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Light absorption by phytoplankton in the southern Baltic and Pomeranian lakes: mathematical expressions for remote sensing applications

Meler J., Ostrowska M., Ficek D., Zdun A.

Oceanologia

2017

No. 59 (3)

195--212

The absorption properties of phytoplankton in surface waters of the Baltic Sea and coastal lakes are examined in the context of their relationships with the concentration of the main photosynthetic pigment, chlorophyll a. The analysis covers 425 sets of spectra of light absorption coefficients aph (λ) and chlorophyll a concentrations Chla measured in 2006–2009 in various waters of the Baltic Sea (open and coastal waters, the Gulf of Gdańsk and the Pomeranian Bay, river mouths and the Szczecin Lagoon), as well as in three lakes in Pomerania, Poland (Obłęskie, Łebsko and Chotkowskie). In these waters the specific (i.e. normalized with respect to Chla) light absorption coefficient of phytoplankton aph*(λ) varies over wide ranges, which differ according to wavelength. For example, aph*(440) takes values from 0.014 to 0.124 mg−1 m2, but aph*(675) from 0.008 to 0.067 mg−1 m2, whereby Chla ranges from 0.8 to 120 mg m−3. From this analysis a mathematical description has been produced of the specific light absorption coefficient of phytoplankton aph*(λ), based on which the dynamics of its variability in these waters and the absorption spectra in the 400–700 nm interval can be reconstructed with a low level of uncertainty (arithmetic statistical error: 4.09–10.21%, systematic error: 29.63–51.37%). The relationships derived here are applicable in local remote sensing algorithms used for monitoring the Baltic Sea and coastal lakes and can substantially improve the accuracy of the remotely determined optical and biogeochemical characteristics of these waters.

Inherent optical properties and remote sensing reflectance of Pomeranian lakes (Poland)

Ficek D., Meler J., Zapadka T., Woźniak B., Dera J.

Oceanologia

2012

No. 54 (4)

611-630

This paper describes the results of comprehensive empirical studies of the inherent optical properties (IOPs), the remote sensing reflectance Rrs(λ) and the contents of the principal optically active components (OAC) i.e. coloured dissolved organic matter (CDOM), suspended particulate matter (SPM) and chlorophyll a, in the waters of 15 lakes in Polish Pomerania in 2007-2010. It presents numerous spectra of the total absorption a(λ) and scattering b(λ = bp(λ) of light in the visible band (400-700 nm) for surface waters, and separately, spectra of absorption by CDOM aCDOM(λ) and spectra of the mass-specific coefficients of absorption ap*(SPM)(λ) and scattering bp*(SPM)(λ) by SPM. The properties of these lake waters are highly diverse, but all of them can be classified as Case 2 waters (according to the optical classification by Morel & Prieur 1977) and they all have a relatively high OAC content. The lakes were conventionally divided into three types: Type I lakes have the lowest OAC concentrations (chlorophyll concentration Ca = (8.76 š 7.4) mg m-3 and CDOM absorption coefficients aCDOM(440) = (0.57 š 0.22) m-1 (i.e. mean and standard deviation), and optical properties (including spectra of Rrs(?) resembling those of Baltic waters. Type II waters have exceptionally high contents of CDOM (aCDOM(440) = (15.37 š 1.54) m-1), and hence appear brown in daylight and have very low reflectances Rrs(?) (of the order of 0.001 sr-1). Type III waters are highly eutrophic and contain large amounts of suspended matter, including phytoplankton ((CSPM = (47.0 š 39.4) g m-3, Ca = (86.6 š 61.5) mg m-3; aCDOM(440) = (2.77 š 0.86) m-1). Hence the reflectances Rrs(?) of these type of waters are on average one order of magnitude higher than those of the other natural waters, reaching maximum values of 0.03 sr-1 in ? bands 560-580 nm and 690-720 nm (see Ficek et al. 2011). The article provides a number of empirical formulas approximating the relationships between the properties of these lake waters.