Pressure/temperature and volume mixing ratio retrievals for the Atmospheric Chemistry Experiment (ACE)

Scisat-1, otherwise known as the Atmospheric Chemistry Experiment, is a satellite mission designed for remote sensing of the Earth's atmosphere using occultation spectroscopy. The primary goal of the mission is to investigate the chemical and dynamical processes that govern. ozone distribution in the stratosphere and upper troposphere. It has been developed under the auspices of the Canadian Space Agency and is scheduled for launch in December of 2002. The primary instrument on board Scisat-1 is a high resolution Fourier transform spectrometer (FTS) operating in the infrared. Pressure and temperature as a function of altitude will be determined from the FTS measurements through analysis of carbon dioxide absorption. Volume mixing ratio (vmr) profiles will be retrieved for more than thirty molecules of atmospheric interest. Both the pressure/temperature and vmr retrievals use non-linear least squares Global Fit type approaches. For the pressure/temperature analysis, several variations are being developed; the choice of which version to implement depends on the quality of the pointing information obtained from the satellite. In the case of poor pointing knowledge, tangent height separations between measurements will be determined directly from the FTS data (simultaneously with the pressure and temperature determination) through the imposition of hydrostatic equilibrium.