Parameterization of Spectral Particulate and Phytoplankton Absorption Coefficients in Sognefjord and Trondheimsfjord, Two Contrasting Norwegian Fjord Ecosystems

Veloisa Mascarenhas,Oliver Zielinski

doi:10.3390/rs10060977

Veloisa Mascarenhas, Oliver Zielinski

Open Access

https://doi.org/10.3390/rs10060977

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Journal: Remote sensing	Publication Date: Jun 20, 2018
Citations: 4	License type: CC BY 4.0

Affiliation: Carl von Ossietzky University of Oldenburg

Abstract

We present here parameterizations of particulate and phytoplankton absorption coefficients as functions of pigment concentrations (Tchla) in Sognefjord and Trondheimsfjord along the northwestern coast of Norway. The total particulate and non-algal optical densities were measured via quantitative filter technique (QFT) in a spectrophotometer with integrating sphere. The spectral parameter coefficients A(λ) and E(λ) of the power law describing variations of particulate and phytoplankton absorption coefficients as a function of Tchla, were not only different from those provided for open ocean case 1 waters, but also exhibited differences in the two fjords under investigation. Considering the influence of glacial meltwater leading to increased inorganic sediment load in Sognefjord we investigate differences in two different parameterizations, developed by excluding and including inner Sognefjord stations. Tchla are modelled to test the parameterizations and validated against data from the same cruise and that from a repeated campaign. Being less influenced by non-algal particles parameterizations performed well in Trondheimsfjord and yielded high coefficients of determination (R2) of modelled vs. measured Tchla. In Sognefjord, the modelled vs. measured Tchla resulted in better R2 with parameter coefficients developed excluding the inner-fjord stations influenced by glacial meltwater influx.

Highlights

The inherent optical properties (IOPs), i.e., the absorption a (λ) and back scattering bb (λ) coefficients of the optically active constituents (OACs) govern the diffuse reflectance Rrs (λ) above water, through a relationship of the form, Rrs (λ) = F bb ( λ )a ( λ ) + bb ( λ ) (1)established via studies of radiative transfer [1]
Bio-optical models developed for predicting underwater light field or interpreting ocean color imageries require the bulk IOPs to be expressed in terms of contributions of individual OACs as functions of their content in seawater, represented in Equation (2): a(λ) = aw (λ) + a p (λ) + acdom (λ)
The near-surface concentrations of OACs and absorption coefficients along transects in Sognefjord and Trondheimsfjord are illustrated in Figure 2, respectively

Summary

Introduction

Bio-optical models developed for predicting underwater light field or interpreting ocean color imageries require the bulk IOPs to be expressed in terms of contributions of individual OACs as functions of their content in seawater, represented in Equation (2): a(λ) = aw (λ) + a p (λ) + acdom (λ). The total particulate absorption spectrum, influenced by phytoplankton pigments, aphy (λ) and non-algal particles (NAP), anap (λ) is represented as, a p (λ) = a phy (λ) + anap (λ) (3). Absorption by non-algal particles is reported to have a spectral shape similar to CDOM, decreasing exponentially with increase in wavelength. Phytoplankton absorption spectra exhibit more variability both in magnitude and spectral characteristics, being influenced by factors such as pigment composition, light levels, cell size, and package effects [5]

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