Development of Nitrate Algorithm for the Southwest Bay of Bengal Water and Its Implication Using Remote Sensing Satellite Datasets

The in situ sampled and analyzed nitrate, chlorophyll and sea surface temperature (SST) during the period 2009-2010 from monthly coastal stations and cruise datasets have been interpreted for the southwest Bay of Bengal water to develop nitrate algorithm for remote sensing applications in ocean biogeochemical cycling. The monthly sampled data points were retrieved from the coastal water around Pondicherry, Cuddalore, Parangipettai and Nagapattinam along Tamil Nadu coast, India. The cruise data has been retrieved between the coastal and offshore water along the Chennai and Kakinada (AP) segment. The SST and chlorophyll datasets has been regressed with the nitrate three dimensionally with 105 in situ data points. Parabolic function has been fitted, producing significant relationship. During the following seasons: summer (April-June), pre-monsoon (July-September), monsoon (October-December) and post-monsoon (January-March) the coefficient of determination R
²
value found to be 0.16, 0.34, 0.48 and 0.56 respectively. The satellite derived nitrate map has been generated for February 28, 2010 using Oceansat-2 OCM derived chlorophyll concentration and MODIS-Aqua derived SST basing on in situ modeled nitrate algorithm. The satellite derived nitrate concentration range has been observed to be 0.01 to 12.0 μg/L with high nitrate fronts off Tamil Nadu and Kerala coast around southern Indian tip. High nitrate and low chlorophyll (HNLC) condition has been of concern, where SST was high. Similar contrasting features in SST and nitrate images have been observed. The developed algorithm has been validated for a different dataset of March 16 and 18, 2010 and R
²
value found to be 0.508 and the algorithm observed to be working satisfactory over the southwest Bay of Bengal region.