Purpose. The purpose of the study is to obtain quantitative estimates of regional coefficients for calculating the values of suspended matter concentrations in the surface layer of the northern and northeastern parts of the Black Sea based on a Quasi-Analytical Algorithm (QAA version 6) and daily multi-sensor data (SeaWiFS, MODIS, MERIS, VIIRS and OLCI) with spatial resolutions of 1 and 4 km.

Methods and Results. The paper presents in situ data on the values of mass concentration of suspended matter ≥ 0.2 μm in the surface layer of the northern and northeastern parts of the Black Sea obtained during the 138th cruise of the R/V Professor Vodyanitsky (November 14 – December 9, 2025). A total of 56 seawater samples were collected and processed at 56 stations. The volume of each sample pumped through a filter varied from 1.24 to 8.17 L and depended on the suspended matter content of the seawater. The backscattering coefficient values at 560 nm were calculated using multi-sensor (SeaWiFS, MODIS, MERIS, VIIRS and OLCI) data on the spectral radiance of the sea at spatial resolutions of 1 and 4 km and the Quasi-Analytical Algorithm (QAA version 6). The relationship between the above-mentioned coefficient and the suspended matter concentration was investigated. The study results made it possible to determine the values of regional coefficients in the linear regression equation that relates the backscattering coefficient to the suspended matter concentration.

Conclusions. In the area under study, the suspended matter concentration varied widely, from 0.17 to 1.48 mg/L. Higher values were observed near the Kerch Strait (1.2–1.48 mg/L) and Feodosia Gulf (0.9–1.2 mg/L). Lower values (0.17–0.55 mg/L) were characteristic of the deep part of the sea. The linear regression parameters relating the backscattering coefficient to the suspended matter concentration for the data with a 4-km resolution were 89.2±6.3 slope and 0.24±0.03 intercept), and those for the data with a 1-km resolution were 102.6±7.3 and 0.21±0.03 respectively. A comparison of the calculated suspended matter concentration values with the measured ones indicated a high accuracy of the obtained estimates: the median absolute percentage deviation was 20% (4 km) and 19% (1 km), the median absolute difference was 0.09 mg/L (at both resolutions), the systematic error was −0.2% (4 km) and −0.1% (1 km), and the coefficient of determination was 0.82 (at both resolutions).