Retrieval of Atomic Oxygen and Temperature in the Thermosphere, 1. Feasibility of an Experiment Based on the Spectrally Resolved 147 Micrometer Limb Emission.

摘要

The importance of atomic oxygen and translational temperature in mesospheric/thermospheric processes is the motivation to study the feasibility of recovering vertical profiles of the temperature and O-atom density from limb scan data obtained near 147 micrometer and/or 63 micrometer wavelength, corresponding to the oxygen atom ground electronic state (OI) transitions. The limb radiance data must be spectrally resolved to recover both temperature and atomic oxygen density if only one of the OI lines is used, which is the approach investigated in this report. We show how the two vertical profiles can be recovered by applying an onion-peeling method to synthetic data. The temperature and O-atom density in each peeled layer are obtained simultaneously by nonlinear least-squares spectrum fitting. Spectral data in the 147 micrometeer line was found to yield reasonable accurate and stable profiles from 300 km down to an altitude between 130 and 90 km, ...depending on the noise level and spectral resolution, and gave better results than the stronger 63 micrometer data below 140 km. We estimate that the S/N and spectral resolution required for successful retrievals could be provided by a confocal Fabry-Perot system operating near 147 micrometers although retrievals down to 90 km from data obtained at orbital altitude would require cooled foreoptics roughly a meter in diameter. (AW)