Computer Science – Sound
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.p33d..15b&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #P33D-15
Computer Science
Sound
3346 Planetary Meteorology (5445, 5739), 3394 Instruments And Techniques, 5409 Atmospheres: Structure And Dynamics, 5445 Meteorology (3346), 5494 Instruments And Techniques
Scientific paper
We are developing an acoustic anemometer for use in the low pressure atmosphere of Mars. Acoustic anemometers have high sensitivity, high temporal resolution, high accuracy, and are insensitive to radiative heating and demand little power. In these ways they are superior to the anemometers previously flown to Mars. Accurate, well-calibrated anemometers are crucial for understanding the near-surface atmospheric environment (e.g., slope winds, convective cells, dust devils, and aeolian processes in general). Furthermore, the high time-resolution, sensitivity, 3-D capabilities and well-defined, open sampling volume available from an acoustic anemometer allow it to resolve individual turbulent eddies, a first for Mars. This feature allows it to directly measure eddy fluxes, for example water vapor vertical fluxes between the surface and atmosphere when coupled with a fast hygrometer (e.g. a TDL). This novel ability to measure water vapor fluxes is viewed as a high priority science goal of Mars landers. We expect that the instrument designed in this program will be a prime candidate to fly on either the Mars Science Laboratory Lander (2009 launch), or any of the future planned Mars Scout landers or Mars Surveyor Landers. With adaptation, the instrument could also find application on Titan, or at high altitude on Earth. Acoustic anemometers are well developed for Earth, but need modifications to function in the vastly different martian pressure environment. The two main hurdles are sound attenuation in Mars air, and transducer coupling inefficiency from density and sound speed mismatches with Mars air. The sound attenuation on Mars is significant, especially at ultrasonic frequencies. We have a simple model of the relevant phenomena to guide our choices to the optimal frequencies for Mars. The coupling between a transducer and the atmosphere is characterized by the match of their densities and sound speeds, or acoustic impedances, similar to index of refraction in optics. The Martian atmosphere has an acoustic impedance of about 1% that of the Earth. The commonly used (on Earth) piezo transducers lose about 110dB coupling with Mars air. Matching plates are unsuitable due to bandwidth limitations. Acoustic horns may aid in matching impedances. Capacitive transducers have an inherently low acoustic impedance, and are now becoming available in the frequency ranges needed for Mars. We have secured 3 sources of cutting-edge capacitive transducers that are being tested in a simulated martian atmosphere anechoic chamber. Our testing and redesign is resulting in an optimized transducer for use on Mars. The goal of this project is to produce a proof-of-concept and functional design of an accurate, robust, versatile Martian anemometer with significantly greater capabilities than its predecessors.
Banfield Don
Dagle W. R.
Dissly Richard
Gierasch Peter J.
Hutchins D.
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