Pressure and temperature determination using oxygen bands measured by the MAESTRO instrument on SciSat-1

The MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) space instrument was successfully launched on Canada's SciSat-1 satellite in August 2003 as part of the Atmospheric Chemistry Experiment (ACE) payload. MAESTRO is a UV-Visible-NIR dual grating spectrometer taking solar occultation and nadir backscatter spectra of the atmosphere to investigate the dynamical and chemical processes affecting stratospheric ozone distribution. On-orbit solar occultation measurements of temperature and pressure vertical profiles are desirable for accurate retrievals of aerosols and trace gas species from the instrument, as well as for incorporation into dynamical models of the atmosphere. Molecular oxygen is vertically well-mixed in the atmosphere and radiatively active in three strong absorption bands in the visible (γ band) and near-infrared (A and B bands), and can be used for temperature and pressure retrievals from orbit. While the O₂ A-band is the strongest feature in this spectral region and traditionally better studied than the other bands, the MAESTRO instrument is also exploiting the B and γ bands, which are much weaker but have less saturation problems than the A-band at lower tangent heights. This paper will discuss the challenges of correctly computing the profile from these measurements using our current understanding of the band structure and the radiative transfer. Specific examples will be shown demonstrating the need for precise models of both the instrument and the atmosphere in order for this effort to succeed. Results from field-deployments of MAESTRO prototype instruments on high altitude balloons will also be discussed since comparisons can be made with independent measurements of temperature and pressure profiles from the same campaigns.