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Performance evaluation of non-water absorption coefficient partitioning algorithms in optically complex coastal waters of Kochi and Goa, India

Kolluru Srinivas, Gedam Shirishkumar S., Inamdar Arun B.

Oceanologia

2021

No. 63 (4)

420--437

Absorption coefficient partitioning algorithms (APAs) were developed to partition the total absorption coefficient (a(λ)) or total non-water absorption coefficient (anw(λ)) into the absorption subcomponents, i.e., absorption due to phytoplankton aph(λ), colored dissolved organic matter (CDOM) aƍ(λ) and non-algal particulate matter ad(λ), λ is the wavelength. Absorption coefficients of CDOM and non-algal particulate matter are generally combined due to a similarity in exhibited spectral shape and represented as colored detrital matter (CDM) absorption coefficient, adƍ(λ). This study focuses on the applicability of five APAs Schofield's, Lin's, Zhang's, Stacked Constraints Model (SCM) and Generalized Stacked Constraints Model (GSCM), in deriving the absorption subcomponents from anw(λ) in optically complex coastal waters of Kochi and Goa, India. The average spectral Mean Absolute Percentage Errors (MAPE) obtained for all models in the retrieval of aph(λ), ad(λ), aƍ(λ) and adƍ(λ) lie in the ranges of 26-44%, 37-45%, 34-65% and 42-56%. Slopes of adƍ(λ), aƍ(λ) and ad(λ) as indicated by Sdƍ, Sƍ and Sd are derivable from GSCM, Schofield and Lin's models only. GSCM model exhibited good retrieval capability of Sd with MAPE values of 22% and a correlation coefficient of 0.74. In retrieval of Sƍ parameter, none of the models demonstrated satisfactory performance. Overall, the GSCM and Schofield's models demonstrated good performance in the retrieval of absorption subcomponents, aph(λ), adƍ(λ), ad(λ) and Sd. Effect of applying baseline correction to ad(λ) on model performance is studied. Tuning with in situ data can further improve the absorption subcomponent and slope parameter retrieval capability of the models.

Bio-optical trends of seas around Turkey : An assessment of the spatial and temporal variability

Bengil F., Mavruk S.

Oceanologia

2018

No. 60 (4)

488--499

Until present, bio-optical characteristics and their variations in the eastern Mediterranean and Black Sea have rarely been studied. In order to characterize the basic features of bio-optical variables found in the seas surrounding Turkey, remotely sensed data sets covering the period between September 1997 and March 2017 were studied for the purpose of this research. Chlorophyll-a concentration (CHL), absorption coefficient by colored dissolved organic matter (CDOM) and particulate backscattering coefficient (BBP) were both evaluated to describe their recent linear and non-linear inter-annual patterns in the sub regions of the northern Levantine Sea (LS), the eastern Aegean Sea (AS), the Marmara Sea (MS) and the southern Black Sea (BS). The results determined a highly significant and decreasing trend of CHL in the Black Sea, whilst most other regions from the seas around Turkey displayed non-significant trends. The analysis indicated that the seas around Turkey can be clustered into two regions based on their bio-optical properties; one being the Black Sea and Marmara Sea, and the second cluster being the Aegean Sea and Levantine Sea.