The clear and reliable detection of effluent plumes using satellite data is especially challenging. The surface signature of such events is of a small scale; it shows a complex interaction with the local environment and depends greatly on the effluent and marine water constitution. In the context of remote sensing techniques for detecting treated wastewater discharges, we study the surface signature of small river plumes, as they share specific characteristics, such as higher turbidity levels and increased nutrient concentration, and are fresh compared to the salty marine water. The Bulgarian Black Sea zone proves to be a challenging study area, with its optically complex waters and positive freshwater balance. Additionally, the Bulgarian Black Sea coast is a known tourist destination with an increased seasonal load; thus, the problem of the identification of wastewater discharges is a topical issue. In this study, we analyze the absorption components of the Inherent Optical Properties (IOPs) for 84 study points that are located at outfall discharging areas, river estuaries and at different distances from the shoreline, reaching the open sea area at a bottom depth of more than 2000 m. The calculations of IOPs take into account all available Sentinel 2 cloudless acquisitions for three years from 2017 until 2019 and are performed using the Case-2 Regional CoastColour (C2RCC) processor, implemented in the Sentinel Application Platform (SNAP). The predominant absorber for each study area and its temporal variation is determined, deriving the specific characteristics of the different areas and tracking their seasonal and annual course. Optical data from the Galata AERONET-OC site are used for validating the absorption coefficient of phytoplankton pigment. A conclusion regarding the possibility of distinguishing riverine, marine and coastal water is derived. The study provides a sound basis for estimating the advantages and drawbacks of optical satellite data for tracking the extent of effluent and fluvial plumes with unknown concentrations of optically significant seawater constituents.

In this study we investigate the possibility to distinguish between different water types in the Danube delta and the Black Sea coastal zone based on the reflectance spectra. For this we use hyperspectral satellite images from PRISMA (PRecursore IperSpettrale della Missione Applicativa) and multispectral images from Sentinel-2 MSI (MultiSpectral Instrument) in July 2020. The visual inspection of the available acquisitions differentiates between four aquatic types: lagoons; river and stream plumes mixing with marine waters; turbid and optically complex coastal waters; and optically clean waters away from the shore. For each of the four types we determine the characteristic averaged reflectance spectra from PRISMA and Sentinel-2 for the spectral range from 400 nm to 2500 nm. It is found that Sentinel-2 spectra are very similar for the 4 water types, in contrast to the PRISMA spectra which give substantial additional information. Further we analyse the gradual modification of the characteristic hyper- and multispectral spectra from the shoreline to the open sea (∼25 km distance) in 15 locations passing through areas of varying turbidity. We demonstrate that the intensity of surface reflectance from the hyperspectral instrument decreases gradually with distance from shoreline, clearly showing the transition zone between riverine and marine water. The multispectral reflectance spectra for the same study areas did not present such consistent behaviour. The presented results demonstrate the benefits of hyperspectral over multispectral images for turbid aquatic regions in the Black Sea coastal zone. They show that with little requirements regarding pre-processing and computational resources hyperspectral data can contribute greatly to classification of water types, in respect of their turbidity.

This article is dedicated to the earthquakes of February 6th, 2023 in Türkiye and Syria. The epicenters are located in seismically active region where the East Anatolian Fault is placed. Past and present seismicity is reviewed and together with the aftershock activity is shown as simplified map. The tectonic and geological features of the affected area are discussed in brief. Preliminary assessments of the consequences and damages are presented, according to the data we known up to now. In addition, the main shock generated tsunami waves that were registered by the mareograph network. Using SAR satellite data, we made an estimation of the deformations in the Earth’s crust after the earthquakes. The preliminary results show displacements above 2.5 m.

Poorly treated or completely untreated sewage water discharges are common problem which might have major consequences in coastal water regions, smaller water basins and semi-enclosed seas. Although satellite remote sensing has a great potential for coastal water quality monitoring such outfalls are difficult for detection due to the small scale of the events and the complex effects on the physical and biogeochemical parameters. In search for an appropriate technique for detection of  sewage discharges through satellite remote sensing, we examine areas with similar optical water properties, such as small river plumes flowing into the sea. They are expected to be visible in a similar manner as they have high turbidity levels, higher nutrients concentration and are fresh compared to the salty sea water.In the current study we examine small river inflows in the Black Sea as they have optical and radar properties comparable with poorly or completely untreated sewage discharges in the region. Additionally, the Black Sea is an intriguing study area because of the unique ecosystem with challenging optical properties and water characteristics.The temporal and spatial variability of the inherent optical properties and sea surface roughness are studied in the area of river plumes and are compared with open sea values. The impact of atmospheric conditions given by wind speed, wind direction and precipitation on the river plume detectability is observed in the regions of interest. Long time series of images for three years are analysed in order to reveal the seasonal and annual variability of the events. The satellite data is taken from the Sentinel missions and the atmospheric variables are from the ERA5 reanalysis.The outcome of the study gives a solid base for estimation of the potential of satellite remote sensing for monitoring of poorly treated or completely untreated sewage outfalls or other land sources flowing into the sea.