Physical inversion of the full IASI spectra: further validation and inter-comparison of O3 and OCS products

Abstract: Results from the physical, simultaneous, inversion of the full IASI (Infrared Atmospheric Sounder Interferometer) spectra applied to the retrieval of surface temperature and emissivity, temperature, water vapour, ozone and HDO vertical profiles, and gas column abundance of CO2, CO, CH4, SO2, N2O, HNO3, NH3, OCS and CF4 have been updated with respect to the validation of OCS and O3 products. A case study has been set up and analysed, which consists of a two years long record of IASI spectra over sea surface in the Pacific Ocean close to the Mauna Loa (Hawaii) validation station. IASI O3 products have been intercompared with OMI (Ozone Monitoring Instrument) O3 retrievals, which, in contrast to IASI that uses the thermal infrared, are based on observation in the near ultra violet region of the electromagnetic spectrum. IASI OCS retrievals are compared to in situ flask observations. The IASI vs OMI comparison shows an excellent agreement with a correlation of 0.97 and a relative bias of approximately 1 Dobson Unit. For the case of OCS, we have found a good correlation of 0.75 for night time soundings. IASI captures the OCS seasonal cycle, although a relatively large negative bias of approximately -74 pptv is seen, which can be explained with a large spectroscopic error for OCS in the HITRAN 2008 version.