Halogen Occultation Experiment (HALOE) altitude registration of atmospheric profile measurements: lessons learned and improvements made during the data validation phase

摘要

Abstract: Measurements by the Halogen Occultation Experiment (HALOE), on board the Upper Atmosphere Research Satellite (UARS) are producing high quality atmospheric profiles of trace gases involved in ozone chemistry. Using eight IR channels to sense the atmospheric absorption of sunlight, HALOE is providing scientists with high quality global fields of HCl, HF, O$-3$/, CH$-4$/, NO, NO$-2$/, H$-2$/O, aerosol extinctions and temperature, shedding new light on the dynamics and chemistry of the atmosphere. Critical to the retrieval of atmospheric constituent profiles from space-borne spectroscopic sensors is the ability to determine the true path through the atmosphere of measured radiation. Since becoming operational in October 1991 new effort has been put into validating and refining the techniques required to estimate the tangent point altitude associated with each signal sample. This is accomplished by measuring transmission of sunlight in the CO$-2$/ 2.8 micron region, and registering the CO$-2$/ transmission profile with a modeled transmission profile based on temperature and pressure data from NMC or UKMO and an assumed CO$-2$/ mixing ratio. In this paper we report on lessons learned during the data validation phase, and improvements made to the altitude registration process. The parameters and processes involved include CO$- 2$/ limb radiance inversion, signal processing, zenith angle estimation, refraction calculations, registration regions and aerosol effects. We also present the results of sensitivity and error analyses which reveal the accuracy required for each estimated parameter in order to register within the specified error budget. !3