精度评估与对比; 在此基础上, 考虑到南海海域水体的特异性, 基于相应的实测Rrs(λ)和Chl-a数据集, 利用上述算法对Kd(490)反演产品再次进行精度评估与对比, 进而探讨Kd(490)产品的误差来源和算法区域化修正的必要性。基于MODIS-Aqua遥感产品, 利用上述五种算法获得的MODIS-Aqua Kd(490)产品值与实测值的平均相对误差(APD)分别是2012%, 2922%, 17.98%, 22.61%和21.61%, 其中, Morel算法最优, 且相关系数最高达0.5; 基于相应实测数据, 利用上述算法反演获得的Kd(490)产品精度均有不同程度的提高, 特别是算法Lee和Werdell, APD分别为17.86%和1797%, 提高了5%~11%, 最优算法为Morel, 其APD可达15.44%。合理选取评估算法及进一步开展算法的区域性修正对于准确估算南海海域Kd(490)产品是非常必要的。

The diffuse attenuation coefficient of downwelling irradiance Kd(490) is of great value for evaluating the coastal water quality and estimating the optical depth accurately. In this paper, the performance of MODIS-Aqua Kd(490) products derived using the algorithms of Muller, Werdell, Morel, Lee, and KD2M with MODIS-Aqua remote sensing reflectance Rrs(λ) and Chl-a products were compared in the South China Sea (SCS) based on the relaxed match-ups between MODIS-Aqua products and in situ data collected from 2004 to 2012. Further, taking into account the unique optical properties of the SCS waters, the performance of Kd(490) products derived using the above algorithms with field reflectance Rrs(λ) and Chl-a data were evaluated in order to analyze the causes of the uncertainties of Kd(490) products and the necessity of regional algorithm optimization. The results show that MODIS-Aqua Kd(490) products derived using the algorithms of Muller, Werdell, and Morel with MODIS-Aqua Rrs(λ) and Chl-a products underestimated the in situ data, while the algorithms of Lee and KD2M overestimated the data, with average relative errors (APD) of 20.12%, 29.22%, 17.98%, 22.61%, and 21.61%, respectively. The algorithm of Morel performed the best, with a coefficient of determination R2 of 0.5. There are significant improvements in the accuracy of the above algorithms by using field Rrs(λ) and Chl-a data, especially for the algorithms of Werdell and Lee, with an APD of 5%—11% improvement. The algorithm of Morel performed the best, with an APD of 15.44%. It is necessary to choose the proper algorithm and conduct algorithm regionalization correction for the accuracy estimation of Kd(490) products in the SCS.