A new candidate mission for the Living Planet Programme
A new mission to measure stratospheric wind and ozone is currently being considered for implementation as part of ESA’s Living Planet Programme. The Stratospheric Wind Interferometer for Transport Studies (SWIFT) is a satellite instrument designed to measure wind profiles in the stratosphere and will simultaneously provide profiles of ozone density. This mission is aimed at furthering our knowledge of atmospheric circulation and will help us understand how pollutants are transported within the atmosphere and explain the way in which ozone is distributed in the stratosphere.
SWIFT was originally proposed as an Earth Explorer Opportunity Mission in 1998, it was however, in competition with other excellent proposals and higher priority was given to the Soil Moisture Ocean Salinity (SMOS) and CryoSat missions, which are currently being developed. Nevertheless, because of the importance of the mission, SWIFT was proposed by ESA to the National Space Development Agency of Japan (NASDA), as a third-party payload on the Japanese GCOM-A1 satellite. Out of a number of proposals received by NASDA, SWIFT was selected. Since the other instrumentation to be carried on GCOM-A1 will measure the chemical composition of the atmosphere, the scientific goals of SWIFT complement the payload on the Japanese satellite very well. In cooperation with the Canadian Space Agency (CSA), which supports the development of the SWIFT instrument, ESA performed a feasibility study (Phase A) for SWIFT on-board GCOM-A1. Phase- A has now been successfully completed and pending GCOM-A1 mission approval by the Japanese government and approval for SWIFT implementation by ESA’s Programme Board for Earth Observation, SWIFT will be launched on GCOM-A1 in 2007.
SWIFT is aimed at providing much needed information about global wind distributions in the stratosphere by measuring the thermal emission of ozone molecules in the infrared at a wavelength of 9 micrometer. Because ozone molecules are moved in the atmosphere by the wind, the wavelength of their emission line appears to be shifted when measured by the so called Doppler effect. SWIFT is able to measure this tiny wavelength shift with high accuracy and consequently stratospheric wind can be calculated. Although this concept has already been successfully employed for wind measurements in the mesosphere (the atmospheric layer above the stratosphere) with the Canadian WINDII instrument, this is the first time that this technique will have been used to take direct stratospheric wind measurements from space. Since SWIFT will observe an ozone emission line, it will also be able to measure ozone concentration simultaneously with the wind and as such will offer further possibilities for ozone transport studies.
Increasing our knowledge of wind measurements in the stratosphere is important because this will further our understanding of how pollutants are transported in the atmosphere. Stratospheric ozone has been significantly depleted due to man-made pollution over the last few decades. However, despite the general downward trend in stratospheric ozone there are still many uncertainties regarding ozone distributions and depletion events. Ozone concentration and distribution is not only based on chemical reactions but is also greatly affected by the movement of air in the stratosphere. A good knowledge of the dynamics in the stratosphere and troposphere is indispensable for the correct scientific interpretation of observed ozone distributions.
The field of meteorological science and observation has provided us with very good tools to quantify the dynamics of the troposphere, in fact ESA is set to contribute further to this area of study with the launch of ADM-Aeolus in 2007. Meteorological models and measurements also extend significantly into the stratosphere and state-of-the-art satellite observations provide global information on almost all relevant parameters, however with one exception – wind. The objective of the SWIFT mission is to fill this gap. SWIFT will also provide an important opportunity for ESA to work in cooperation with the Japanese and Canadian space agencies and scientists.