Inherent Optical Properties of the Baltic Sea in Comparison to Other Seas and Oceans

Abstract

In order to retrieve geophysical satellite products in coastal waters with high coloured dissolved organic matter (CDOM), models and processors require parameterization with regional specific inherent optical properties (sIOPs). The sIOPs of the Baltic Sea were evaluated and compared to a global NOMAD/COLORS Reference Data Set (RDS), covering a wide range of optical provinces. Ternary plots of relative absorption at 442 nm showed CDOM dominance over phytoplankton and non-algal particle absorption (NAP). At 670 nm, the distribution of Baltic measurements was not different from case 1 waters and the retrieval of Chl a was shown to be improved by red-ratio algorithms. For correct retrieval of CDOM from Medium Resolution Imaging Spectrometer (MERIS) data, a different CDOM slope over the Baltic region is required. The CDOM absorption slope, S CDOM , was significantly higher in the northwestern Baltic Sea: 0.018 (±0.002) compared to 0.016 (±0.005) for the RDS. Chl a-specific absorption and a d [SPM] *(442) and its spectral slope did not differ significantly. The comparison to the MERIS Reference Model Document (RMD) showed that the S NAP slope was generally much higher (0.011 ± 0.003) than in the RMD (0.0072 ± 0.00108), and that the SPM scattering slope was also higher (0.547 ± 0.188) vs. 0.4. The SPM-specific scattering was much higher (1.016 ± 0.326 m 2 g −1) vs. 0.578 m 2 g −1 in RMD. SPM retrieval could be improved by applying the local specific scattering. A novel method was implemented to derive the phase function (PF) from AC9 and VSF-3 data. b was calculated fitting a Fournier-Forand PF to the normalized VSF data. b was similar to Petzold, but the PF differed in the backwards direction. Some of the sIOPs showed a bimodal distribution, indicating different water types-e.g., coastal vs. open sea. This seems to be partially caused by the distribution of inorganic particles that fall out relatively close to the coast. In order to improve remote sensing retrieval from Baltic Sea data, one should apply different parameterization to these distinct water types, i.e., inner coastal waters that are more influenced by scattering of inorganic particles vs. open sea waters that are optically dominated by CDOM absorption.

Monitoring Coastal Lagoon Water Quality through Remote Sensing: The Mar Menor as a Case Study

“…where the subscripts sw, ph, CDOM, and NAP designate, respectively, seawater (sw), phytoplankton (ph), the combined contribution of colored dissolved organic matter (CDOM), and non-algal particulate (also detrital) matter (NAP); the absorption is not separated owing to the similarities in the spectral shapes of the components [48][49][50][51].…”

“…The slope factor of a CDOM was derived through nonlinear curve fitting between 412 nm and 510 nm (including the reference data set, see below). As such, the slope values presented here are used as a metric to compare the CDOM slope between data sets [51].…”

Synergy of Satellite, In Situ and Modelled Data for Addressing the Scarcity of Water Quality Information for Eutrophication Assessment and Monitoring of Swedish Coastal Waters

“…The bloom is also maintained by high water temperature and stable weather conditions and is easily detected on satellite imagery which allows us to characterize their spatial extent [59,71]. However, the high proportion of cyanobacteria causes increased scatter (due to their internal gas vacuoles) which may affect CHL-a retrieval from satellite [72]. Later in the fall, when biomass declines approaching its annual minimum where conditions are characterized by low temperatures and light availability, limiting primary production.…”

“…Nonetheless, there are certain cold-water phytoplankton groups such as diatoms that manage to survive at low concentrations in winter and thrive during early spring [70]. These seasonal changes in phytoplankton phenology as well as in run-off affect the inherent optical properties in the water, namely the absorption and scattering properties [72].…”

Editorial for the Special Issue “Remote Sensing of Water Quality”

“…Kratzer and Moore [9] offered improvements for the retrieval of chlorophyll, colored-dissolved organic matter (CDOM) and SPM in the Baltic Sea through improved parameterization of the specific inherent optical properties (sIOPs) used in spectral inversion models. Generally, the contribution of CDOM was underrepresented, while chlorophyll and SPM were overrepresented relative to reference datasets (NOMAD/COLORS).…”