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Martian Sonic Anemometer

Martian Sonic Anemometer. D. Banfield (PI - Cornell) R. Dissly (Ball Aerospace) M. Richardson, I. McEwan (CIT) D. Schindel (MicroAcoustics). Measures wind speed via sound pulse travel-time differences. Temperature is inferred from sound speed. How to Improve Martian Wind Measurements?.

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Martian Sonic Anemometer

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  1. Martian Sonic Anemometer • D. Banfield (PI - Cornell) • R. Dissly (Ball Aerospace) • M. Richardson, I. McEwan (CIT) • D. Schindel (MicroAcoustics)

  2. Measures wind speed via sound pulse travel-time differences. Temperature is inferred from sound speed. How to Improve Martian Wind Measurements? • Adapt premier terrestrial technique for Mars: Sonic Anemometry Terrestrial Research-Grade Sonic Anemometer

  3. Sonic Anemometry Advantages • 3-D capable (open sensing volume) • Higher sensitivity (<5 cm/s) • Higher time resolution (10-100 Hz) • Also yields temperature! (<0.2K) • OR if T provided, yields γR*/m • Improved accuracy (fewer biases) • e.g., Insensitivity to radiative heating • Resolve eddies, measure fluxes (heat, momentum, water vapor)

  4. Why Are These Capabilities Important? • Opens up Boundary Layer studies • e.g., Test Businger-Dyer relation @ Mars! • Directly measure fluxes • Heat flux for surface energy balance • Momentum flux for aeolian processes • Water vapor flux for water stability/climate • Provide more robust measures for model validation • U, V, T, P alone aren’t enough to validate mesoscale models adequately • Fluxes give more dimensions to compare models to data • Improved models mean safer S/C delivery • Hunt critters tracking bio-tracer effluents? • Earth animals use this (hunting lobsters, mating moths)

  5. Development History • PIDDP funding from ‘02-’06 • Proof of concept up through breadboard • Chamber tested to function @ <~4mbar CO2, -30C • Transducer miniaturization • Signal Processing algorithms explored • Stratospheric balloon flight attempted

  6. Development Challenges CO2 attenuates high frequencies • High frequencies critical for precise timing • Answers: • Broadband transducers • Good signal processing • -e.g., Pulse compression (from radar), spread spectrum (cell phones), Kalman Filtering From Williams (2000)

  7. Development Challenges Emitting/Receiving Sound in 6 mbar CO2 • Low atm density means poor transducer coupling • Acoustic impedance mismatch using piezoelectric devices in low pressure medium • Answer is to useappropriate transducers: Capacitive micro-machined devices

  8. Metal contact (fixed backplate) Metal contact (movable) Silicon nitride membrane Etch Holes Air cavity Insulator Substrate 1mm Capacitive Transducers

  9. Capacitive Transducers Developed new Miniature Transducers for Anemometer Use • 1.1cm diameter X 0.7cm depth

  10. Stratospheric Balloon Testing

  11. Notional System for Flux Measurements Combine with TDL hygrometer for water flux • TDL Hygrometer adds about 500g, 256cm3 • Sensitivity of 0.1ppmv at 10 Hz (Webster, personal comm.) • Should be sufficient for measuring typical Martian water vapor regolith/atmospheric exchange in real time

  12. Martian Sonic Anemometer • Technical Characteristics: • Mass: 950 g • Volume: Total: 1500 cm3 • electronics: 1000 cm3 • Sensor Head: D=15 cm sphere deployed D=15 cm X 3 cm deep cylinder stowed • Power: <10 W active, 0 W quiescent • On-time: instantaneous • Maximum Data Rate: 1200 Byte/s • Typical Data Rate: 80 Byte/s • Typical observing scenario: 2 min every 2 hours => 4 W-hr/day & ~0.1 MB/day • Key Performance Characteristics: • Measurement Rate: <100 Hz • Wind Speed Accuracy: ~<5 cm/s • Temperature Accuracy: 0.2 K • Fluxes (horizontal and vertical; heat, momentum, water vapor?)

  13. Acoustic anemometer measures wind via sound pulse travel-time differences. Temperature is measured from average travel times. Scout Sonic Anemometer • PI- Don Banfield (Cornell) • The Mars Sonic Anemometer uses earth-proven techniques with Mars-specific micro-machined acoustic transducers. • Measures 3-D wind vector and co-located temperature, and resolves turbulent eddies. • 3-D measurement means deployment insensitive. • Combined with TDL hygrometer, can return water vapor flux; but alone can still return heat and momentum fluxes Deployable Mast Sensor Array (15 x 15 x 3cm stowed) Electronics Box

  14. Status and Future Work • Currently TRL~4 for system • PIDDP funding from ’09-’11 • Transducer optimization • Tune for typical s/c voltage operation • Transducer environmental validation • Test at LOW temps & high thermal cycling • Test under dust impact exposure • Electronics miniaturization/optimization • Flight-like electronics • Field/Wind Tunnel/Stratospheric Balloon Testing • Test against terrestrial standards • Test at Ames MARSWIT • Test on Stratospheric Balloon

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