Comparison of hyperspectral measurements of the attenuation and scattering coefficients spectra with modeling results in the north-eastern Baltic Sea

摘要

The spectral variations in the attenuation and scattering coefficients measured with a hyperspectral ac-spectra (Wetlabs) instrument were analyzed from a dataset collected in the vicinity of commercial harbors on the Estonian coast of the Gulf of Finland, Baltic Sea. In total, the measured TSM concentration varied from 0.4 to 30 mg L-1 and the concentration of Chl a varied from values below the detection limit (0.05) to 23 mg m(-3). The reliability of the power law describing the particle attenuation c(p) (lambda) and scattering b(p)(lambda) coefficients was evaluated by means of a determination coefficient (R-2). The power law described the particle attenuation spectra with high accuracy (R-2 > 0.67), giving the dataset an average c(p) (lambda) slope of 1.3. In the case of particle scattering coefficients, the power law did not represent the whole dataset. Depending on a particular spectrum, the R-2 varied from 0 to 1.0 and the slope varied from 1.15 to -0.56. Decomposition of b(p)(lambda) into dominant modes using principal component analyses resulted in the first principal mode accounting for the power law dependence of b(p)(lambda), i.e. the "mineral-type" spectrum, and the second and third mode representing the characteristic b(p)(lambda) of dominant algal particles, i.e. the "algae-type" spectrum. From our dataset we estimated that if Chl a concentration is above 10 mg m(-3) or below 5 mg m(-3) then most likely the "algae-type" or the "mineral-type" spectrum is dominant, respectively. There was strong linear relationship (R-2 > 0.92) between TSM concentration and c(p)(555) and b(p)(555),irrespective of the dominant shape of the particle scattering spectra. The estimated TSM-specific attenuation and scattering coefficients at 555 nm were 0.8 m(2) g(-1) and 0.68 m(2) g(-1), respectively. Corresponding values for water samples with a dominant "mineral-type" spectrum were 0.85 m(2) g(-1) and 0.73 m(2) g(-1), respectively and for water samples with a dominant "algae-type" spectrum were 0.64 m(2) g(-1) and 0.52 m(2) g(-1), respectively. (C) 2015 The Authors. Published by Elsevier Ltd.