Ocean remote sensing for spatiotemporal variability of wave energy density and littoral current velocity in the Southern Indian offshore

Abstract

Abstract Spatiotemporal variability of wave energy and littoral current velocity releasing at zones play a major role for formation of coastal landforms and environmental ecosystems in the South Indian coastal region. Impacts of wave energy and littoral current into the shore are mainly subject to several geomorphological changes by controlling natural and manmade activities and highly influencing coastal dynamics like erosion and accretion. Mathematically, the wave energy is calculated using the linear wave theory and the equation is expressed as E = 1 8 ρ g H 2 , whereas the measurement of littoral current velocity is performed by using the equation is represented as V L H = 20.7 m ( g H b ) 1 / 2 sin 2 α b . The parameters including significant wave height, seawater density (subject to salinity and temperature), gravity acceleration, wave breaker height, wave break angle, and offshore slope are used as inputs for executing the preceding equations, in which the significant wave height is estimated using gridded significant wave height level-4 products based on altimetry measurements of satellites Sentinel-3A, Sentinel-3B, Jason-3, Saral (AltiKa), Cryosat-2, and CFOSAT. The GIS modeling of the linear equation is executed using the raster layer of the preceding parameters for estimating wave energy density and littoral current velocity at 10 ∗ 10\xa0m pixel scale. The Southern Indian offshore region found the highest range of wave energy density during premonsoon (June–September) and it is estimated at 3.46–10.48\xa0kJ/m2 with a mean value of 6.52\xa0kJ/m2 due to impacts of a southwest monsoonal wind from the Indian Ocean and Arabian Sea. Similarly, the offshore region shows a higher rate of wave energy density during monsoon (October–December) at the range of 1.12–9.78 52\xa0kJ/m2 with a mean value of 6.06 52\xa0kJ/m2 due to stronger influences of northeast monsoonal wind velocity from the Bay of Bengal Sea. However, the offshore region is recorded as a lower rate of wave energy density during postmonsoon (March–May), at the range of 1.76–4.09 6.52\xa0kJ/m2 with a mean value of 3.06 6.52\xa0kJ/m2, whereas the annual average of wave energy density is estimated at 1.86–5.68\xa0kJ/m2 in coastal water of the nearshore area and 5.69–10.48\xa0kJ/m2 in the offshore water column. The spatiotemporal variability of wave energy density shows the standard deviation value at 0.4–3.24 during the three seasons of 2017–2018. Meanwhile, the combined action of wind and wave controls the flow and movement of littoral current along the Southern Indian coastal water, and it is estimated at the velocity of 0.14–0.55\xa0m/s during the three seasons. The energy releasing from wave and littoral current to the shoreline results in the morphodynamics of landforms at various locations along the Southern Indian coastal stretch, whereas some coastal zones found erosion landforms while experiencing the higher wave energy but lower velocity of littoral current due to backwashing of sediments. Meanwhile, the reversing processes in specific spots formed as depositional landforms due to swashing of sediments. Long-term monitoring of wave energy and littoral current can be possible through ocean remote sensing, and it provides vital information for oceanographic studies and making plans for sustainable coastal zone management.