Abstract. Studies on suspended sediment concentrations at a
seasonal scale play a vital role in understanding coastal hydrodynamic
processes in an area. Assessment of spatio-temporal changes in suspended
sediments in nearshore areas has gained complexity due to the utilization of
conventional methods; this issue can be successfully
solved nowadays using multi-temporal remotely sensed images with the help of
advanced image processing techniques. The present study is an attempt to
demonstrate the model algorithm used to extract suspended sediment
concentrations using Landsat 8 OLI (Operational Land Imager) sensor images.
The study was executed in a near-offshore area of the Thiruvananthapuram
coast, southern India, and focused on the extraction of suspended sediment
concentrations and their seasonal variability during pre-monsoon and
post-monsoon periods. The OLI images were pre-processed to obtain the actual
reflectance using the FLASSH module of the ENVI v5.5 software. The generic
model developed herein is designed to compute the spectral reflectance
variability between coastal water and suspended sediments and to
differentiate the spatial accumulation of the suspended sediment
concentrations from the coastal water at the pixel scale. Maximum (0.8 % in
near-infrared bands) and minimum (0.6 % in blue bands) spectral reflectance
indicates the occurrence of suspended sediments in the coastal water. The
model-derived results revealed that the suspended sediment concentration
gradually decreased with increasing depth and distance from the shoreline.
Higher sediment concentrations accumulated at lower depths in coastal water
due to wave and current action that seasonally circulated the sediments. This
higher concentration of the suspended sediment load was estimated to be
0.92 mg L−1 at the shallow depths (<10 m) of the coastal waters and
0.30 mg L−1 at a depth of 30 m. Seasonal variability of suspended
sediments was observed in a north–south direction during the pre-monsoon;
the reverse was noted during the post-monsoon period. The spatial variability
of suspended sediments was indirectly proportional to the depth and distance
from the shoreline, and directly proportional to offshore wave and littoral
current activity. This study proves that the developed model coupled with the
provided computational algorithm can be used as an effective tool for the
estimation of suspended sediment concentrations using multi-temporal OLI
images; furthermore, the output may be helpful for coastal zone management
and conservation planning and development.
Temperature estimates of lower Miocene (Burdigalian) coastal water of Southern India using a revised otolith ‘clumped’ isotope palaeothermometer
