Estimating wide range Total Suspended Solids concentrations from MODIS 250-m imageries: An improved method

The objective of this study was to evaluate the performance of moderate resolution imaging spectroradiometer (MODIS) 250 m based TSS (Total Suspended Solids) retrieval model for developing the model of wide-range TSS concentrations. Using field spectral and TSS data (5.8–577.2 mg/l) collected from estuary and coast of China, we calibrated (N = 40) and validated (N = 20) the 6 TSS retrieval models in forms of single band (B1 or B2), difference of the two bands, sediment index, band ratio and log-ratio by the least-squares technique. Results showed that the quadratic model of log-ratio is of the best accuracy (Calibration: R2 = 0.752, N = 40. Validation: TSS > 31 mg/l, RMSE = 37.9 mg/l, N = 12; TSS⩽31mg/l, RMSE = 3.25 mg/l, N = 8). We also found that the spectral log-ratio values increased with the increasing of TSS when TSS < 31 mg/l, but decreased with increasing TSS when TSS > 31 mg/l. The findings of quadratic curve vertex (log-ratio: ∼1.58) in the proposed TSS model indicated that the spectral log-ratio may be sensitive to TSS of both low and high concentrations. We further applied the preferred model to retrieve TSS concentration from the MODIS 250-m images in turbid estuarial and clear coastal waters, and obtained a good mapping accuracy from the result (TSS > 31 mg/l: RMSE = 38.6 mg/l, MRE = 24.7%, N = 17; TSS⩽31mg/l: RMSE = 2.1 mg/l, MRE = 19.5%, N = 11). The vertex-based methodology of TSS model developed in the study is applicable in mapping TSS concentrations that are of a wide range variation in estuarine and coastal water bodies based on MODIS 250-m image, and as well to maximize its application potential due to high imaging frequency (two times during daytime) and appropriate space resolution of MODIS images. Therefore, the method can be used to detect the high temporal variability of TSS during tidal cycle. As such, the application of MODIS-water quality detection technology can be extended to coastal sediment movement.