Remote sensing monitoring of total suspended solids concentration in Jiaozhou Bay based on multi-source data

Abstract

Total suspended solids (TSS) concentration (mg/L) is a significant indicator of coastal water environments monitoring. First, quantitative retrieval models of TSS concentrations in Jiaozhou Bay (JZB) were developed based on Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) data, and the retrieved TSS concentrations in JZB from 1984 to 2021 were obtained. Then, the reliability of the retrieved TSS from Landsat and MODIS was evaluated, and the temporal and spatial variation in TSS concentration was analyzed. Finally, the main factors influencing the variation in TSS concentration in JZB were analyzed. The results show that both Landsat and MODIS retrieval models proposed in this study have good accuracies (Landsat: R2 = 0.64, RMSE = 2.09 mg/L, MAPD = 33.96%; MODIS: R2 = 0.71, RMSE = 2.54 mg/L, MAPD = 32.81%). The TSS concentration in JZB fluctuated between 1984 and 2021, showing a downward trend. The TSS concentration in JZB exhibited an obvious seasonal variation, with a higher concentration in spring and winter owing to strong winds and a lower concentration in summer and autumn. TSS decreased gradually from northwest to southeast. The average spatial variation scale of TSS monitoring in JZB was 72 m and the optimal observation time window was 10:16–12:16. Although the retrieved TSS of Landsat and MODIS were highly consistent (R2 = 0.70, RMSE = 2.09 mg/L), differences were still observed. The exponential function in the retrieval models was the main reason for the large difference between Landsat TSS and MODIS TSS in the nearshore high-value area. The different spatial resolutions, image acquisition times, and signal-to-noise ratios of Landsat and MODIS were also important reasons for the differences. Wind speed was the main factor influencing the annual, seasonal, and monthly variation in TSS concentration in JZB, while the Jiaozhou Bay Bridge only had an effect on the TSS concentration during the construction period.