Scientists from Marine Hydrophysical Institute of RAS have performed the first study of the new HawkEye satellite in dust aerosol conditions over the Black Sea. The results of the work, published in the prestigious scientific journal Atmosphere, will help to significantly improve the accuracy of satellite measurements of sea surface state.
HawkEye satellite, launched in 2018, is designed to monitor the color of the ocean and has the highest spatial resolution among similar instruments. It is especially valuable for studying coastal zones and inland seas, such as the Black Sea. However, its measurements can be distorted due to the presence of dust aerosol in the atmosphere, which is often carried over the Black Sea from the Sahara Desert and the Middle East.
A team of researchers from Marine Hydrophysical Institute of RAS carried out a comprehensive analysis of HawkEye satellite data for 2021-2022. Scientists compared satellite measurements with ground-based data obtained at AERONET stations, as well as with information from other satellites.
"Three employees of Marine Optics and Biophysics Department, Marine Hydrophysical Institute of RAS took part in the work. Each of us had our own tasks: analysis of HawkEye satellite data array, modeling of air flow transport data and analysis of in-situ data, as well as mathematical processing of these data. The dates of dust transport over the Black Sea were determined using visual analysis of satellite images, trajectory analysis with inverse kinematics HYSPLIT, CALIPSO aerosol stratification, and typification maps, as well as the SILAM global forecasting model. During a comparative analysis of in-situ and satellite measurements of reflection coefficient via remote sensing, we discovered an error in the atmospheric correction of HawkEye measurements both for a clear atmosphere and in the presence of absorbing aerosol," says the author of the article, junior research associate at Marine Optics and Biophysics Department of FSBSI FRC MHI Daria Kalinskaya.
The researchers performed a detailed comparison of satellite and ground-based measurements of sea surface brightness and atmospheric optical properties such as aerosol optical depth (AOD) and the Angstrom parameter (the exponent in the formula for the dependence of aerosol optical depth on wavelength).
Scientists have found that HawkEye systematically underestimates the values of the sea surface brightness coefficient in the presence of dust aerosol.
"Our study has shown that the measurement error of HawkEye is associated with an incorrect estimation of the atmosphere optical properties, in particular, the Angstrom parameter," explains Daria Kalinskaya. "In this work, it was calculated that for the Black Sea region this parameter is approximately twice as high as that specified in the standard model for processing satellite data."
The authors found that dependence of atmospheric correction error on the wavelength has the form of a power function with an index from –3 to –9. Moreover, the error is especially large in the short-wave part of the spectrum (412-443 nm).
Based on the obtained results, the scientists proposed a method for correcting the HawkEye data processing algorithm taking into account regional features of the atmosphere over the Black Sea. This approach can also be applied to other water areas of the World Ocean where sufficiently detailed ground measurements of the atmosphere optical characteristics take place.
"To improve the quality of HawkEye satellite products, regional recalculation of the model fixed values of the main optical characteristics is required. We hope that our work will open the way to a significant increase in the accuracy of satellite measurements of the sea surface state not only for the Black Sea, but also for other regions affected by dust aerosol," emphasizes Daria Kalinskaya.
The study was carried out within the framework of the state assignment of Marine Hydrophysical Institute of RAS on theme FNNN-2024-0012 "Analysis, diagnostics, and operational forecast of state of hydrophysical and hydrochemical fields of sea waters based on mathematical modeling using data from remote and contact measurement methods" ("Operational Oceanology").