Impact of Thermohaline Conditions on Vertical Variability of Optical Properties in the Gulf of Finland (Baltic Sea): Implications for Water Quality Remote Sensing

Vertical variability of inherent optical properties (IOPs) affect the water quality retrievals from remote sensing data. Here, we studied vertical IOPs and simulated apparent (AOPs) in Gulf Finland (Baltic Sea) under three characteristic (non)stratification conditions. In case mixed column, optically significant constituents (OSC) was relatively small. While stratified column surface layer were times higher compared to below thermocline strongly correlated with physical parameters (temperature, salinity). Measurements showed that ratio scattering ( b (440)) absorption a changed (440)/ (440) < 1) i.e., became dominant component attenuation while opposite is true for upper layer. Simulated (from IOPs) spectral irradiance reflectance R λ )) diffuse coefficient K d deeper layers (below thermocline) have significantly smaller magnitude smoother shape. This becomes relevant during upwelling events—a common process coastal Baltic Sea. We quantified effect on using AOPs. The AOPs measurements) decrease signal up 68.8% an increase depth z 90 (λ)) 2.3 4.3 m green part spectrum upwelled mass reaches surface. waters ) PAR region (400–700 nm) by 6.8% (surface 20 depth) observed, chlorophyll- (Chl- total suspended matter (TSM) 31.7 42.1%, respectively. (490)/ (560)≥0.77 indicates also mass. study that, addition biological activity, horizontal transport OSC, temperature changes, alters measured sensor. Knowledge about relation can help parametrisation algorithms retrieving estimates regions.