Page 17 - Spring 2019
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la?‘ . detach palnl I’,, fl priézlscimry
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,i poinwave
me ’
muzzle blast sensor
2. Atom: mnslenulamls- muzzle hlasuuierued It
me win in are; balllnle shock wave «Ilium: mm
me «man palm .-mum nuilm mlmarv
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Figure 5. Top: Izfi, image sliawing tlie caniml wave frnnt af the ballistic snack wave at Vuriaus detach paints alang the trujectmy nfthe su-
perszmic bullet; right, saaieesensai genmetry anal bullet trajectnry. Bottom: Izfi, saurce afsmall urms fire; right, “N"—sliapeal wave/arms af
ballistic shack waves far increasing miss distances. Pram Ferguswl et al. (2007).

Detecting the muzzle blast signals and measuring the time is achieved with an investment many times less than the cost
difference of arrival (time delay) of the wave front at a pair of of mirie-clearing operations.

spatially separated sensors providesan esti.rnate of the source Once a mine like object (MLO) is detected by a high_fi_e_
direction. The addition of another sensor forms a wide aper- quency (N100 kHz) mine_huming mm“ the next step is to
ture array configuration of three widely spaced collinear sen- identify it The safest way to do this is 18’ image the mine at
sors. As discussed in Estimating the Instantaneuus Range 0f 3 Suitablegtandoff distance (say 250 m away) The acoustic

Cttfb',' 'bth ft. .. .'
:ur::n:: i::::1‘:m:n:::::rf:::;: r::1g::ige1al;Ys Eris: 3:36 image is required to reveal the shape and detail (features) of

the ob‘ect, which means the formation of a hi h-resolution
front to traverse two pairs of adjacent sensors to esti.rnate the acoustic image with each Pixel representing 3?‘ area on the
source range from the middle sensor and a source bearing object ~1 Cm lémg by N1 Cm wide The advent of high_fi_e_
with respect to the longitudinal axis of the three-element ar- quency 1_3 Composite Sonar uanéducers with bandwidths
ray. Also, by measuring the differences in both the times of Comparable to their Center frequencies (Lew Q Z 1) means
arrival and the angles of arrival of the ballistic shock wave .

d th 1 bl t bl t_ t_ f th d that the along-range resolution 57 = 1 cm. However, real ap-
an E mull 6 as ma 65 65 um‘ Ion 0 2 range an erture-receivin aira s have coarse cross-ran e resolutions
bearing of the shooter (Lo and Ferguson, 2012). In the ab- f 1 10  h y d d d g h. h
sence of a muzzle blast wave (due to the rifle being fitted with 0 - ml W 1C are range epen am an Prevent lg -

resolution acoustic ima in . The solution is to s thesize a
a muzzle blast suppressor or the excessive transmission loss . I th gthg 1 .yn h
ofa longqmge Shot) the Source (Figure 6 hnmm lefi) can vtrtua aperture so at e cross-range reso ution matc es
still be localized using only time delay measurements of the the along-range resolution (Ferguson and Wyber’ 2009). The
idea of a tomo a hic ima in sonar is to circumnavi ate
shock wave at spatially distributed sensor nodes (Lo and Fer- . gr P g  . . g
2012) F an F t 1 (2007) h dfll “h the rrune at a safe standoff distance while simultaneously
guson‘ ‘ "1 Y‘ erguson 6 a ' S owe a 6 irisoni in the underwater scene which includes the ob'ect
caliber of the bullet and its miss distance can be estimated ofinteféstgmmer than Viewing {he Scene many times fillom
“sing a widebmd Piezoelectric (quartz) dynamic Pressure only one angle (which would improve detection but do noth-
transducer by measuring the peak pressure amplitude and mg for multiaspect target Classification) the plan is to in_
duration ofthe “N” Wave (See Figure 6’ hmmm right)‘ sonify the object only once at a given angle but to repeat the
Hi h F “B sonar process for many different angles. This idea is analogous to
Tm?“ h. I . S spotlight synthetic aperture radar.
grap lc rmzgmg «mar
The deployment of sea mines threatens the freedom of the Tomographic sonar image formation is based on image re-
seas and maritime trade. Sea mines are referred to as asym- construction from projections (Ferguson and Wyber, 2005).
metric threats because the cost of a mine is disproportionately Populating the projection (or observation) space with mea-
small compared with the value of the target. Also, area denial surement data requires irisonifying the object to be imaged
Spring 2019 | Acoustic: Tnduy | 1:

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