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ADM-Aeolus  Aeolus mission payload
A lidar uses the phenomenon of light scattering and the Doppler Effect to acquire data on wind. A lidar works by emitting a short, but powerful, light pulse from a laser through the atmosphere and then collects light that is backscattered from particles of gas and dust and droplets of water in the atmosphere. The time between sending the light pulse and receiving the signal back determines the distance to the ‘scatterers’ and thus the altitude above Earth. As the scattering particles are moving in the wind, the wavelength of the scattered light is shifted by a small about as a function of speed. The Doppler wind lidar measures this change so that the velocity of the wind can be determined.
So the Aeolus instrument, the Atmospheric Laser Doppler Instrument, or Aladin for short, comprises a powerful laser, a large telescope and a very sensitive receiver.
The laser is actually a complex system of laser sources and amplifiers, which are all packaged closely together. There are two small lasers to fix the frequency of the emitted pulses, a laser oscillator to generate pulses and two amplifier stages that boost the energy of the light pulses to the required value.
The receiver analyses the Doppler shift of the backscattered signal with respect to the frequency of the transmitted laser pulse. Two optical analysers measure the Doppler shift of the molecular scattering, ‘Rayleigh’, and scattering from aerosols and water droplets, ‘Mie’.
Highly sensitive photo-detectors then transform the light signals into electronic signals. The wind profiles are accumulated over at least 20 individual measurements before being downlinked to ground for further averaging. The typical averaging distance is 90 km, corresponding to 12 seconds.
Last update: 19 January 2012
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