Acoustic Measurements on the Huygens Probe and Other Platforms: A Review
Lorenz, Ralph D.
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The Huygens probe at Titan recorded broadband sound levels during descent and on the surface with a passive microphone processed with a spectrum analyzer (part of the HASI experiment) as well as an active acoustic sounder (part of the SSP experiment). Some preliminary results of the SSP sounder near the surface have been reported previously : the present work examines data acquired during the descent and the light it may shed on atmospheric turbulence and possible precipitation. A major feature of any planetary acoustic measurement is noise due to ambient winds, or to the motion of the measurement platform through the air. Venera 13 and 14 recorded sound on the surface of Venus : the amplitude of the microphone signal was interpreted (by dynamic pressure scaling) to recover a windspeed. The Huygens SSP and HASI data are examined from this perspective. The paper will also review passive microphone measurements made on a rotating aerospace vehicle (an instrumented Frisbee) which show spin modulation and a variation with flight speed and angle of attack. The author has also used microphones as a crude wind sensor on an array of 20 meteorological stations to study dust devils in Arizona. Lessons learned and prospects and methods for microphonic anemometry (especially with limited telemetry bandwidth) on future missions will be discussed.