ASSESSMENT OF THE CURRENT ECOLOGICAL STATE OF THE FASTIV RESERVOIR USING GROUND AND SATELLITE DATA

The article presents the results of researches on assessing the ecological state of the Fastiv Reservoir using ground and satellite data according to the developed scientific approach, which provides for the following sequence for a water body with a large area: conducting field observations, involving satellite information, and creating a resulting map of the current ecological state based on a certain set of indicators, which is the goal of the research. The relevance of the research is defined by the significant deterioration of the water condition in the reservoir, which was caused by an increase in air temperature, uneven distribution of precipitation throughout the year, a decrease in the reservoir filling to 92.7% of the design level, intensive increase in water use and discharge of domestic wastewater. In the conducted studies, it was advisable to compensate the lack of spatially concentrated information (from points of field measurements) with spatially distributed information. During field surveys, hydrobiological and physicochemical indicators were determined in 3 sections of the reservoir - points observations, and maps of water depth, temperature, and transparency were created based on the results. Such results of field observations as an increased turbidity and low transparency made it necessary to use satellite data, especially those containing red and infrared ranges, when calculating spectral indices. From the perspective of remote sensing, water bodies have their own spectral characteristics, which depend on the concentration of various substances dissolved and suspended in water - diffuse reflectance. To compensate the lack of information, the Sentinel-2 L2A image was used, which is the closest with no cloud cover to the date of field observations, and spectral indices were calculated in the open software product Land Viewer: NDVI, GCI, NDWI. Only the NDWI map was useful, providing an insight about the transparency within the entire reservoir. The obtained comprehensive information made it possible to create a resulting map of the current ecological state of the Fastiv Reservoir based on the ground and satellite data.