Data retrieval and error analysis study on the measurement of stratospheric winds with a Michelson interferometer

Abstract

The Stratospheric Wind Interferometer for Transport studies (SWIFT) instrument is designed to measure stratospheric winds in the altitude region of 20-45 km with a target accuracy of 3-5 m s^-1. It is one of two scientific instruments on the Greenhouse Gases Observations Satellite (GOSAT) proposed for launch in 2008. The winds are to be determined by measuring the Doppler shift of thermal emission lines in a narrow spectral range using a limb viewing field widened Michelson interferometer. The instrument spectral range for this study is centered about a reference ozone line at 1133.4335 cm^-1 with a full-width at half-maximum of ~0.1 cm^-1 for the instrument transmittance function. Measurement simulation and data retrieval are applied in the present investigation to evaluate and elaborate on measurement and processing conditions required to satisfy the desired wind accuracy. The related principles, processes, and tools are summarized. Radiative transfer and instrumental measurement simulations are conducted to produce raw image measurements. These raw images are processed up to and including inversions performed using the maximum a posteriori solution equation with differential regularization. In addition to retrieving the Doppler wind and ozone number density profiles, allowance is made to investigate the additional recovery of parameters such a pressure scaling factor and profiles of temperature and nitrous oxide. Retrieval characterization and an error analysis have been undertaken. Introductory results are presented. Retrieval Doppler wind noise levels of under 3 m s^-1 are obtained.