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Figure 2. Variation with frequency and apparent bearing of the output power of a line array of hydrophones. Prominent sources of acoustic energy are labeled. After Ferguson and Speechley (1989).
at 44.1 kHz for 2 minutes, during which time a turboprop aircraft passes overhead. The sampled data are recorded in Waveform Audio File format (WAV) with the file name Hy- drophone Output Time Series, which can be downloaded at the above URL. The students are invited to estimate the speed of the aircraft (in meters/second), the altitude of the aircraft (in meters), the source (or rest) frequency (in hertz), and the time (in seconds) at which the aircraft is at its closest point of approach to the hydrophone (i.e., when the source is directly above the sensor).
The deadline for student submissions is September 30, 2019, with the finalists and prize winners (monetary prizes: first place $500; second $300; third $200) being announced at the 178th meeting of the Acoustical Society of America in San Diego, CA, from November 30 to December 4, 2019.
Figure 3. Direct refraction acoustic ray path and mathematical descriptions of the Doppler frequency (fd) , where fs is the source frequency, vs is the source speed, ξ is the elevation angle of the refracted ray, γ is the depression angle of the incident ray, and ca and cw are the speed of sound travel in air and water, respectively. The Doppler frequency and elevation angle are unique to each individual acoustic ray. After Ferguson and Speechley (1989).
References
Dall’Osto, D. R., and Dahl, P. H. (2015). Using vector sensors to measure the complex acoustic intensity field. The Journal of the Acoustical Society of America 138, 1767.
Ferguson, B. G., and Culver, R. L. (2014). International student challenge problem in acoustic signal processing. Acoustics Today, 10 (2), 26-29.
Ferguson, B. G., and Speechley, G. C. (1989). Acoustic detection and local- ization of an ASW aircraft by a submarine. The United States Navy Journal of Underwater Acoustics 39, 25-41.
Urick, R. J. (1972). Noise signature of an aircraft in level flight over a hydrophone in the sea. The Journal of the Acoustical Society of America 52, 993-999.
Planning Reading Material for
Your Classroom?
Acoustics Today (acousticstoday.org) contains
a wealth of excellent articles on a wide range of topics in acoustics.
All articles are open access so your students can read online or download at no cost. And point your students to AT when they're doing research papers!
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