Feasibility of Satellite Radar Observation of River and Lagoon Plumes in the Southeastern Baltic Sea

The article considers the features of manifestation of coastal plumes formed by the Vistula outflow and the outflow of waters from the Vistula and Curonian Lagoons in the coastal zone of the southeastern Baltic Sea in satellite radar images of the sea surface. The experimental basis for the study was satellite data obtained for the three areas of interest from May 1, 2022, to April 30, 2024, using C-SAR synthetic aperture radars of the Sentinel-1A and -1B satellites. The study also involved the data from multispectral sensors in the visible range—MSI (Multispectral Instrument) of the Sentinel-2A and -2B satellites and the scanning radiometer OLI (Operational Land Image) of the Landsat-8 and -9 satellites accumulated over the same period. We analyzed coastal plumes’ SAR signatures distinguished by various morphological forms. Summarizing the results of the analysis, we identified and described four primary mechanisms of plume visualization in radar images of the Baltic Sea surface: plumes with a pronounced boundary visible as a line of sharp increase of the backscattered signal; plumes with a boundary outlined by slicks; areas of amplification/weakening of the radar signal in a plume without formation of a pronounced front; and plume manifestation due to tracers, such as ice/accumulation of biogenic films. In the paper, we provide estimates of relative contribution of these mechanisms to the formation of radar signatures of plumes in each of the three test areas. We also discuss plume area determination accuracy based on various satellite data. The paper emphasizes the importance of using satellite SAR data to obtain detailed information on the spatial variability of river and lagoon water distribution in the test areas.