Fig. 1. Two-dimensional chromaticity diagram and measured hyperspectral chromaticity angle information

Fig. 2. Results and verifications of multi-spectral hue angle inversion method and hyperspectral inversion method based on optimal bands of different sensors. (a)(b) Comparison of results of MODIS modeling and verification; (c)(d) comparison of results of SeaWiFS modeling and verification

Fig. 3. Scatter plot of α varying with Z_sd and leave-one-out cross-validation accuracy of Z_sd. (a) Scatter plot of α varying with Z_sd and fitted curve; (b) Z_sd accuracy plot

Fig. 4. Scatter plot of α versus mass concentration of SPM_{and leave-one-out cross-validation accuracy for mass concentration of SPM. (a) Scatter plot of α varying with mass concentration of SPM and fitted curve; (b) accuracy plot of mass concentration of SPM}

Fig. 5. Scatter plots of α varying with a_ph and leave-one-out cross-validation accuracy for a_ph. (a) Scatter plot of α varying with a_ph and fitted curve; (b) a_ph (443) accuracy plot; (c) a_ph (670) accuracy plot

Fig. 6. Seasonal mean spatial distributions of α in offshore China from 1998 to 2020. (a) Spring; (b) summer; (c) autumn; (d) winter

Fig. 7. Monthly average distribution trends of normalized hue angle, mass concentration of Chl-a, and mass concentration of SPM in China offshore from January 1998 to December 2020. (a) S1 sea area; (b) S2 sea area; (c) S3 sea area; (d) S4 sea area; (e) S5 sea area

Fig. 8. Distribution maps of hue angle and FUI seasonal average frequency in China offshore from 1998 to 2020. (a) Spring; (b) summer; (c) autumn; (d) winter

Fig. 9. Fitting curves and box distributions of measured marine environmental parameters and FUI. (a) Measured Z_sd; (b) measured SPM mass concentration

Fig. 10. Measured a_ph corresponding to 3‒9 levels of FUI in visible band (solid lines represent median, and upper and lower boundaries are upper and lower quartile values, respectively)