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| Abstract Submission No. | ABS-2022-05-0352 |
| Title of Abstract | In situ remote sensing reflectance band ratios-based FDOM quantification in the northwestern Bay of Bengal |
| Authors | Pandi Sudarsana Rao*, D.B. Rao, N.V.H.K. Chari, Nittala S. Sarma, Sarat C. Tripathy, Aneesh A.Lotlikar, N. Anilkumar |
| Organisation | National Centre for Polar and Ocean Research |
| Address | Project Scientist B | Ocean Sciences Group ESSO - National Centre for Polar & Oc Vasco-da-Gama, Goa, India Pincode: 403804 Mobile: 9491801712 E-mail: sudarsanr1@gmail.com |
| Country | India |
| Presentation | Poster |
| Abstract | In situ remote sensing reflectance band ratios-based FDOM quantification in the northwestern Bay of Bengal Pandi Sudarsana Rao1,2*, D.B. Rao1, N.V.H.K. Chari1, Nittala S. Sarma1, Sarat C. Tripathy2, Aneesh A.Lotlikar3, N. Anil Kumar2 1Marine Chemistry Laboratory, Andhra University, Visakhapatnam, Andhra Pradesh-530003, India. 2ESSO-National Centre for Polar and Ocean Research (NCPOR), Ministry of Earth Sciences, Headland Sada, Vasco-da-Gama, Goa-403804, India. 3ESSO-Indian National Centre for Ocean Information Service (INCOIS), Ministry of Earth Sciences, Hyderabad, Telangana- 500090, India. *Corresponding Author e-mail: sudarsanr1@gmail.com Synoptic measurements by ocean colour satellites are very useful for studying the marine environment. The remote sensing reflectance (Rrs) is the most important variable measured by ocean colour satellites, and derivation of all optically active substances (OAS) depends on Rrs. Phytoplankton biomass (chlorophyll), suspended sediments and coloured dissolved organic matter (CDOM) are the major OAS that determine the upwelling radiation of seawater. An important property of CDOM is its fluorescence (FDOM), and since fluorescence measurement is nearly a thousand times more sensitive than absorbance measurement, modelling fluorescence against Rrs is an attractive proposition. This exercise is expected to give more precise estimates of CDOM and be particularly helpful in low as well as high CDOM waters in which the degree of variation is small and is often poorly captured by the regular spectrophotometric measurements. This work deals with the bio-optical characteristics of the northwestern Bay of Bengal coastal waters measured from April 2014 to March 2017 (4 years). The in situ Rrs was measured using a hyperspectral underwater radiometer. The CDOM absorbance and FDOM excitation-emission matrix (EEM) spectra were also measured by UV-Visible spectrophotometer and spectrofluorometer, respectively. Through the parallel factor (PARAFAC) analysis of EEM spectra six fluorescent components consisting of four, humic-like fluorophores i.e., (Marine humic (M), UV humic-like (A), Red shifted UV humic(Ar), Visible humic-like (C), and two protein-like i.e., (Tryptophan (T) and Tyrosine (B) could be obtained. The increasing abundance of fluorophores during the study was B(0.0038)>T(0.00229)> A(0.00148)>Ar(0.00073)> M(0.00044)> C(0.00007), which infers influx of protein-rich organic matter from the terrestrial source such as from GosthaniRiver and Megadrigadda reservoir. The humic fluorophores, A and C showed significant linear relationships (R2=0.50, 0.30, 0.28, n=62 p<0.0001) with Rrs(443)/Rrs(555) and showed a moderately significant relationship with Rrs(412)/Rrs(443)(R2=0.26, 0.30,0.33 n=62, p<0.0001) whereas, the protein fluorophore T and B and humic fluorophore were did not show any relationship with the Rrs band ratios. The decreasing of R2 from M to C with Rrs(443)/Rrs(555) indicates autochthonous organic matter and increasing R2 from M to C with Rrs(412)/Rrs(443)suggests allochthonous organic matter. This study proves that the band ratios Rrs(412)/Rrs(443) and Rrs(443)/Rrs(555)can be used as proxies for deriving FDOMfrom Rrs and also identifying their sources. To the best of our knowledge, this is the first of its kind observation carried out in the coastal waters of India and it has implications for retrieval of FDOM from space-based sensors. Keywords: Bay of Bengal, Fluorescence dissolved organic matter, parallel factor analysis, 3D EEM spectra, remote sensing |