Fig. 1. Locations of 14 SSC field measurements on March 27（blue），May 24（brown）and 31 October（black）2019 near the Yangtze estuarine and coastal waters. The stars and diamonds represent the field measurements collected by the buoy stations and ships，respectively

Fig. 2. Flow diagram for the entire SSC retrieval process.

Fig. 3. Line chart of total in situ SSC data. The number 1~7，8~10，11~14 samples were measured on 31 October，24 May and 27 March 2019，separately. A separation line（purple）is plotted to highlight the water samples 1~7 used for the final retrieval. The blue to yellow colors of dots intuitively show the low to high SSC levels. The lines drew in blue and orange represent the origin SSC values of all 3 days and sorted SSC values of 31 October 2019，respectively

Fig. 4. Spectra of the surface reflectance in the research region on 27 March （a） 24 May （b） and 31 October （c） 2019. The dotted，dashed and solid lines represent the low，middle and high SSC values，respectively （d） some surface reflectance spectra extracted from different typical ground objects on 31 October 2019

Fig. 5. The 7 examples of preprocessed surface reflectance spectra for different SSCs measured on 31 October 2019

Fig. 6. The relationships between the regularization hyperparameter λ，RMSE，MAPE and R² for D’Sa （a） Nechad （b） Ruhl （c） and Loisel （d） models in the application for baseline model calibration

Fig. 7. The scatter diagrams （left） between the predicted values and field measurement values and the NNC calibration curves （right） for D’Sa （a），Nechad （b），Ruhl（c） and Loisel（d） models in the application for baseline model calibration

Fig. 8. The scatter diagrams （left） between the predicted values and field measurement values and the NNC calibration curves （right） for D’Sa （a），Nechad （b），Ruhl （c） and Loisel （d） models in the application for temporal calibration

Fig. 9. SSC retrieval results of the baseline model （a） and NNC double calibration （b） using the D’Sa model in the application of temporal calibration based on the GF-5 images in the Yangtze estuarine and coastal waters on 31 October 2019. For result comparison，the magnified images of the region of interest（ROI）labelled in the red area are provided in the top left of each picture. The green star and pink diamond denote the samples with 0.14 and 0.63 g/L SSC values，respectively

Table 1. Main parameters for GF-5 AHSI

Table 2. Comparison between baseline and NNC results in the application for baseline model calibration.

Table 3. Comparison between baseline and NNC results in the application for temporal calibration