Page 15 - Spring 2019
P. 15

l _ oo.m.,»-
.4’ \.
. ‘ came dormant after the invention of radar in the 19305. The
Australian Armys idea was that the signal-processing tecl1-
V T” i 7” niques developed for the hydrophones of a submarine be
(:1 m_. i C10": i r”; i used for microphones deployed on the battlefield. The goal
A ” R = j{(n _ in) was "low-cost intelligent acoustic-sensing nodes operating
3......“ 2 .
i * I My 3 on shoestring power budgets for years at a time in potentially
K "l 7i, I l H hostile environments without hope of human intervention”
‘ (Hill et al., 1004).
Figure 4. Lghuehemaxieshawingzhesaam-sehsmeanfigumxianfm The swing Dfsmmd on the bmiefieid makes sense because
passive ranging by 11 wavefront curvatme. Right: E7055-Cflrifllatlml ti _ i
functions for the outputs ufsznsars 1,2 and sensors 2,5. 7he lime ‘*°°“S C 55550“ i“=_P=*S_51V8- _ _ _ _
lags corresponding to the peaks in the two cross-correlogmrris pm- - sound propagation is not lmmed by line of sight;
vidz estimates of rhe time delays rig and -rm . These time delays are - the false-alarm rate is negligible due to smart signal
substituted into the passive ranging equation to calculate the range i,,-messing;
(R). q Speed afsound traveling in the underwater medium; d, in- _ ii d Ci ii -iii iii » - ii i ii ai
 separation  Fram  and am, (2001). ;-;;i;;;m;fw=;:i,‘;jh:fii V;;m;;;“;;g wgjnfmcmi
to a central monitoring facility;
ad]-“mi pairs ofsmsms mabies esiimation ofihe source range - sensors are light weight, low cost, compact, and robust;
from the middle any and ii“ source bearing with respeci to - acoustic systems can cue other systems such as a cameras,
the longitudinal axis of the wide-aperture array. Measuring a "dam:  weapons; _ _
time delay involves cross-correlating the receiver outputs. The ' aC°_“SllC slgnalines °l all  gmlmd Vel“C_les enable
time delay corresponds to the time lag at which the cross-cor- "Pm classlfillal-la“ °fl}"Pe “fa” °l' gmllllll V°lllCl° 35 Well
relation function attains its maximum value. ‘5 w‘‘P°ll file‘ 35'-l
- military activities are inherently noisy.
Figure 4, right. shows the cross-correlation functions for The submarine aiipmach io widefiiea surveillance requires
sensor Pal” 1’2 and L3‘ In pmcllc°' “lays ofseumls ("lllel arrays with large numbers of closely spaced sensors (subma-
l-lliall llleisl-“file 53ll5°l'5 5l1°Wn he”) ETC “Sad (0 Pmvlde “RY rines bristle with sensors) and the central processing of the
33”» ll l5 llle l’“mf°”lle‘l °“lP“l5 ‘llal 7*” ‘7l'°55'“°"°lal' acoustic sound field information on board the submarine. In
all l° llllPl'°Ve ll“ e5lll'l“le5 °f ll“ llme ‘l"l3Y5‘ Each ‘"37’ contrast, wide-area surveillance of the battlefield is achieved
5al'l'lPl55 ll“ llllclerwalel ‘°“ll‘l llelll f°l' 20 5* ‘hen ll” ‘°l'll' by dispersing acoustic sensor nodes throughout the surveil-
plex weights are calculated so that an adaptive beamformer lance area, iiieii networking (hem and using decenifliizfid
maxlllllzes the al'l'3Y Balm 5llPPle55°5 sldz l°l’e5' and ‘um’ data fusion to compile the situational awareness picture. On
mallcalli’ steels nulls ll‘ the dlflctlolls °f l“lel_fele“Ce' _-l-he the battlefield, only a minimal number of sensors (often, just
Pl'°‘°55 l5 l'ePe“l“l “Very 20 5 llzullsz llle lelallve “°l'lll'll’“' one) is required for an acoustic-sensing node to extract the
tions of the signal. noise, and interference components to the iaciicai iii‘-oimaiian (imsiiiim Speed range ai ihe Ciosesi
llll‘l€l'W3l9l' 5°“l'l‘l field call Val)’ °Vel' 3 P"l°Cl °fmll'l“le5‘ ll‘ point of approach to the sensor) of a contact and to classify
5“lllm3l'Y- l’e3mf°ll'llll'lS and Plellllfllllg 5“Pl’l'e55 e"llalle' it. For example in 2014 the Acoustical Society of America
0‘-'5 Peal“ Wlllcll 59”“ ll’ lllgllllglll ‘he Peal‘ aS5°°l“Ed Wllll (ASA) Technical Committee on Signal Processing in Acous-
a c°lll“Cl (F"g“s°n’ 199%)‘ tics posed an international student challenge problem (avail-
able at lr_iN3AG) where the students were given a 30-s
Batfiafiald Acoustics sound file of a truck traveling past a microphone (Ferguson
Extracting Tactical lnfizrmatian with a Microphone and Culver, 2014). By processing the sound file, the students
In 1995, sonar system research support to the Royal Aus- were required to extract the tactical information so that they
tralian Navy Oberon Submarine Squadron was concluded, could respond to the following questions,
which ushered in a new research and development program - What is the speedometer reading?
for the Australian Army on the use of acoustics on the battle- - What is the tachometer reading?
field. Battlefield acoustics had gone out of fashion and be- - How many cylinders does the engine have?
Spring 2019 | An:nulI:lI:l Thday | 13

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