M-124 filter ozonometers are used for total ozone measuring in Ukraine since 1970s. Recently the need to calibrate several M-124 instruments of the Ukrainian filter ozonometer network is raised to continue ozone observations. The calibration became possible owing to the accurate ozone measurements by Dobson spectrophotometer started in 2010 at the Kyiv-Goloseyev WMO station located at the Main Astronomical Observatory of National Academy of Sciences of Ukraine. For calibration purposes the simultaneousM-124 and Dobson Direct Sun measurements were carried out during the 2013-2016 period by researchers from Taras Shevchenko National University of Kyiv and Main Astronomical Observatory. The M-124 instrument has two spectral channels: first is 305 nm andsecond is 325 nm. Outgoing signal from M-124 is determined by transparency of the terrestrial atmosphere and filter characteristics. Theoretical description of the solar radiation propagation through the atmosphere is determined by the Bouguer-Lambert-Beer law taking into account ozone absorption, Rayleigh and aerosol scattering. Parameters of the aerosol scattering have been determined from observations with the CIMEL sunphotometer of Aerosol Robotic Network which is also located at the Kyiv-Goloseye&v station. The ozonometers optical characteristics were studied after M-124 refurbishment and modernization at the Central Geophysical Observatory of Ukraine that includes a significant part of the whole calibration work. Knowing the spectral depende&nce of each filter is necessary to calculate signal ratios in two channels. This information allowed solving the inverse problem of determining total ozone content in the terrestrial atmosphere. Comparison of these results with Dobson spectrophotomet&er data shows their good quality even without an additional correction. These results open a possibility to calibrate M-124 filter ozonometers for future ozone measurements at the observation sites of the Ukraine ozonometer network.
