Odin is a 250 kg class satellite built in co-operation between Sweden, Canada, France, and Finland and launched in February 2001. It carries two instruments: a 4-band sub-millimetre radiometer used for both astronomy and atmospheric science and an optical spectrometer and infrared imaging system for purely atmospheric observations. As part of the joint mission Odin will observe the atmospheric limb for 50% of the observation time producing profiles of many species of interest in the middle atmosphere with a vertical resolution of 1–2 km. These species include, among others, ozone, nitrogen dioxide, chlorine monoxide, nitric acid, water vapour, and nitrous oxide. An overview of the mission and the planned measurements is given. PACS Nos.: 42.68Mj, 94.10Dy, 95.55Fw

The WIND imaging interferometer (WINDII) was launched on the Upper Atmosphere Research Satellite (UARS) on September 12, 1991. This joint project, sponsored by the Canadian Space Agency and the French Centre National d'Etudes Spatiales, in collaboration with NASA, has the responsibility of measuring the global wind pattern at the top of the altitude range covered by UARS. WINDII measures wind, temperature, and emission rate over the altitude range 80 to 300 km by using the visible region airglow emission from these altitudes as a target and employing optical Doppler interferometry to measure the small wavelength shifts of the narrow atomic and molecular airglow emission lines induced by the bulk velocity of the atmosphere carrying the emitting species. The instrument used is an all‐glass field‐widened achromatically and thermally compensated phase‐stepping Michelson interferometer, along with a bare CCD detector that images the airglow limb through the interferometer. A sequence of phase‐stepped images is processed to derive the wind velocity for two orthogonal view directions, yielding the vector horizontal wind. The process of data analysis, including the inversion of apparent quantities to vertical profiles, is described.

The optical spectrograph and infrared imager system (OSIRIS) on board the Odin spacecraft is designed to retrieve altitude profiles of terrestrial atmospheric minor species by observing limb-radiance profiles. The grating optical spectrograph (OS) obtains spectra of scattered sunlight over the range 280-800 nm with a spectral resolution of approximately 1 nm. The Odin spacecraft performs a repetitive vertical limb scan to sweep the OS 1 km vertical field of view over selected altitude ranges from approximately 10 to 100 km. The terrestrial absorption features that are superimposed on the scattered solar spectrum are monitored to derive the minor species altitude profiles. The spectrograph also detects the airglow, which can be used to study the mesosphere and lower thermosphere. The other part of OSIRIS is a three-channel infrared imager (IRI) that uses linear array detectors to image the vertical limb radiance over an altitude range of approximately 100 km. The IRI observes both scattered sunlight and the airglow emissions from the oxygen infrared atmospheric band at 1.27 µm and the OH (3-1) Meinel band at 1.53 µm. A tomographic inversion technique is used with a series of these vertical images to derive the two-dimensional distribution of the emissions within the orbit plane.Résumé : Le système de spectrographie optique et d'imagerie infrarouge (OSIRIS) à bord du satellite Odin est conçu pour enregistrer les profils en altitude des éléments mineurs de l'atmosphère en observant les profils de radiance du limbe. Le spectrographe optique à réseau (OS) obtient les spectres de la lumière solaire diffusée sur le domaine entre 280-800 nm, avec une résolution spatiale approximative de 1 nm. Le satellite Odin balaye verticalement le limbe de façon répétée, de telle sorte que l'ouverture verticale de 1 km du OS parcoure les domaines voulus entre 10 et 100 km. Nous analysons les spectres solaires diffusés en superposition avec les caractéristiques terrestres d'absorption, afin de déterminer les profils en altitude des éléments mineurs de l'atmosphère. Le spectrographe détecte aussi la luminescence nocturne atmosphérique qui peut être utilisé pour étudier la mésosphère et la thermosphère. L'autre partie d'OSIRIS est un imageur infrarouge (IRI) à trois canaux qui utilise une banque linéaire de détecteurs pour imager la radiance du limbe sur un domaine d'altitude d'approximativement 100 km. L'IRI observe à la fois la lumière solaire diffusée et les émissions de luminescence nocturne atmospérique provenant de la bande infrarouge de l'oxygène atmosphérique à 1.27 µm et la bande de Meinel de l'OH (3-1) à 1.53 µm. Nous utilisons une technique d'inversion tomographique avec une série de ces images verticales pour obtenir la distribution bidimensionnelle des émissions à l'intérieur de l'orbite.[Traduit par la Rédaction] Can.

Both Brewer and Dobson Spectrophotometers have been taking routine simultaneous direct‐Sun total ozone measurements from the five stations in the Canadian ozone monitoring network. The longest record of intercomparison data is at Toronto, where the well‐maintained Canadian regional standard Dobson instrument 77 is stationed and where routine ozone measurements made by Brewer instrument 8 commenced in February 1983. Results of this intercomparison are presented, and the causes for minor differences are discussed. A suitable transfer function is developed to calculate simulated Dobson ozone data from the Brewer data in order to ensure that the ozone record remains continuous and uninterrupted by the transition from the Dobson to the Brewer instrument. With appropriate corrections applied, the Dobson ozone values are 3.8% greater than those of the Brewer, and the standard deviation between the daily mean values is 0.5%. The relative drift between the two instruments over the 5‐year period was found to be 0.05% per year, smaller than the 95% confidence estimate of 0.27% per year.

Stratospheric ozone density profiles between 15 and 40 km altitude are derived from scattered sunlight limb radiance spectra measured with the Optical Spectrograph and InfraRed Imager System (OSIRIS) on the Odin satellite. The method is based on the analysis of limb radiance profiles in the centre and the wings of the Chappuis‐Wulf absorption bands of ozone. It employs a non‐linear Newtonian iteration version of Optimal Estimation (OE) coupled with the radiative transfer model LIMBTRAN. The derived zonally averaged ozone field for August 2001 is in excellent agreement with the main characteristics of the global morphology of stratospheric ozone, indicating that the limb scatter technique is capable of providing ozone profiles with high accuracy and high vertical resolution on a global scale and a daily basis.