有机污染物是水体污染的主要来源, 水体有机污染程度可通过化学需氧量(COD)指标综合表示。 与传统复杂专业的化学检测手段相比, 遥感技术因具有快速、 实时、 非接触、 大面积等独特优势而广泛用于水体水质监测, 包括叶绿素、 悬浮物和黄色物质等生色参数的定量反演。 然而目前对于水体COD这一重要水质参数的遥感反演报道不足, 这主要是因为影响COD浓度的有机污染物复杂多变、 光谱响应机理尚不明晰。 通过测量实验室配比的不同浓度COD标准液及野外实际水体的可见-短波红外反射光谱（350～2 500 nm）, 分析了水体COD的光谱响应特性。 研究发现, 随着COD浓度增加, 水体反射光谱在可见-短波红外范围内整体逐步上升, 但在540～580和1 000～1 060 nm波段范围内光谱响应快速增强, 表现出—OH伸缩振动的三级倍频和—CH伸缩振动与变形振动的合频吸收特征。 利用上述敏感谱段与全谱段分别对实验室COD标准液和野外实际水体建立偏最小二乘（PLS）回归模型, 其中, COD标准液模型反演精度: (1）敏感谱段, R2=0.972, RMSE=39.629 mg·L-1; (2）全谱段, R2=0.961, RMSE=46.639 mg·L-1; 实际水体模型反演精度: (1）敏感谱段, R2=0.798, RMSE=32.037 mg·L-1; (2）全谱段, R2=0.658, RMSE=48.332 mg·L-1。 结果表明, 不管是COD标准液还是实际水体, 基于敏感谱段的COD反演模型精度均优于基于全谱段的反演模型。 研究可为水体COD遥感反演提供重要的理论与技术支撑。

Organic pollutants are the main source of water pollution. The degree of organic pollution in water bodies can be comprehensively reflected by chemical oxygen demand (COD) indicator. Compared with the traditional methods, which are highly time-consuming and cause secondary pollution, remote sensing techniques can detect water COD quickly and effectively, particularly over large areas. However, due to complex composition of COD, detecting water CODusing remote sensing technology is still insufficient, and the spectral response mechanism of COD in the visible-short-wave infrared range is not yet clear. To clarify the spectral response mechanism of water COD, the reflectance spectra of 45 different concentrations of COD standard solution (potassium hydrogen phthalate) were measured by using PSR hyperspectral instrument in the laboratory simulation environment in this study. The continuum removal and reflectance normalization methods were used to analyze the spectral characteristics of COD standard solution with different concentrations, and results showed that with the increasing of COD concentration, the water reflectance spectra increased gradually in the visible-short-wave infrared range, as well as the spectral response increased rapidly in the range of 540～580 and 1 000～1 060 nm, showing the three-stage frequency doubling of —OH stretching vibration and the combined frequency absorption characteristics of —CH stretching vibration and deformation vibration. In order to further verify the effectiveness of sensitive bands, the partial least squares (PLS) regression models were developed by using sensitive bands and full bands, respectively. The correlation coefficient and RMSE of COD standard solution based on the sensitive bands were 0.972 and 39.629 mg·L-1, respectively, while the correlation coefficient and RMSE based on full bands were 0.961 and 46.639 mg·L-1, respectively. It showed that for COD standard solution that is not interfered byexternal factors, high accuracy can be achieved with only a small number of sensitive bands, even higher than the full bands model. The model retrieval accuracy based on the sensitive bands was also significantly better than the accuracy based on full bands when the model are applied to the field-measured water spectra. The results suggested that using the 540～580 and 1 000～1 060 nm sensitive bands can effectively improve the accuracy of detecting water COD, and significantly advance our ability for large-area rapid monitoring of COD using remote sensing in practical cases.