VALIDATION OF MEASUREMENTS OF CARBON-MONOXIDE FROM THE IMPROVED STRATOSPHERIC AND MESOSPHERIC SOUNDER

Carbon monoxide abundances in the middle atmosphere are retrieved from infrared measurements of the emission of this molecule at 4.6 mu m ta ken by tire improved stratospheric and mesospheric sounder (ISAMS) on board the Upper Atmosphere Research Satellite. In addition to a limite d signal-to-noise ratio, the measured radiances include significant co ntamination by other compounds in the stratosphere and show clear non- local thermodynamic equilibrium effects in the mesosphere which also a ffect the stratospheric limb views. The application of the ISAMS retri eval method to these measurements and the particularly method followed to deal with these difficulties are described. The actions carried ou t to understand and validate the obtained CO abundances are detailed. They include analysis of the radiances, sensitivity studies of the pro duct to retrieval parameters, evaluation of the main sources of system atic and random errors, and comparisons with theoretical model predict ions and with the few correlative measurements available. The gross fe atures observed in the CO distribution present good agreement with dyn amical-chemical models of the middle atmosphere. The aspects of the re trieval that need further improvement are identified, and the global q uality of the database and the expectations for its scientific use are discussed.