An evaluation of Odin/OSIRIS limb pointing and stratospheric ozone through comparisons with ozonesondes

Abstract

Five-plus years of Odin/OSIRIS (Optical Spectrograph and Infrared Imager System) ozone profiles (version 3.0 and SaskMART) have been compared with coincident ozonesonde profiles from the tropopause to the middle stratosphere (~10–35 km). The OSIRIS(v3.0)-sonde comparisons, together with the “knee” technique, suggest that OSIRIS pointing is stable with an accuracy (systematic uncertainty) of 100~m and a precision (random uncertainty) of 400 m. Comparison of coincident profiles revealed excellent overall agreement with differences generally not exceeding 10% between 10 and 35 km. During periods of satellite eclipse larger differences above 25 km were found and concluded to be the result of flexing of the spacecraft frame brought about by cooling. Uncertainties derived from the intercomparison suggest an OSIRIS precision of 25–30% at 10 km, reaching a minimum of about 4–6% in the middle-stratosphere (23–28 km), and 6–8% at 35 km. Ozonesonde uncertainties were also derived and found to be slightly larger in the tropics than mid-latitudes, possibly due to a lack of column normalization at some of the tropical stations. OSIRIS SaskMART ozone, an alternative ozone data product, was found to be very comparable with the v3.0 ozone, with slightly smaller biases relative to the ozonesondes. OSIRIS is concluded to be a robust and accurate source of stratospheric ozone profiles. PACS Nos.: 82.33.Tb, 95.75.Qr, 42.68.–w