Page 18 - Spring 2019
P. 18

Acoustic systems for Defense _ ,
! , 1. \

, , o _;~.>.~3 , .\ \
from all possible directions and recording the impulse re- tn‘ 
sponse of the backscattered signal (or echo) as a function of V "'i _-."i
aspect angle (see Figure 7, left). Applying the inverse Ra- \ i
don transform method or two-dirnensional Fourier transform » t
reconstruction algorithm to the two-dirnensional projection . E-
data enables an irriage to be formed that represents the two- . . .
dimensional spatial distribution of the acoustic reflectivity ’ /-, 
function of the object when projected on the imaging plane \_ 1,

(see Figure 7, bottom right). The monostatic sonar had a
center frequency of 150 kHz and a bandwidth of 100 kHz, g ’i I I
so the range resolution of the sonar transmissions is less than

1 Cm About L000 Views ofthe Object Were recorded 80 that Figure 7. Left: twa-dimensional pmjectinn data ar intensity pint of
the angular increment between projections was 0.35“. Dis- the impulse respnnse af the received snnar signal as ufimctian af time
tinct features in the measured projection data (see Figure 7, (hwilflnffll Imis) I1"d_i”5""1f‘C“"i‘7” “"319 (Vefffiffll flXi5}_- Right’ WP:
left) are the sinusoidal traces associated with point reflectors P:_”‘”g’i“Pi' "f the ”l’-’“t'idi"mZ"" t‘"””g’i“Pi'” S‘"'‘" ’"‘‘'g‘'’ ‘’f the
visible over a wide range of aspect angles (hence, the term i deli" Film liiligiliiii ilii W), ii (2005)

“sinogram"). Because the object is a tnincated cone, which is
radiall s mmetric, the arrival time is constant for the small _ .
specul:r ileflecting facets that form the outermost boundary ;iii;1Ceiliai;g2gi:c‘:s::is ki1i_iif::il::: Fl}i:iCha_:i:sc§uc;:nh:§:iii::si:in::
(iliii ai iliii base) of iliii iiiljeiiii iligiiiie 7’ ilip rigiii’ Sliiiwi a (or forward-lookign milne-hiilhtif sector scan sonar see
photograph of a truncated cone practice mine (1 m diameter . g g . l
, _ , _ , Figure 8, top) was adapted to automate the detection, local-
base, 0.5 m high), which is of fiberglass construction with . . . . . . .
_ , ization, tracking, and classification of a fast inshore craft in
iiiiii iiiiiiig iiigs aiiiii a iiiiiial iiiiil piaie iiioiliiiiiil iiii iiiii iiip a ver shallow water (7 m dee ) hi hl -cluttered environ-
surface. Figure 7, bottom right, shows the projection of the Y . . P i g Y
. . . . . merit. The capability of the system was demonstrated at the
giioiiiiiiiiiial sliapii iii iliii Objiiiii aiiil aiiiiiiiiiii liigliiigiiii iiii HMAS PENGUIN naval base in Middle Harbour Sydney
the image plane. It shows the outer rim, four lifting lugs, i i
and acoustic highlights associated with the end plate. Hence, A 5e‘l“e1"Ce °f 5'3"“ “"3355 {mi 100 C°n5eC““Ve Pings (C°1‘l’€'
tomographic sonar imaging is effective for identifying mines 5P°ndi1"S 1° 3“ °Ve1'“]l °b5e1'V3“°n P91’ 10d 0f 200 5) C3P‘“1'ed
at safe standoff distances. Unlike real aperture sonars, the ‘he nighmme l1mi“5i°n bY 3 Small high'5Peed 5“‘if"‘Ce CW0-
high resolution of the image is independent of the range. Fi§‘“'€ 3» illlfiflm; Sh0W5 the 5°53’ l-‘"335 fmi Ping 51 during
‘ the U-turn of the craft. The wake of the craft is clearly ob-
Naval Base and Port Asset Protection . . . . .
Th _ _d b b_ ct k fth USS COLE_ O t b 2000 served in the sonar u-nage. The clutter in the sonar display is
esuicieommgaaco e in coer b ddb th k “h R d. .td ‘hm
prompted the expansion of a program on the research and de- iiilii i Y e will e 0 i all all is associii e Wi ii
_ _ _ hulls of pleasure craft and the keels of moored yachts. The
velopment of advanced mine-huntmg sonars to include other hi bimensity Vertical Sm at a bearin of 6., is due ‘O ‘he
asyiiiiiliiliiiic illiieaisi liasi liiisiiiiiie iiiiiicli Ciiaii (lllAC)’ iliveiis’ cagritation noise generatediiby the rapidly rotating propeller
and unmanned underwater vehicles. The detection, classifica- . .

_ _ _ _ _ of the craft. In this case, the receiver array and processor of
iiiiii’ iocaiizliiiiiil’ ailil iiiacilliiig ill iiiiise iiiioiliiiiil iisyilliiiieiiiic the sonar act as a assive sonar with cavitation noise as the
threats were demonstrated using both passive and active so- . . P . . .

_ _ _ _ signal. This feature provides an immediate alert to the pres-
mi sigiiiiilipiiiicessiilg ieciiiiiqiliil Tile Passive ilieillolis lliiil ence of the craft in the field of view of the sonar The sonar
already proven themselves inbattlefield acoustic applications. echoes remmed from the wake (bubbles) are pjocessed ‘O
The rotating propeller of a FIAC generates a wake of bub- extract accurate range and bearing information to localize
bles that persists for minutes. When the wake is insonified the source. The number of false alarms is reduced by range
by high-frequency active sonar transmissions, echoes are re- normalization and clutter map processing, which together
ceived from the entire wake, which traces out the trajectory with target position measurement, target detection/track ini-
of the watercraft. Insurgents rely on surprise and fast attack, tiation, and track maintenance are described elsewhere (Lo
so it is necessary to automate the detection, localization, and and Ferguson, 2004). For ping 61, the automated tracking
1s 1 Acuulclcl Tbday 1 Spring 2019

   16   17   18   19   20