Aladin: The First European Lidar in Space
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ALADIN: The First European LIDAR in Space
Didier Morançais and Frédéric Fabre EADS Astrium, 31 rue des cosmonautes 31402 Toulouse Cedex France, [email protected] ABSTRACT After several decades of observations from space, direct measurements of the global threedimensional wind field remain elusive, however crucial to weather predictions. The ALADIN instrument, payload of the AEOLUS satellite (figure 1), will provide measurements of atmospheric wind profiles with global Earth coverage for the climatology and meteorology users. The AEOLUS programme is sponsored by the European Space Agency with a launch planned in 2008. ALADIN belongs to a new class of Earth Observation payloads and will be the first European Lidar in space. The instrument comprises a diode-pumped high energy Nd:YAG laser and a direct detection receiver operating on aerosol and molecular backscatter signals in parallel. In addition to the Flight Model (FM), two instrument models are developed: a Pre-development Model (PDM) and an Opto-Structure-Thermal Model (OSTM). The OSTM integration has been completed and the flight equipments are under manufacturing. This paper describes the instrument design as well as the development status. The ALADIN instrument is developed under prime contractor EADS Astrium SAS with a consortium of thirty companies. THE MISSION ALADIN is a Doppler Lidar operating in the near ultra-violet spectral region using backscatter signals from aerosol at low altitude and from air molecules at high altitudes. Throughout its 3-year lifetime, ALADIN will produce more than 3 million wind profiles, each
Figure 1. Artist’s view of AEOLUS satellite © ESA
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one providing wind velocity from ground up to 30 km altitude. The wind profile vertical resolution is 500 m at low altitude and 2 km at the highest altitudes. The wind measurement accuracy is better than 1m/s in the Planetary Boundary Layer and better than 2 m/s in the Troposphere. The wind profile data will be processed and delivered in less than 3 hours after the measurements. The measurement principle is shown in figure 2. The satellite trajectory is a Low Earth Orbit at 400 km altitude with sub-satellite point motion around 7 km/s. The instrument points towards the Earth with a 35° slant angle versus the Nadir direction, oriented across-track. It measures the projection of the horizontal wind onto the inclined line-of-sight, for every altitude. In order to obtain high accuracy, 700 wind profiles are averaged during 7 seconds, which corresponds to a 50 km line on ground. This measurement is repeated every 28 seconds, which corresponds to every 200 km along the orbit.
Figure 2. Measurement principle
INSTRUMENT DESIGN AND PERFORMANCE The ALADIN instrument [1], [2] emits laser pulses towards the atmosphere and measures the Doppler shift of the return signal, backscattered from different altitudes in the atmosphere. The instrument emits the pulses at the 355 nm wavelength with a high power solid-state laser [3] featuring high efficiency and high reliabi
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