The Atmospheric Limb Sounding Satellite (ALISS) is a joint Canadian-Swedish concept that is currently under study by agencies, industrial partners and academic institutions in both countries. Launch is not anticipated before late 2020. ALISS has significant heritage, resembling the current Odin mission in terms of some of the countries involved and the types of instruments. However, ALISS will have a focus on the upper troposphere in addition to Odin's primarily stratospheric focus. The ALISS mission has objectives relating to climate-chemistry coupling, UV radiation, dynamics, atmospheric composition in the upper troposphere and lower stratosphere, and in conjunction with nadir sensors, air quality, by virtue of the array of key atmospheric constituents that it will measure with an unprecedented combination of vertical and horizontal resolution for satellite-borne instruments. ALISS consists of four atmospheric limb remote sensing instruments. Three of these have space heritage and are: the Canadian-designed Atmospheric Tomography System (CATS) that is a derivative of the highly successful Optical Spectrograph and InfraRed Imaging System (OSIRIS) instrument, the Swedish-designed Stratosphere Troposphere Exchange And climate Monitoring Radiometer (STEAMR) that is a follow-on instrument to the sub-millimetre radiometer (SMR) that currently operates with OSIRIS on Odin, and a Global Positioning System Radio Occultation instrument. The fourth instrument, also Canadian, is the Spatial Heterodyne Observations of Water (SHOW). SHOW will measure profiles of water vapour using its near-infrared absorption. Among other things, the ALISS package will deliver atmospheric composition (O 3 , H 2 O, NO 2 , HNO 3 , BrO, CO, aerosol, and others) measurements within the extremely important upper troposphere and lower stratosphere region for chemistry and climate studies. One application of interest would be using these measurements in conjunction with total column measurements from nadir-viewing instruments as well as data assimilation systems in order to better monitor and forecast air quality. Also, the heritage of these instruments implies the ALISS measurements will be extremely valuable in the continuation of climate-quality time series of important constituents such as stratospheric aerosols, water vapour, and ozone. Continuity of these vertically resolved data records is currently threatened by a looming gap in satellite-based limb sounders. This talk will outline the ALISS concept and the utility of the measurements.

Three independent small Mars Mission concepts had been developed in Finland, Sweden and Germany. The high degree of commonality resulted in a unified small mission concept for a combined orbiter and lander mission which will carry an overall payload mass of up to 60 kg including the lander to Mars. The baseline scenario is a launch in 2011. Two different alternatives have been analyzed with a launch by Ariane ASAP 5 and a direct injection into Mars transfer orbit by a small dedicated launcher (Rockot). A trade-off between the different scenarios favors the direct launch which reduces the overall mission duration and complexity and would provide more volume. The key objective of the mission is to perform simultaneous measurements from the orbit and on ground of the Martian atmosphere, the magnetic field, and the radiation environment. The orbiter payload with an overall mass up to 30 kg consists of a magnetometer, a camera instrument, a microwave sounder, a plasma package, and a dosimeter. The telecommunication system is equipped with an ultra-stable oscillator for radio science investigations. The orbiter experiments thus combine new atmospheric science, detailed geophysical and surface observations, and measurements of the space environment around Mars, something that will not be provided by any other present or planned mission. A small landing device is foreseen to carry payloads down to the Martian ground for in-situ measurements of the Martian environment and its lower atmosphere. The baseline payload package consists of sensors to measure the magnetic field, charged particles and UV radiation, and thermal radiation. A suite of atmospheric sensors shall measure pressure, temperature, humidity, wind and atmospheric optical depth. A small panoramic camera will image the surrounding landing site. The landing device weighs about 30 kg overall including the entry, descent and landing systems and would serve as a technical demonstrator for several phases in landing.

In September 2002 the Antarctic polar vortex split in two under the influence of a sudden warming. During this event, the Odin satellite was able to measure both ozone (O3) and chlorine monoxide (ClO), a key constituent responsible for the so‐called “ozone hole”, together with nitrous oxide (N2O), a dynamical tracer, and nitric acid (HNO3) and nitrogen dioxide (NO2), tracers of denitrification. The submillimeter radiometer (SMR) microwave instrument and the Optical Spectrograph and Infrared Imager System (OSIRIS) UV‐visible light spectrometer (VIS) and IR instrument on board Odin have sounded the polar vortex during three different periods: before (19–20 September), during (24–25 September), and after (1–2 and 4–5 October) the vortex split. Odin observations coupled with the Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) chemical transport model at and above 500 K isentropic surfaces (heights above 18 km) reveal that on 19–20 September the Antarctic vortex was dynamically stable and chemically nominal: denitrified, with a nearly complete chlorine activation, and a 70% O3 loss at 500 K. On 25–26 September the unusual morphology of the vortex is monitored by the N2O observations. The measured ClO decay is consistent with other observations performed in 2002 and in the past. The vortex split episode is followed by a nearly complete deactivation of the ClO radicals on 1–2 October, leading to the end of the chemical O3 loss, while HNO3 and NO2 fields start increasing. This acceleration of the chlorine deactivation results from the warming of the Antarctic vortex in 2002, putting an early end to the polar stratospheric cloud season. The model simulation suggests that the vortex elongation toward regions of strong solar irradiance also favored the rapid reformation of ClONO2. The observed dynamical and chemical evolution of the 2002 polar vortex is qualitatively well reproduced by REPROBUS. Quantitative differences are mainly attributable to the too weak amounts of HNO3 in the model, which do not produce enough NO2 in presence of sunlight to deactivate chlorine as fast as observed by Odin.

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. PACS Nos.: 07.05.Pj, 07.60.Dq, 07.60.Rd, 07.87, 94.10.Dy, 94.10.Fa, 94.10.Gb, 94.10.Rk

Observations of the Earth's atmosphere are sharing time with astronomy observations on the Odin satellite. Many scientists from both scientific disciplines are now using data collected by Odin since its successful launch in 2001. The Swedish Space Corporation (SSC) developed the Odin system and is also responsible for the operations. The complex mission features a mix of extreme high-technology development, simplified system design and operations, all in a low-cost approach and in a framework of international collaboration between four countries.The small dedicated team responsible for design, development and operations, the simple and open customer and end-user interfaces are some keys to the quality and low-cost achieved. Technical and managerial factors contributing to lower risk/higher quality/lower cost - and vice versa - are discussed in the paper. Conclusions are drawn for a follow-on climate research mission, STEAM. (C) 2003 Elsevier Science Ltd. All rights reserved.

Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (J(K) = 1(0) --> 0(0)). The interpretation of this result makes use of complementary molecular line data obtained from the ground ((CO)-O-17 and CH3OH) as part of the Odin preparatory work. Comparison of these observations with theoretical model calculations of line excitation and transfer yields a quite ordinary abundance of methanol, X(CH3OH) = 3 X 10(-9). Unless NH3 is not entirely segregated from (CO)-O-17 and CH3OH, ammonia is found to be significantly underabundant with respect to typical dense core values, viz. X(NH3) = 8 X 10(-10).

Key Odin operational and instrumental features and highlights from our sub-millimetre and millimetre wave observations of H2O, (H2O)-O-18, NH3, (NH3)-N-15 and O-2 are presented, with some insights into accompanying Odin Letters in this A& A issue. We focus on new results where Odin's high angular resolution, high frequency resolution, large spectrometer bandwidths, high sensitivity or/and frequency tuning capability are crucial: H2O mapping of the Orion KL, W3, DR21, S 140 regions, and four comets; H2O observations of Galactic Centre sources, of shock enhanced H2O towards the SNR IC443, and of the candidate infall source IRAS 16293-2422; (H2O)-O-18 detections in Orion KL and in comet Ikeya-Zhang; sub-mm detections of NH3 in Orion KL (outflow, ambient cloud and bar) and rho Oph, and very recently, of (NH3)-N-15 in Orion KL. Simultaneous sensitive searches for the 119 GHz line of O-2 have resulted in very low abundance limits, which are difficult to accomodate in chemical models. We also demonstrate, by means of a quantitative comparison of Orion KL H2O results, that the Odin and SWAS observational data sets are very consistently calibrated.

Odin is a satellite with a combined astronomy and aeronomy mission. It is designed for observations of species difficult or impossible to observe from ground, especially water and oxygen. The main instrument is a radiometer, operating in the frequency range 486 - 581 GHz and at 118.75 GHz. Its double-reflector telescope has a 1.1 m primary and the front-end amplifiers are cooled for maximum sensitivity. A 3-axis-stabilisation system provides a pointing accuracy better than 10". Odin was developed on behalf of the space agencies in Sweden, Canada, France and Finland and was launched into a sun synchronous circular orbit in February 2001. The Odin Science Team, composed of astronomers and aeronomers from the partner countries, has established the observing programme and is responsible for all scientific matters regarding the Odin project. The spacecraft and instruments are performing well and operations are expected to continue well beyond the nominal two-year lifetime.

The Odin satellite, which can observe the 1(10)-1(01) rotational line at 557 GHz of ortho water with a high spectral resolution (80 m s(-1)) and a spatial resolution of 2.1', is well suited for cometary studies. The intensity of this line provides an estimate of the water production rate. The line width gives a direct measure of the coma expansion velocity. The line centre position and shape are affected by the anisotropy of the outgassing and by optical depth effects. Comets observed with Odin up to now are C/2001 A2 (LINEAR) during the commissioning phase of the satellite, 19P/Borrelly at the time of the Deep Space 1 flyby, C/2000 WM1 (LINEAR), and 153P/2002 C1 (Ikeya-Zhang). For this last comet, thorough observations were made at the moment of its closest approach to Earth at the end of April 2002. A deep integration resulted in the detection of the 1(10)-1(01) line of (H2O)-O-18 at 548 GHz. No O-16/O-18 isotopic anomaly is found.

New results from water mapping observations of the Orion KL region using the submm/mm wave satellite Odin (2.1' beam size at 557 GHz), are presented. The ortho-H2O J(K+K-) = 1(1,0) --> 1(0,1) ground state transition was observed in a 7' x 7' rectangular grid with a spacing of 1', while the same line of (H2O)-O-18 was measured in two positions, Orion KL itself and 2' south of Orion KL. In the main water species, the KL molecular outflow is largely resolved from the ambient cloud and it is found to have an extension of 60"- 110". The H2O outflow profile exhibits a rather striking absorption-like asymmetry at the line centre. Self-absorption in the near ( or "blue") part of the outflow ( and possibly in foreground quiescent halo gas) is tentatively suggested to play a role here. We argue that the dominant part of the KL (H2O)-O-18 outflow emission emanates from the compact (size similar to 15") low-velocity flow and here estimate an H2O abundance of circa 10(-5) compared to all H-2 in the flow - an order of magnitude below earlier estimates of the H2O abundance in the shocked gas of the high-velocity flow. The narrow ambient cloud lines show weak velocity trends, both in the N-S and E-W directions. (H2O)-O-18 is detected for the first time in the southern position at a level of similar to 0.15 K and we here estimate an H2O abundance of (1 - 8) X 10(-8).

Using the Odin satellite, we have mapped the submillimeter emission from the 1(10)-1(01) transition of ortho-water in the W3 star-forming region. A 5' X 5' map of the W3 IRS4 and W3 IRS5 region reveals strong water lines at half the positions in the map. The relative strength of the Odin lines compared to previous observations by SWAS suggests that we are seeing water emission from an extended region. Across much of the map the lines are double-peaked, with an absorption feature at 39 km s(-1); however, some positions in the map show a single strong line at -43 km s(-1). We interpret the double-peaked lines as arising from optically thick, self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted lines originate in emission near W3 IRS4. In this model, the unusual appearance of the spectral lines across the map results from a coincidental agreement in velocity between the emission near W3 IRS4 and the blue peak of the more complex lines near W3 IRS5. The strength of the water lines near W3 IRS4 suggests we may be seeing water emission enhanced in a photon-dominated region.

Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (JK = 10 -> 00). The interpretation of this result makes use of compleme ...

The Odin satellite has been used to detect emission and absorption in the 557-GHz H2O line in the Galactic Centre towards the Sgr A* Circumnuclear Disk (CND), and the Sgr A +20 km/s and +50 km/s molecular clouds. Strong broad H2O emission lines have been detected in all three objects. Narrow H2O absorption lines are present at all three positions and originate along the lines of sight in the 3-kpc Spiral Arm, the -30 km/s Spiral Arm and the Local Sgr Spiral Arm. Broad H2O absorption lines near -130 km/s are also observed, originating in the Expanding Molecular Ring. A new molecular feature (the “High Positive Velocity Gas” - HPVG) has been identified in the positive velocity range of +120 to +220 km/s, seen definitely in absorption against the stronger dust continuum emission from the +20 km/s and +50 km/s clouds and possibly in emission towards the position of Sgr A* CND. The 548-GHz H2_18O isotope line towards the CND is not detected at the 0.02 K (rms) level.

Odin has successfully observed three regions in the OrionA cloud, i.e. OriKL, Ori S and the Orion Bar, in the 572.5 GHz rotational ground state line of ammonia, ortho-NH3 (J; K) = ( 1; 0) --> (0; 0), and the result for the Orion Bar represents the first detection in an ammonia line. Several velocity components are present in the data. Specifically, the observed line profile from the Orion Bar can be decomposed into two components, which are in agreement with observations in high-J CO lines by Wilson et al. (2001). Using the source model for the Orion Bar by these authors, our Odin observation implies a total ammonia abundance of NH3/H-2 = 5 X 10(-9).

This paper describes the development of the Swedish Small Satellite Programme. These satellites have delivered excellent scientific data at a low cost by using streamlined project organisations, competitive procurement programmes and piggy-back launch opportunities.