Retrieval of total suspended matter concentration from Gaofen-1 Wide Field Imager (WFI) multispectral imagery with the assistance of Terra MODIS in turbid water – case in Deep Bay

This study proposed a method for developing high spatial resolution Gaofen-1 satellite (GF-1) Wide Field Imager (WFI)-based total suspended matter concentration (CTSM) retrieval model with the assistance of Moderate Resolution Imaging Spectroradiometer (MODIS) data, using the Deep Bay in China as a case. Based on long-term calibrated CTSMmeasurements of optical backscatter (OBS) 3A turbidity and temperature monitoring system of two stationary stations from January 2007 through November 2008, 33 match-ups were selected to build an exponential retrieval model for MODIS atmospherically corrected remote-sensing reflectance (Rrs) ratio (Rrs,645/Rrs,555). Validation of the MODIS model showed well agreement with the seven in situCTSMmeasurements with a root mean squared error (RMSE) of 5.06 mg l−1and a coefficient of determination R2of 0.80. Aided with six MODIS retrieved CTSMproducts, different band combinations (single band (Rrc,660), band subtraction (Rrc,660–Rrc,560), band ratio (Rrc,660/Rrc,560), and total suspended matter index at 660 nm band (TSMI660) were evaluated for simultaneous GF-1 WFI Rayleigh-corrected reflectance (Rrc). The results showed that the exponential model based on the Rayleigh-corrected reflectance ratio (Rrc,660/Rrc,560) could achieve acceptable accuracy, with RMSE of 14.80 mg l−1and R2of 0.62. The proposed method would be helpful for dynamic monitoring in the Deep Bay, and more important could also provide an alternative approach for studies when in situ measurements are unreachable.