Fig. 1. The maps of Weihe and Xiashan reservoirs

Fig. 2. Optimization SVR model using SA-PSO

Fig. 3. Measured reflectance spectra (a); and normalized spectra (b)

Fig. 4. Pearson’s correlation coefficient (r) between band ratios R_rs(λ₂)/R_rs(λ₁) and COD in the spectral range of 466~940 nm

Fig. 5. SA-PSO-SVR accuracy evaluation

Fig. 6. Evaluations of predictions using SVR, BP neural network and LR method

Fig. 7. Spatial distribution of COD concentration obtained from OHS data