Fig. 7
Correlation diagram of spectral derivatives and logarithmic transformations. (a) first-order derivative; The black line represents the correlation between pH and the spectral bands after preprocessing and first-order derivative. The red line represents the correlation between CODcr and the spectral bands after preprocessing and first-order derivative. The blue line represents the correlation between TP and the spectral bands after preprocessing and first-order derivative. The orange line represents the correlation between NH3-N and the spectral bands after preprocessing and first-order derivative. The purple line represents the correlation between TN and the spectral bands after preprocessing and first-order derivative. The green line represents the correlation between Chl and the spectral bands after preprocessing and first-order derivative. (b) second-order derivative; The WQI indicated by the line colors are the same, but the spectral bands are preprocessed and second-order derivatived. (c) third-order derivative; The WQI indicated by the line colors are the same, but the spectral bands are preprocessed and third-order derivatived. (d) logarithmic first-order derivative; The WQI indicated by the line colors are the same, but the spectral bands are preprocessed and logarithmic first-order derivatived. (e) logarithmic second-order derivative; The WQI indicated by the line colors are the same, but the spectral bands are preprocessed and logarithmic second-order derivatived. (f) logarithmic third-order derivative. The WQI indicated by the line colors are the same, but the spectral bands are preprocessed and logarithmic third-order derivatived. Values above the solid line indicate a strong correlation between the band and the WQI. Values above the dashed line indicate a stronger correlation between the band and the WQI.
