Shadow Enhancement in Synthetic Aperture Sonar Using Fixed Focusing
article
Abstract—A shadow cast by an object on the seafloor is important
information for target recognition in synthetic aperture sonar
(SAS) images. Synthetic aperture imaging causes a fundamental
limitation to shadow clarity because the illuminator is moved
during the data collection. This leads to a blend of echo and
shadow, or geometrical fill-in in the shadow region. The fill-in is
most dominant for widebeam synthetic aperture imaging systems.
By treating the shadow as a moving target and compensating
for the motion during the synthetic aperture imagery, we avoid
the geometrical shadow fill-in. We show this to be equivalent to
fixing the focus at the range of the shadow caster. This novel
technique, referred to as fixed focus shadow enhancement (FFSE)
can be used directly as an imaging method on hydrophone data
or as a postprocessing technique on the complex SAS image. We
demonstrate the FFSE technique on simulated data and on real
data from a rail-based SAS, and on two different SAS systems
operated on a HUGIN autonomous underwater vehicle.
information for target recognition in synthetic aperture sonar
(SAS) images. Synthetic aperture imaging causes a fundamental
limitation to shadow clarity because the illuminator is moved
during the data collection. This leads to a blend of echo and
shadow, or geometrical fill-in in the shadow region. The fill-in is
most dominant for widebeam synthetic aperture imaging systems.
By treating the shadow as a moving target and compensating
for the motion during the synthetic aperture imagery, we avoid
the geometrical shadow fill-in. We show this to be equivalent to
fixing the focus at the range of the shadow caster. This novel
technique, referred to as fixed focus shadow enhancement (FFSE)
can be used directly as an imaging method on hydrophone data
or as a postprocessing technique on the complex SAS image. We
demonstrate the FFSE technique on simulated data and on real
data from a rail-based SAS, and on two different SAS systems
operated on a HUGIN autonomous underwater vehicle.
TNO Identifier
347371
Source
IEEE Journal of Oceanic Engineering, 34(July), pp. 269-283.
Pages
269-283
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