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Novel work onSeasonal sediment plumes in the Krishna-Godavari basin using satellite observations

Pearl River Delta (PRD) is the third largest and one of the most productive Deltas in south China, where long-term monitoring and its assessment of water quality are necessary to understand the distribution patterns to infer the coastal zone management. The studies on long-term monitoring in water quality variable concerning the changing climate and anthropogenic effects can be made possible by continuous coverage of Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. This study attempts to study the long-term trends, quantitative measurements, and assessment of water quality variables including total suspended solids (TSS), diffuse attenuation coefficient for downwelling irradiance at 490 nm (Kd (490)), and sea surface temperature (SST) using 8-day composite and monthly data products of MODIS data for the period between July 2002 and August 2018 in the turbid waters of the PRD. Monthly products are used to quantify the variability of these water quality properties on long-term climatology, seasonal and as well as spatial distributions to interannual timescales. We observed a decreasing trend of TSS and Kd (490) between 2002 and 2018, though not significant, whereas, an increasing trend of SST has recorded for the PRD region during the same time. Seasonal patterns of TSS, Kd (490) and SST showed significant differences between the seasons. The high values of TSS (>15 gm−3) and Kd (490) (>2 m−1) were found in summer, autumn followed by winter, and low values (

Mesoscale phenomena are highly energetic features of ocean dynamics and circulation patterns. Their influence on biological and biogeochemical processes varies widely from advective transport and also from the generation of variations in the environment that affect biological and chemical rates. This study investigates the surface chlorophyll-a (Chl-a) bloom affect in the case-1 (open ocean) waters of Arabian Sea off the southwest coast of India in response to the cold core eddy in the post-monsoon 2016 using satellite-based observations. The 8-day composite of Chlorophyll-a (Chl-a), Sea Surface Height Anomalies (SSHA), Sea Surface Temperature (SST) and the wind field vectors were analyzed to study the Chl-a bloom characteristics and eddy mechanism. The results show that a very high concentration of Chl-a (6 mg/m-3) bloom occurred during the cold-core eddy formation which lasted for more than a month. Analysis revealed that the Chl-a bloom is attributed to the combined effect of surface and subsurface processes such as cyclonic structure of cold-core eddy, high Ekman pumping velocity, negative values SSHA, decreased values of SST, and nutrient injection from subsurface to the surface. Our study concluded that the presence of pre-existing cyclonic cold-core eddy, decreased SST and high Ekman pumping velocity played a major role in the formation of Chl-a bloom in the study area.

The Geostationary Ocean Color Imager (GOCI) sensor, with high temporal and spatial resolution (eight images per day at an interval of 1 hour, 500 m), is the world’s first geostationary ocean color satellite sensor. GOCI provides good data for ocean color remote sensing in the Western Pacific, among the most turbid waters in the world. However, GOCI has no shortwave infrared (SWIR) bands making atmospheric correction (AC) challenging in highly turbid coastal regions. In this paper, we have developed a new AC algorithm for GOCI in turbid coastal waters by using quasi-synchronous Visible Infrared Imaging Radiometer Suite (VIIRS) data. This new algorithm estimates and removes the aerosol scattering reflectance according to the contributing aerosol models and the aerosol optical thickness estimated by VIIRS’s near-infrared (NIR) and SWIR bands. Comparisons with other AC algorithms showed that the new algorithm provides a simple, effective, AC approach for GOCI to obtain reasonable results in highly turbid coastal waters.

Red Sea is one of the world's major strategic shipping routes for crude oil transportation. Accidental spills of crude oil into the environmentally sensitive marine environments are known to impact the marine life. However, studies on direct assessment of oil spill on marine ecosystem, in particular on the primary productivity and bio-optical parameters in the Red Sea waters were poorly constrained owing to lack of sustained observations. Thus, in this study, an attempt has been made to use high spatial and temporal resolution of Moderate Resolution Imaging Spectroradiometer (MODIS) observations to monitor the oil spill explosion occurred on October 11, 2019, and its impact on the chlorophyll -a (Chl-a) concentrations. We noticed a significant increase in concentrations of Chl-a on the following day of oil spill. These changes are accounted for and are influenced by hydrocarbons along the track of oil spill. Our findings suggest that both wind speed and high Ekman pumping velocity support the upwelling of nutrient-rich water from subsurface, which facilitated the growth of phytoplankton and thus the high Chl-a in the oil spill areas.