Satellite remote sensing techniques for detection of riverine and other sources flows in the coastal part of the Black Sea

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.