Oceanologia (Nov 2012)
Inherent optical properties and remote sensing reflectance of Pomeranian lakes (Poland)
Abstract
This paper describes the results of comprehensive empirical studies of theinherent optical properties (IOPs), the remote sensing reflectance Rrs(λ) andthe contents of the principal optically active components (OAC) i.e. coloureddissolved organic matter (CDOM), suspended particulate matter (SPM) andchlorophyll a, in the waters of 15 lakes in Polish Pomerania in 2007-2010.It presents numerous spectra of the total absorption a(λ) andscattering b(λ) ≈ bp(λ) of light in the visibleband (400-700 nm) for surface waters, and separately, spectra of absorptionby CDOM aCDOM(λ) and spectra of the mass-specificcoefficients of absorption ap*(SPM)(λ) and scatteringbp*(SPM)(λ) by SPM. The properties of these lake waters are highly diverse, but all of them can beclassified as Case 2 waters (according to the optical classification by Morel& Prieur 1977) and they all have a relatively high OAC content. The lakeswere conventionally divided into three types: Type I lakes have the lowestOAC concentrations (chlorophyll concentration Ca = (8.76 ± 7.4) mg m-3 and CDOM absorption coefficientsaCDOM(440) = (0.57 ± 0.22) m-1 (i.e. mean and standarddeviation), and optical properties (including spectra of Rrs(λ)resembling those of Baltic waters. Type II waters have exceptionally highcontents of CDOM (aCDOM(440) = (15.37 ± 1.54) m-1),and hence appear brown in daylight and have very low reflectancesRrs(λ) (of the order of 0.001 sr-1). Type III waters arehighly eutrophic and contain large amounts of suspended matter, includingphytoplankton ((CSPM = (47.0 ± 39.4) g m-3,Ca = (86.6 ± 61.5) mg m-3; aCDOM(440) = (2.77 ± 0.86) m-1). Hence the reflectances Rrs(λ)of these type of waters are on average one order of magnitude higher thanthose of the other natural waters, reaching maximum values of 0.03 sr-1in λ bands 560-580 nm and 690-720 nm (see Ficek et al. 2011). Thearticle provides a number of empirical formulas approximating therelationships between the properties of these lake waters.
