Regional algorithms for calculating the chlorophyll concentration in the Baltic Sea have been developed

in several papers, in particular by specialists from the Institute of Oceanology, Polish Academy of Sciences (Darecki & Stramski 2004, Darecki et al. 2008, Woźniak et al. 2008). The applicability of these algorithms for determining Chl concentration in the Gulf H 89 cost of Finland was tested with our field data; the results are discussed in section 4.1. We derived several algorithms in different forms specifically for the Gulf of Finland. After various tests, the input parameter was selected as X = log[Rrs(547)/Rrs(531)], where 547 and 531 nm are the effective wavelengths of the MODIS-Aqua spectral bands (see section 4.3). The regression equations were derived as Chl vs. X and log Chl vs. X with formulae of the first- and second-order: this website #1 Chl = 183X – 7.73; Algorithms #1, #5 (n = 15) and #2, #6 (n = 25) were derived by using data from the expeditions of 2012 and 2013 respectively. The equations for these years differ clearly from each other,

but Student’s test shows that the differences between the regression coefficients of equations #1 and #2, #5 and #6 are not statistically significant in both cases. Equations #3, #4 and #7, #8 were derived for the combined data set (n = 40). The evaluation parameters for the above algorithms are given in Table 1; Figures 5 and 6 show the results in graphical form. The standard errors for algorithms #4 and #8 are equal to 3.26 mg m−3 and 3.37 mg m−3respectively; as seen from Figure 6, both algorithms

mostly overestimate Chl values < 5 mg m−3, but algorithm #8 does so to a lesser degree than algorithm #4. It is also seen that both algorithms underestimate Chl values < 5 mg DNA ligase m−3, but algorithm #4 to a lesser degree than algorithm #8. As a result, algorithm #8 underestimates the average value of Chl (about 13%), but the average value of the ratio of Chlcalc/Chlmeas for this algorithm is ~ 1.14; in the case of algorithm #4 the calculated average value of Chl is practically equal to the measured one, but the ratio of Chlcalc/Chlmeas is 1.30. Since most of the waters in the study area have chlorophyll concentrations < 5 mg m−3, algorithm #8 was selected as the primary one. Figure 7 shows the spatial distribution of the chlorophyll concentrations calculated from MODIS-Aqua data on 22 July 2012 and 27 July 2013 using the selected algorithm. The maps show no basic differences between the chlorophyll concentration distributions in 2012 and 2013. Most of the study area is occupied by water with chlorophyll concentrations of 2–5 mg m−3, but there are heterogeneities within this gradation which may be > 5 and even 10 mg m−3 as well as lower values. The highest chlorophyll concentrations are recorded in the eastern part of the Gulf of Finland near Neva Bay and along the southern coast of the Gulf (especially in 2012).