Yves Joseph Rochon

Atmospheric Chemistry Experiment (ACE): Mission overview

SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earths atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm-1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750-4400 cm-1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285-1030 nm and spectral resolution of 1-2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10-100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results. Copyright 2005 by the American Geophysical Union.

Retrievals for the atmospheric chemistry experiment Fourier-transform spectrometer

SCISAT-1, also known as the Atmospheric Chemistry Experiment, is a satellite mission for remote sensing of the Earths atmosphere, launched on 12 August 2003. The primary instrument on the satellite is a 0.02 cm(-1) resolution Fourier-transform spectrometer operating in the mid-IR (750-4400 cm(-1)). We describe the approach developed for the retrieval of atmospheric temperature and pressure from the troposphere to the lower thermosphere as well as the strategy for the retrievals of volume-mixing ratio profiles of atmospheric species.

Data assimilation with the Canadian Middle Atmosphere Model

Abstract A data assimilation scheme has been coupled to the Canadian Middle Atmosphere Model, providing, for the first time, the capability of assimilating data from the ground to the top of the mesosphere (about 95 km). This model is a full general circulation model with on‐line fully interactive chemistry involving 127 gas‐phase and heterogeneous reactions. Thus, feedback between dynamics, chemistry and radiation occurs in every model time step. In this work, validation of the system for tropospheric and lower stratospheric analyses is undertaken with the standard observation set used in operational weather forecasting. Results are found to agree reasonably well with radiosonde observations and with Met Office (UK) analyses. Although ozone is not assimilated, ozone fields match total column observations well in terms of synoptic patterns. However, due to model biases, total column values are too large at mid‐latitudes and too small in the tropics. Since the assimilation scheme was designed for tropospheric weather prediction, its application to a middle atmosphere model can help to identify the challenges of assimilating data from this region of the atmosphere.

On the Relationship between Incremental Analysis Updating and Incremental Digital Filtering

Abstract Incremental analysis updating (IAU) refers to a method of smoothly inserting instantaneous analysis increments into a numerical model by spreading the increments over a time period. In this work, this method is shown to be identical to applying a digital filter to the time evolution of analysis increments [a method known as incremental digital filtering (IDF)] for the case of linear models with time-invariant coefficients. The equivalence of the two methods can be used to show that the constant weights typically employed in IAU applications result in too much damping of long waves. For weakly nonlinear models, the two methods will not produce identical filtered states even if the filter coefficients are the same. The implications of the similarities and differences of the two methods are discussed.

The stratospheric wind interferometer for transport studies (swift)

Abstract The Stratospheric Wind Interferometer For Transport studies (SWIFT) is an instrument intended to measure winds to an accuracy of 5 m s −1 or better in the stratosphere, during both day and night, as well as ozone concentrations. It is based on WINDII, the WIND Imaging Interferometer on the UARS satellite, but there are a number of important differences. WINDII operated in the visible region, with widely-spaced airglow emission lines, a field-widened Michelson interferometer that uses glass combinations to provide thermal stability, and a CCD detector. SWIFT uses the thermal emission from an ozone line near 8.9 μm, a region in which the choice of refractive materials is very limited. Through a careful search for a suitable line several were found of appropriate strength that were adequately isolated, but only with a combination of etalon filters. Fortunately, HgCdTe array detectors are available so the detector is not a problem. By measuring both winds and ozone concentration it is possible to measure ozone fluxes. SWIFT will study ozone transport, transport across the sub-tropical mixing barrier, equatorial dynamics and data assimilation. The latter is an important tool for the execution of the scientific objectives.

Satellite Measurement of Stratospheric Winds and Ozone Using Doppler Michelson Interferometry. Part I: Instrument Model and Measurement Simulation

Abstract This paper presents an instrument model and observation simulations for the measurement of stratospheric winds and ozone concentration using a satellite instrument employing imaging and the Doppler Michelson interferometery technique. The measurement technique and instrument concept are described. The instrument model and simulations are based on initial design characteristics of the Canadian Stratospheric Wind Interferometer for Transport Studies (SWIFT) satellite instrument. SWIFT employs an imaging array and a field-widened Michelson interferometer. It will measure stratospheric winds and ozone densities using the wind-induced phase shifts of interferograms from atmospheric limb radiance spectra in the vicinity of the vibration–rotation ozone line at 1133.4335 cm−1. The measurement simulation and analysis tools have been developed to assess the SWIFT instrument performance and to evaluate the impact of instrument and measurement characteristics on expected wind and ozone errors. Sample results...

Satellite Measurement of Stratospheric Winds and Ozone Using Doppler Michelson Interferometry. Part II: Retrieval Method and Expected Performance

Abstract This paper is about the retrieval of horizontal wind and ozone number density from measurement simulations for the Stratospheric Wind Interferometer for Transport Studies (SWIFT). This instrument relies on the concept of imaging Doppler Michelson interferometry applied to thermal infrared emission originating from the stratosphere. The instrument and measurement simulations are described in detail in the first of this series of two papers. In this second paper, a summary of the measurement simulations and a data retrieval method suited to these measurements are first presented. The inversion method consists of the maximum a posteriori solution approach with added differential regularization and, when required, iterations performed with the Gauss–Newton method. Inversion characterization and an error analysis have been performed. Retrieval noise estimates have been obtained both from derived covariance matrices and sample inversions. Retrieval noise levels for wind and ozone number density of ∼1–3...

Filters and calibration for the SWIFT instrument on GCOM-A1

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 NASDAs 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 NH3 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.

SWIFT: an infrared Doppler Michelson interferometer for measuring stratospheric winds

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 Earths 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 NASDAs GCOM-A1 satellite and a Phase A study is being supported by ESA and the Canadian Space Agency.

The Stratospheric Wind Interferometer For Transport studies (SWIFT)

The Stratospheric Wind Interferometer For Transport studies (SWIFT) is a Canadian satellite instrument designed to measure wind profiles between 20 and 45 km in the stratosphere with an accuracy of about 5 m s/sup -1/. It simultaneously provides co-located ozone density profiles with an accuracy of /spl sim/5%. SWIFT is a follow on to the highly successful WINDII instrument (WIND Imaging Interferometer) on the UARS satellite. WINDII measures winds in the upper mesosphere and lower thermosphere using Doppler shifts in visible airglow features. SWIFT will measure winds in the stratosphere using Doppler shifts of an ozone thermal emission line in the mid-IR region near 9 /spl mu/m. SWIFT has been selected by NASDA (the Japanese Space Agency) for deployment on their GCOM-A1 mission to be launched in early 2007. We describe the SWIFT science objectives, the SWIFT instrument concept, and SWIFTs synergies with the other instruments on NASDAs GCOM-A1 mission.