Atmospheric correction of satellite optical data is based on an assessment of the optical characteristics of the atmosphere, such as the aerosol optical thickness of the atmosphere and the spectral slope, the so-called Angstrom parameter. Inaccurate determination of these parameters is one of the causes of error in the retrieval of remote-sensed reflectance spectra. In this work, a large array of field and satellite data measured in Sevastopol and the northeastern part of the Black Sea were used, including ship-based measurements of atmospheric characteristics and sea reflectance, MODIS Aqua/Terra, and VIIRS NOAA/NPP Level 2 remote-sensed reflectance and atmospheric data. In total, three episodes of Saharan dust transfer over the Black Sea region were considered, mainly in the autumn-winter period. The purpose of this study was to show the numerical differences between the atmospheric parameters measured at the surface level and by satellites, and show their relationship with the differences between in situ and satellite remote-sensed reflectance. Based on the information identified, we propose an algorithm for additional correction of satellite level 2 data that uses a two-parametric model of the Black Sea remote-sensed reflectance as a first approximation. Moreover, additional correction significantly reduces the discrepancy between in situ and retrieved remote-sensed reflectance, especially in short-wave spectral bands.

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Purpose. The Black Sea region where the forest fires were recorded by the FIRMS system, as well as the atmosphere above it, namely the fire-induced variation of the atmospheric aerosol basic optical characteristics, were the main objects of the investigation. The study is aimed at examining the fires in the Black Sea region in 2018–2019 for assessing correlation between these events and variability of the basic optical characteristics over the Black Sea. Methods and Results. Based on the FIRMS system data, variations of intensity of the fire-induced radiation were studied. The results of statistical processing of the MODIS and VIIRS satellite data on the fires in 2018–2019 were represented. For the dates when the fire numbers were the highest in the Black Sea region, the basic optical and microphysical characteristics of the atmospheric aerosol were analyzed due to the SPM and AERONET data. The dates when the fire intensity was particularly high (based on the MODIS and VIIRS data) were analyzed and compared with the dates when the anomalous values of the atmospheric aerosol optical characteristics were recorded over the region under study. Conclusions. For the fire events in the Black Sea region revealed due to the MODIS and VIIRS data, complex analysis of the air mass transfer was performed by the model HYSPLIT, and the aerosol was typed by the CALIPSO algorithm. On June 22, 2019 the most intense fires were recorded. According to the aerosol typing by the CALIPSO algorithm, on this day the predominant aerosol types were the contaminated dust and smoke. Using the MODIS and VIIRS data, investigation of possible source of the aerosol transfer on this date showed that the area of intense inflammationn and smoke was located to the northeast from the Black Sea region. Since the satellite-derived data on this day showed no dust transfer either from the Sahara or the Syria deserts, it is possible to conclude that increase of the values of aerosol optical depth АОD (500) was conditioned by transfer of the aerosol resulted from biomass burning from the north to the Black Sea region.

The article considers the period of influence of the tropical storm Ophelia on the optical characteristics obtained for the Black Sea region. Over the Black Sea on 18.10.2017-19.10.2017 the transfer of air flows from the northwest was recorded, which contained particles like dust aerosol from the Sahara desert, and smoke particles from fires from the Iberian Peninsula. Analysis of the dust-smoke combined type aerosol influence on the results of satellite spectral brightness coefficient over the Black Sea water area according to MODIS and VIIRS measurements showed an underestimation of the values of Rrs(λ) in the short-wave region compared to in situ data obtained at the western Black Sea stations of the AERONET network.