ALGORITHMS AND SENSITIVITY ANALYSES FOR STRATOSPHERIC AEROSOL AND GAS EXPERIMENT-II WATER-VAPOR RETRIEVAL

This paper provides a detailed description of the current operational inversion algorithm for the retrieval of water vapor vertical profiles from the Stratospheric Aerosol and Gas Experiment II (SAGE II) occultation data at the 0.94-mum wavelength channel. This algorithm is different from the algorithm used for the retrieval of the other species such as aerosol, ozone, and nitrogen dioxide because of the nonlinear relationship between the concentration versus the broad band absorption characteristics of water vapor. Included in the discussion of the retrieval algorithm are problems related to the accuracy of the computational scheme, accuracy of the removal of other interfering species, and the expected uncertainty of the retrieved profile. A comparative analysis on the computational schemes used for the calculation of the water vapor transmission at the 0.94-mum wavelength region is presented. Analyses are also presented on the sensitivity of the retrievals to interferences from the other species which contribute to the total signature as observed at the 0.94-mum wavelength channel on SAGE II instrument. Error analyses of the SAGE II water vapor retrieval will be shown, indicating that good quality water vapor data are being produced by the SAGE II measurements.