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Figure 2. Variation with frequency and apparent bearing of ‘ 5 ‘W
the output power ofa line array ofhydrophones. Prominent
“"7595 ‘if “‘”“5”‘ ‘”"X}’ We l“l7eled‘ Aft" Fe’g“5’’” “"1 Figure 3. Direct refraction acoustic ray path and mathematical
SP“‘hl‘}' (1989) descriptions of the Doppler frequency (fd), where f is the source
ﬁequency, V‘ is the source speed, E is the elevation angle of the
td,'thd' th"dt,d
at 44.1 kHz for 2 minutes, during which tune a turboprop mfmc 6 my Y is e epyessum angle Dif 2 mm M my all C“
. _ and c are the speed of sound travel in air and water, respectively.
aircraft passes overhead. The sampled data are recorded in The [:0 I”/,re um and elevation angle We “mi 1“ to each
Waveform Audio File format (WAV) with the ﬁle name Hy- _ _ _ PP q_ L7 [1
dmphone Omput Time Series) which can be downloaded individual acoustic ray. After Ferguson and Speechley (1989).
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
. . . ’ sto, . ., an a , . . . sing vector sensors to measure
Pfm“ °f “PP'°“Ch ‘° '1” hyd’°Ph°"e (‘"6" when the mum L‘ the complex acoustic intensity ﬁeld. The Iournal ojthc Acoustical Society of
directly above the sensor). Ammm 138, 1761
F ,3. G., d Cul ,R. L. (2014). rm 1‘ al st d \ hall
The deadline for student submissions is September 30, 2019,  an acnuaslljc §ign::rp[0cg§5ing_ Am,.;;::;,E:y, 1au(2:,nz5c.z9_enge
with the ﬁnalists and prize winners (monetary prizes: first Ferguson, B. G., and Speechley, G. C. (1989). Acoustic detection and local-
place \$500; second \$300; third \$200) being announced at the ::::l:*;_:“3‘;l2’5’:rbm"‘"°- Th‘? 17""-‘3‘l SW” NW! l°’“"‘“l
178th meeting of the Acoustical Society of America in San UmkR_]_(1972)_N0i5e5igm’mm Df;1naimmﬂinlevelﬂw1‘0Vem}‘YdmPhom
Diego, CA, from November 30 to December 4. 2019. inthe sea. The Iuumal uflhe Acoustical Society o]America 52, 993-999.
/,,.—  Material for
7. r—  Acoustics Today (acousticstoday.org) contains
‘ 2 . : T a wealth of excellent articles on a wide range of
I topics in acoustics.
: f3 All articles are open access so your students can read
5' ' ‘ “ , ‘9 toATwhen they're doing research papers!
Spring 2019 | Annuslzlcl Tnduy | 13

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