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.
The SWIFT instrument is an imaging, field-widened Michelson interferometer designed to measure stratospheric winds passively from orbit by detecting the Doppler shift of naturally occurring O3 thermal emission. It has been selected for flight on NASDA's
GCOM-A1 satellite, scheduled for launch in 2007. It is similar in principle to the Wind Imaging Interferometer (WINDII) on UARS but whereas WINDII operates in the visible with a CCD detector, SWIFT will operate at a wavelength of 8.823μm and use a HgCdTe array detector. This spectral region is very crowded with emission lines
and a substantial effort was needed to select appropriate candidate lines. Designing filters for this instrument has also proved to be challenging because of the narrow bandwidth required to isolate the emission line, combined with the need to fill the field of view and minimize the effects of thermal drifts. SWIFT will carry blackbody
sources for responsivity calibrations and three NH<sub>3</sub> cells that provide a narrow emission line to be used as a secondary phase standard. This paper discusses the design of the filters for SWIFT and associated calibration issues.
The Stratospheric Wind Interferometer For Transport studies (SWIFT) is a passive sensor designed to measure winds in the stratosphere from a satellite. It is a field-widened Michelson interferometer very similar to the WINDII instrument on UARS but operates in the mid-IR, where it detects the Doppler shifts of atmospheric thermal emission lines of ozone. SWIFT uses a HgCdTe array detector to view the emission at the Earth's limb. Measurements are subsequently inverted by computer to obtain true vertical profiles of the stratospheric wind in the altitude range 20 to 40 km. Two orthogonal fields of view allow wind vectors to be obtained by combining the components observed from different directions a few minutes apart. Prototype Ge wafer etalon filters and a field-widened Michelson interferometer for the Mid-IR have been built and tested, with good results. Modeling studies indicate that a measurement precision of 5 m/s can be obtained throughout the altitude range of interest. In addition to the winds, SWIFT will measure ozone densities in the stratosphere. SWIFT has been selected for flight on NASDA's GCOM-A1 satellite and a Phase A study is being supported by ESA and the Canadian Space Agency.
SWIFT is a small (< 85 kg, approximately 0.5 m<SUP>3</SUP>, < 100 W) satellite instrument which is designed to accurately measure global horizontal winds and ozone concentrations in the stratosphere. SWIFT is similar to the highly successful WINDII instrument currently operating on the UARS satellite. Both use a field-widened Michelson interferometer set at high path difference to image the Doppler shift of atmospheric emission. The data set provided by SWIFT will provide essential input to the next generation of Numerical Weather Prediction (NWP) models which are currently being developed by meteorological organizations worldwide. SWIFT is currently a leading candidate to fill the foreign instrument opening for the NASDA GCOM-A1 mission, providing highly complimentary data to the ODUS and SOFIS instruments. SWIFT allows direct measurement of stratospheric dynamics and high vertical resolution ozone profiling to maximize the scientific return for this mission.
The Stratospheric Wind Interferometer for Transport Studies (SWIFT) is a satellite-born limb-viewing instrument which will be capable of globally measuring horizontal winds at altitudes of between 20 and 40 km with a precision of < 5 m/s, a vertical resolution of 2 km and a horizontal resolution on the order of a hundred km. SWIFT will map stratospheric dynamics. The data from the instrument will be important input for models which seek to predict the global distribution of stratospheric ozone. In addition, the SWIFT data will provide observational input to tropospheric weather models, which are currently being extended to the stratosphere. With global stratospheric wind data, these enhanced models have the potential to significantly improve weather forecasting in the troposphere. The instrument will observe a thermal emission line of an abundant atmospheric constituent near 8 micrometers using a field widened Michelson interferometer. A doppler shift of the emission line is detected as a phase shift at the output of the interferometer. A 2D array detector monitors the phase both perpendicular to and along the limb, thus mapping the velocity field. The fundamental feasibility of the instrument will be shown. The basic instrument requirements are described and the instrument parameters are derived from them. The instrument will utilize radiatively cooled optics and Stirling cycle coolers for the detector and filters. This instrument will be suitable for inclusion on a medium to large satellite with multiple instruments. The lack of cryogens is consistent with its intended use on the operational weather satellites of the future.
The wind imaging interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) is a CCD imager which views a selection of airglow emissions at the limb through a field-widened Michelson interferometer. Winds are calculated from the Doppler shifts of the spectral lines, detected as changes in the phase of the fringes. WINDII has been operating in space for almost three years and its performance has been monitored over that time. It continues to function well, though subtle changes have been seen. This paper is a discussion of the endurance of the instrument and of the changes that have occurred during the mission.
WINDII is an imaging, field widened Michelson interferometer built by Canada and France for flight on NASA's Upper Atmosphere Research Satellite, which was launched September 12, 1991. Its primary purpose is to measure winds in the 80-300 km region of the atmosphere by measuring the Doppler shift of the airglow emissions. This paper discusses the design, testing and performance of the baffle system used for daytime observations.