Validation of Chlorophyll-a concentrations in the Estuarine Waters of Bay of Bengal using OCM-2 Data : A case study in the Godavari basin

T. Preethi Latha, P.V.Nagamani, K.H.Rao, S.K.Dash, S.B.Choudhury, Aziz Rehman, V.V.S.S.Sarma 1National Remote Sensing Center, ISRO, Hyderabad 2-National Institute of Oceanography-RC, CSIR, Visakhapatnam 3-Integrated Coastal and Marine Area Management, Chennai Abstract Chlorophyll measurements were made on a coastal cruise during March 2012 in the estuarine waters of Bay of Bengal in Godavari basin along Off Kakinada and Yanam coast. In-situ optical data were collected at 21 stations (surface to 150m) using Underwater radiometer (Hyperpro-II). In-vivo chlorophyll data were collected using wet labs fluorometer integrated with underwater Hyperspectral radiometer. Apart from this chlorophyll-a concentrations were measured using HPLC by collecting the water samples at each sampling location. And also chlorophyll-a concentrations were estimated from the OCM-2 satellite data, processed using global SeaWiFS Data Analysis System (SeaDAS) software v.6.2 with the existing global ocean colour algorithms namely, OC2 and OC4V4. At all the 21 stations 33 samples collected for chlorophyll-a estimation, however, surface water samples of all the stations only being used for direct comparison among chlorophyll concentrations of HPLC, in-situ (fluorometrically measured with Hyperpro-II) chlorophyll-a with satellite derived chlorophyll from OCM-2. A good correlation between the fluorormeter derived and HPLC measured chlorophyll-a concentration with an R value of 0.78 was observed. The relation between Chlorophyll-a concentration measured from HPLC and retrieved from OCM-2 (OC2 and OC4V4 algorithms) using SeaDASv.6.2 for 10 samples has been compared for validation and obtained an R value of 0.6. Also comparisons done with the in-situ measured (fluorometer) Chlorophyll-a concentration with OCM-2 chlorophyll data (OC4 -V4 and OC2 algorithms) and validation with 10 concurrent in-situ surface measurements showed a significant overestimation by OCM-2 at low chlorophyll-a concentrations and underestimation at high chlorophylla concentrations.