The PCW (Polar Communications and Weather) mission is a dual satellite mission with each satellite in a highly eccentric orbit with apogee ~42,000 km and a period (to be decided) in the 12–24 hour range to deliver continuous communications and meteorological data over the Arctic and environs. Such as satellite duo can give 24×7 coverage over the Arctic. The operational meteorological instrument is a 21-channel spectral imager similar to the Advanced Baseline Imager (ABI). The PHEOS-WCA (weather, climate and air quality) mission is intended as an atmospheric science complement to the operational PCW mission. The target PHEOS-WCA instrument package considered optimal to meet the full suite of science team objectives consists of FTS and UVS imaging sounders with viewing range of ~4.5° or a Field of Regard (FoR) ~ 3400×3400 km<sup>2</sup> from near apogee. The goal for the spatial resolution at apogee of each imaging sounder is 10×10 km<sup>2</sup> or better and the goal for the image repeat time is targeted at ~2 hours or better. The FTS has 4 bands that span the MIR and NIR with a spectral resolution of 0.25 cm<sup>−1</sup>. They should provide vertical tropospheric profiles of temperature and water vapour in addition to partial columns of many other gases of interest for air quality. The two NIR bands target columns of CO<sub>2</sub>, CH<sub>4</sub> and aerosol optical depth (OD). The UVS is an imaging spectrometer that covers the spectral range of 280–650 nm with 0.9 nm resolution and targets the tropospheric column densities of O<sub>3</sub> and NO<sub>2</sub> and several other Air Quality (AQ) gases as well the Aerosol Index (AI).
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<sup>-1</sup>. 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<sup>-1</sup> with a full-width at half-maximum of ~0.1 cm<sup>-1</sup> 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<sup>-1</sup> are obtained.