The Global Ozone Monitoring by Occultation of Stars(GOMOS) instrument uses stellar occultation technique for monitoringozone, other trace gases and aerosols in the stratosphere and mesosphere. Theself-calibrating measurement principle of GOMOS together witha relatively simple data retrieval where only minimal use of a prioridata is required provides excellent possibilities for long-termmonitoring of atmospheric composition.GOMOS uses about 180 of the brightest stars as its lightsource. Depending on the individual spectral characteristics of thestars, the signal-to-noise ratio of GOMOS varies from star to star,resulting also in varying accuracy of retrieved profiles. We presenthere an overview of the GOMOS data characterisation and errorestimation, including modeling errors, for O3, NO2,NO3, and aerosol profiles. The retrieval error (precision) ofnight-time measurements in the stratosphere is typically 0.5–4% forozone, about 10–20% for NO2, 20–40% for NO3 and 2–50%for aerosols. Mesospheric O3, up to 100 km, can be measured with2–10% precision. The main sources of the modeling error areincompletely corrected scintillation, inaccurate aerosol modeling,uncertainties in cross sections of trace gases and in atmospherictemperature. The sampling resolution of GOMOS varies depending on themeasurement geometry. In the data inversion a Tikhonov-typeregularization with pre-defined target resolution requirement isapplied leading to 2–3 km vertical resolution for ozone and 4 km resolutionfor other trace gases and aerosols.
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