Total Suspended Matter Distribution in the Hooghly River Estuary and the Sundarbans: A Remote Sensing Approach

Monitoring of total suspended matter (TSM) concentration in the coastal waters is vital for water quality monitoring and coastal management. In this study, TSM over the highly dynamic Hooghly estuary region is derived using moderate resolution imaging spectroradiometer (MODIS) surface reflectances at 645 nm and
in situ
TSM observations. MODIS TSM products show a correlation of 0.95, root-mean-square error of 24.72 g/m
³
, and mean absolute and percentage errors of 18.25 g/m
³
and 23.2%, respectively, when compared with
in situ
measurements. Subsequently, TSM variability in the Hooghly estuary from the derived TSM maps was analyzed during the period 2003–2018 on monthly and seasonal time scales. The annual cycle of TSM showed peak concentration (>250 g/m
³
) during the southwest monsoon season that could be attributed to large-scale river discharge as compared with the northeast and intermonsoon seasons (∼100–150 g/m
³
). Interannual variability showed higher TSM during the years 2004, 2012, and 2013 and low during 2005 and 2015. It could be concluded that the fine tuning of the existing TSM retrieval algorithm is essential based on the long-term earth observation data for monitoring the sediment distribution in the coastal and estuarine regions utilizing available satellite observations, particularly in the highly turbid estuaries, such as the Hooghly estuary.