Effects of different conditions on particle dynamics and properties in West-Estonian coastal areas

Satellite sensors are used to monitor water on a large scale. One of the key vari-ables defining the water-leaving signal is suspended particulate matter (SPM) and thus it is important to understand its properties to improve remote sensing algorithms. However, only a few studies investigating the variability of SPM properties (concentration, nature and size) un-der different seasonal, weather and geographical conditions have been carried out in the Baltic Sea. We focused on relatively shallow areas (maximum depth of 10 m) where there is strong sediment transport by rivers and resuspension of the particles by wave action and advection by currents. Eleven field campaigns were conducted using a set of instruments measuring inher-ent optical properties, auxiliary data, and, in Parnu Bay, also particle size distributions. The results showed that the SPM concentrations, particulate absorption, mass-specific particulate scattering, and backscattering varied temporally and spatially from 5.5-19.6 g m-3, 0-5.62 m-1, 0.08-1.45 m 2 g-1, and 0.0009-0.25 m 2 g-1, respectively. The spectral backscattering ra-tio, which in general is considered to be constant in bio-optical remote sensing algorithms, was actually wavelength-dependent and varied between 0.005 and 0.09 depending on the origin of the particles (organic or mineral matter), particle size distribution, weather conditions, and location. In situ particle size measurements in coastal waters of Parnu Bay also showed that resuspended fine clay particles agglomerated into flocs of > 30 mu m in the brackish waters of the Baltic Sea having random shapes and different sizes.(c) 2022 Institute of Oceanology of the Polish Academy of Sciences. Production and host-ing by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).