Abstract
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/m3, and mean absolute and percentage errors of 18.25 g/m3 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/m3) 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/m3). 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.
Highlights
Monitoring and assessment of suspended sediments is pursued across different estuaries and coastal regions of the world using in-situ observations
TSM retrieval algorithm was developed based on Moderate resolution Imaging Spectroradiometer (MODIS) single band reflectance in the red region (λ = 645nm) and the available in-situ observations through regression based best-curve fit method and is given as follows: TSM = a ∗ eb∗ref where, TSM is the total suspended matter concentration in g/m3, ref is the surface reflectance (Reflectance units), a and b are the calibration coefficients
The final, recalibrated algorithm showed Root Mean Square Error (RMSE) of 24.72 g/m3, correlation coefficient (R) of 0.95 with Mean Absolute Error (MAE) of 18.25 g/m3 and Mean Percentage Error (MPE) of 23.2 % when compared with the insitu data
Summary
Monitoring and assessment of suspended sediments is pursued across different estuaries and coastal regions of the world using in-situ observations. In-situ data-based approaches are insufficient to estimate the complex dynamics of suspended sediments owing to their limited spatial and temporal coverage. Satellite remote sensing observations cannot entirely replace in-situ measurements, they provide an alternate and effective means for monitoring the distribution of total suspended matter (TSM) at multi spatial and temporal scales. This is not feasible with the traditional observational sediment sampling techniques and in-situ measurements [1], [2]. An integration of satellite-derived products with insitu observations has enabled researchers to generate a wealth of data in the coastal and estuarine waters in the recent years, thereby resulting in a more effective analysis of the suspended sediment dynamics in regional waters
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