A. Sarkissian, EXTRACTION OF A TARGET SCATTERING RESPONSE FROM MEASUREMENTS MADE OVER LONG RANGES IN SHALLOW-WATER, The Journal of the Acoustical Society of America, 102(2), 1997, pp. 825-832
The scattering response of a structure may be extracted from acoustic
measurements made in shallow water at relatively long ranges from the
target. The procedure described uses an array of sources to approximat
ely generate a low-order mode and an array of receivers to isolate fro
m the received echo a low-order mode. Since low-order modes behave as
plane waves in the vicinity of the target, the free-field target respo
nse may be extracted from such measurements. In general, such a proced
ure for the generation of a low-order mode requires a large number of
sources. The number is of the order of the number of propagating, none
vanescent modes present in the shallow water environment at the freque
ncies used. If this number is prohibitively large, temporal discrimina
tion may be used in addition to beamforming to reduce the number of so
urces necessary for the isolation of the free-field target response. S
imilarly, the number of receivers required for the isolation of a mode
from the received signal may be reduced by the use of temporal discri
mination in addition to beamforming techniques. This article presents
the detailed procedure used as well as numerical simulations to demons
trate the feasibility of such a process.