The performance of various standard algorithms for the retrieval of suspended particulate matter (SPM) from Sentinel-2 MSI and Landsat-8 OLI satellite data obtained in 2019 and 2021 is discussed. The study was conducted for the estuaries of 2 mountainous rivers originating in the Caucasus Mountains: the Sulak River flowing to the Caspian Sea and the Mzymta River flowing to the Black Sea. The rivers differ in the degree of flow control and the composition of terrigenous suspended matter carried to the sea. The main objective of the study was to compare SPM retrieval results of the C2RCC (Case 2 Regional Coast Color) processor and the ACOLITE (Atmospheric Correction for OLI ‘lite’) algorithms Nechad 2009, Nechad 2015 and Dogliotti. The satellite data were verified against in situ measurements of turbidity and SPM performed synchronously with the satellite survey. Field measurements from a small boat were performed in April and May 2019, 2021 in the northeast Black Sea, in the mouth area of the Mzymta, and in May 2021 in the Sulak mouth area. The measuring instruments and methods included a turbidity sensor mounted on a CTD (conductivity / temperature / depth) probe, a portable turbidimeter, and water sampling for further laboratory analysis. It was established that for low SPM, 20-30 g/m3, performances of C2RCC and Nechad 2015 practically coincided and correlated well with the in situ data. For large SPM, over 300 g/m3, the best performance was demonstrated by Dogliotti, an algorithm designed especially for extreme SPM values.
We present results of observations of vortex structures in the Caspian Sea based on satellite images of the visible range obtained by Sentinel-2 (MSI), Landsat-5 (ТМ), Landsat-7 (ETM+) and Landsat – 8 (OLI). The initial goal of this work was to identify vortex structures and their main localization areas in the Caspian Sea. In this paper we used Ocean Color Data for two periods: 1999-2006 and 2007-2013, plus 2 recent years (2019 and 2020). Results of these periods were comparing between each other. About 50% of the scenes from the obtained data are covered by clouds due to difficult weather conditions over the Caspian Sea - a frequent changes of air masses in all seasons of the year. Among cloudless scenes, on average, vortex structures occur on 20-30% of scenes. According to the results of the analysis of the data obtained, a predominance of submesoscale cyclones and anticyclones is noted. It was noted that vortex structures were mainly found in the shelf zone of the Caspian Sea. More intense vortex formation is observed in the South Caspian. The main reasons for their formation: the flow of river runoff, complex bottom and coastal topography, the vorticity of the wind field, shear instability at the periphery of the main circulation elements. The mapping of the main circulation elements in Caspian Sea was carried out. For each part of the Caspian Sea, the six main areas of vortex formation were identified.
Waters from a closed Vistula lagoon actively influences the southeastern part of the Baltic Sea (offshore Kaliningrad region). When entering the Baltic Sea lagoon waters become a perfect tracer to track different hydrodynamic and biological processes with the help of Ocean Color Data. The research is primarily based on remote sensing data being a first step to determine properties and propagation boundaries of the outflow into the open Baltic Sea. During research we could analysis different types of remote sensing data including color composite images from MODIS Terra/Aqua, OLI/TIRS Landsat 8; MSI Sentinel 2; OLCI Sentinel 3. The oceanographic experiments include CTD transects and determination of turbidity and CHL-a concentration in outflow waters to describe water properties of the outflow and provide verification of satellite data. Results of a combined experiment for determination of the Vistula Lagoon outflow distinctive features with the use of satellite images from optical sensors and oceanographic in-situ data are shown.
River flow is the main source of dissolved and suspended substances entering to the sea, including products of anthropogenic pollution. Coming from the river to the sea, the continental waters form submesoscale structures adjacent to the estuary, distinguished by low salinity and temperature different from the surrounding, and also, increased turbidity, high content of suspended matter and dissolved organics. Such structures are called "Plumes". Traditionally, we can divided two research methods - contact (in-situ/ship measurements) and non-contact (remote sensing data). But, basically the joint use of in-situ measurements and remote sensing data in existing scientific works - is nominally, each source of information is used separately, and more often direct (in-situ) measurements are preferred, and remote sensing data is used as an auxiliary method for qualitative descriptive works. And there is still no reliable information on the extent to which quantitative estimates can be trusted, obtained from remote sensing data, especially in such difficult estuary areas. In this paper, we present the results of verification satellite data in the optical range with the aim of comparing quantitative data in the river-mouth area obtained by contact (field measurements near river mouth in northeastern part of Black sea) and contactless methods.
Vortex structures of different types are common in the Southeastern Baltic Sea. Intensive western winds, a complex coastline and an absence of steady currents make this region very appealing for studying the nature of vortex processes. These processes are clearly identified from Space. We present results of a multi-year satellite monitoring of mesoscale and submesoscale vortex structures in the Southeastern part of the Baltic Sea and of supporting field studies. An important part of our work was accumulation of remote sensing data as the first step in evaluation of circulation patterns and vortex structures presented on the sea surface. An analyzed remote sensing data include color composite images from MSI Sentinel-2, OLI Landsat-8 and ETM+ Landsat-7 as well as radar images from Sentinel-1 and Radardsat-2 that also provide a powerful tool for an identification of circulation processes on the sea surface. Continuous monitoring of the Southeastern Baltic Sea with an analysis of satellite visual and radar images show that the Gulf of Gdańsk is the most frequent area with mesoscale and submesoscale eddies. They appear in this area mostly in summer and mainly under the atmospheric influence. Some eddies remain stable for at least of 8 days and could be easily tracked on color composite images. The other area of the vortex structure was determined to the north of the Cape Taran. In summer months from 2014 to 2018, we performed oceanographic concurrent experiments in the southeastern part of the Baltic Sea. Field studies of spatial and temporal characteristics of vortex structures proved results found by an analysis of satellite images.
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