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the multipath is much simplified and primarily consisted of Hefereneee
a direct and surface-bounce signal with little refraction from  
the sound column. Under these circumstances, no knowl- B3§3"°”* A‘ B'*K“h°’“‘3"‘w' ft’ 3nd Mfld‘3l“_"‘kV’ RA‘ 0991)‘ A“°""f
d f in _ r _ _ d d _ I _ View of matched field methods in ocean acoustics. lEEE]imrmzl afDce1mic
e ge o e ocea.n environmen is require an a simp e irn- Enginming is“), Mn_424_
age theory calculation can be used. as seen in Figure 6. McCargar, 11., and Zurk, 1. M. (2013). Depth-based signal separation with
' 'tlicl .The lthA t'lS'
From a mathematical standpoint, the coherent addition of  Immm 0', 8 mm Km may
the two multipath signals at the receiver as the source tran- Ogden, G. L, Zurk,L M., Jones, M. F... and Petusnm M. F. (2011). Extrac-
sits in range can be represented as a tirne_varying signa_i_ -i-he tion of small boat harmonic signatures from prmive sonar. The Iourmzl uf
. . the Acoustical Society |7fAmeric11 129(6), 3768-3776.
frequency of the interference between the direct and surface our H” Am W W) Zmk L M“ and Lammm) M or (201 st Amommd sx_
bounce can be directly related to the source depth, and a tame“ and dassificafion 0fi_in.ie_fmquen,_-y canton“ in h,,,,,pbaek,,Ma1_
modified Fourier transform can be applied to the output of imions. Thelounml q/theAmusn‘ml Society ufAmm'm 133(1), 301-310.
a VLA over time (this is defined as a vertical time record U"{‘d: R‘ I‘ 0983)‘ P”"‘’Ple‘ 9’ U"‘l"“”“e’ s“”"'l' M‘G“""'H""‘ New
. . or
WTRD‘ A5 ““ e’‘3“‘P1e' 3 5“““1““-‘°“ °m‘e VTR f°’ 3 5°““e Van Trees, 1-1. 1., and Bell. K L (1968). Detection, Estimation and Modula-
radiating energy at 150 Hz in a 5,000-meter channel is shown tiim Theory. Wiley, New York.
in Figure 7, lefi, for a surface (top) and submerged (bottom) Zuxk 1-. M.. Let, N.. and Ward, 1- (2003)- SWYCE 51050" flhhiahhfl 50’
source. Note that the incident angle measured on the VLA  ;‘E‘C:7°;l9fi;J7’:1"'°€°sSi"e‘ The l'"‘"'”l “fa” Am"mmls°C'"7 "f
changes over time as the source transits in the vicinity of the ) '
array. Figure 7, right, shows the transform output as a func-
tion of source depth, and the peaks correctly appear at the Eioskabch
source depth (McCargar a.nd Zurk, 2013), with the peaks for  
the 5“Tf3‘3e 5°““3e 3PPed'h‘3 at 1 '3‘ h‘ deP‘h (WP: “'43) and Lisa Zurk is the executive director of the
at 50 m for the submerged source (bottom, red). Applied physics Laboratory at the Uni_
versity of Washington (UW), Seattle,
:°"‘=h"3i°"3 and a professor in the Electrical Engi-
iAcoustic sensing in underwater channels is quite challeng- I neering Departrnent at Uw previpnsiyt
ing due to the complicated structure of many sources (both . she served as a prpgrarn rnanager at the
passive radiation and active reflected) and the propagation Defense Advanced projects Research
physics. Several techniques have been devised to exploit this Agency_ as a professor of electrical and
temlmffl-la 51795‘-T31» and SP3‘-la-1 Smlchlffia and 3PPh°dfi°h df computer engineering at Portland State University, OR, and
these dlgdrhhhhs ed“ lead to e“h3-heed deieel-ldhv C_l3-‘sided’ as an associate group leader at the MIT Lincoln Laboratory.
mm» 3‘‘d ldcdhzdhdh df “hderw3‘e’ 5°‘“Ce5- 1-“ the “melee She is the author of over 50 technical papers and has received
3 Short ih"°d“Ch°h ‘O PhY5iC5'bd5ed Sigh“! Processing h35 multiple recognitions, including the Presidential Early Ca-
heeh Provided with ex3h‘P1e5 fmm ‘he 1'e5e3“h hierdthhe reer Award for Scientists and Engineers, the National Sci-
applied to biological and man-made sources In both shallow ence Foundation CAREER Amrd, a Fulbright scholarship,
3hd deePW3‘e‘ ehVh'°hmeh‘5- and the Oflice of Naval Research Early Faculty Award.
.......-..... a_.......... 1 a . - . v
- -
Acoustical Society of America
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