Gauree.Malkarnekar@timesofindia.comPanaji: Researchers from the remote sensing laboratory at Goa University’s school of earth, ocean, and atmospheric sciences (SEOAS), led by professor Harilal Menon, have developed a mobile application to study how visible light decreases with depth and how underwater visibility changes in coastal and estuarine waters.The application, VEDA (visible-light extinction with depth analysis), was developed under a ₹45-lakh project funded by the naval research board of the Defence Research and Development Organisation (NRB-DRDO). The completed application has been handed over to the funding agency.Menon said the behaviour of light underwater is particularly complex in turbid coastal and estuarine waters. These waters contain varying amounts of suspended sediments, phytoplankton, and dissolved organic matter, which absorb and scatter light differently. Their concentrations also change with monsoon rainfall, river discharge, tides, and local environmental conditions. Therefore, light does not penetrate to the same depth at every location or during every season, he said.VEDA addresses this problem by combining field measurements with scientific calculations. It provides location and date specific information on how rapidly light decreases with depth and the resulting underwater visibility. User-Laboratory can select a sampling station and date to examine the corresponding optical and environmental conditions.“Light attenuation in turbid coastal waters cannot be represented accurately using a single value for all locations and seasons. VEDA shows how the underwater light profile varies with location, season, tidal conditions and water turbidity,” said oceanographer Menon.The application contains observations from 22 locations across the Zuari estuary and adjoining coastal waters of Goa. Field measurements were collected between Sept 2019 and Jan 2023, covering pre-monsoon, monsoon, and post-monsoon conditions.The depth profiles generated through VEDA are also useful for improving numerical ocean models for naval and defense applications.The researchers said measurements covering different locations, seasons, and turbidity conditions can help models represent the underwater light field more realistically. This is important because the depth at which sunlight is absorbed affects water heating, photosynthesis, phytoplankton growth, and other physical and biogeochemical processes.“By providing observed light profiles under different environmental conditions, VEDA can support better parameterisation of the underwater light field in numerical models. This can improve simulations of solar heating and biological productivity in coastal and estuarine waters,” said Menon.The application displays the 22 sampling stations on an interactive map. For each available station and date, users can view information on light penetration, vertical visibility, water temperature, salinity, season, tidal phase and other environmental conditions. It also presents graphs showing how light, temperature and salinity vary with depth.VEDA is not presently a real-time forecasting system. It provides scientifically derived information for the locations and dates covered by the field surveys. The application establishes a baseline that can be expanded using new field measurements, additional sampling locations and real-time observations.
