148(Rrs(490)/Rrs(555))−2.18.POC=0.148Rrs490/Rrs555−2.18. This particular formula may be compared with the formula presented in the previously cited paper by Stramski et al. (2008) on relationships between POC and optical properties in the eastern South Pacific and eastern Atlantic Oceans. The authors of that work gave two very similar variants of the POC vs. Rrs(490)/Rrs(555) relationships, one of which (relating to all the data in Stramski et al., i.e. including the Chilean

upwelling stations) took the following form: POC = 0.3083(Rrs(490)/Rrs (555))− 1.639. The latter formula is plotted in Figure 9 together with formula  (13). Such a comparison shows clearly that the formula describing LBH589 mw the average oceanic relationship has a less steep slope (compare the constants C2: − 2.18 with − 1.639). As a consequence of that within the range of minimal blue-to-green reflectance values in the analysed Baltic Sea dataset (values of about 0.4) both formulas would predict similar POC concentrations, but within the range of maximum blue-to-green values (here ca. 0.9) the POC concentrations predicted according to the oceanic formula would be about twice as high as those estimated with formula  (13).

However, while performing such a comparison it has to be borne in mind that formula  (13) does not offer very attractive values of statistical parameters: among other PFT�� things, the standard error factor X is equal to 1.74, which is much higher than the value of X of 1.56 obtained with formula  (11), which makes use of the blue-to-red ratio. With regard to formulas for estimating Chl a, the fact that no single band formula was found to be acceptable for estimating that pigment concentration for the Baltic Sea data analysed here (no such formula is presented in Table 3) is in agreement with one of the

conclusions suggested by Bukata et al. (1995), namely, that a reliable estimate of chlorophyll concentration in waters other than Case 1 (other than open ocean Clomifene regions) most likely cannot result from a single wavelength reflectance relationship. The other important fact is that among the reflectance ratio formulas found here to be acceptable for estimating the Chl a concentration in the southern Baltic Sea (see the last six lines in Table 4) there is also no formula using the classic blue-to-green ratio that would resemble any of the standard remote sensing algorithms commonly used for Case 1 waters. This is in agreement with earlier studies documenting the generally poor performance of standard Chl a satellite algorithms when they were applied to the Baltic Sea environment (see e.g. Darecki & Stramski (2004)). But it has to be pointed out that the few positive observations/arguments presented above are only qualitative in their nature.