 |
| Dolphins swimming in the Atlantic ocean |
By ScienceDaily, July 18, 2012m
Research from the
University of Southampton, which examines how dolphins might process their
sonar signals, could provide a new system for human-made sonar to detect
targets, such as sea mines, in bubbly water.
When hunting prey,
dolphins have been observed to blow 'bubble nets' around schools of fish, which
force the fish to cluster together, making them easier for the dolphins to pick
off. However, such bubble nets would confound the best human-made sonar because
the strong scattering by the bubbles generates 'clutter' in the sonar image,
which cannot be distinguished from the true target.
Taking a dolphin's
sonar and characterising it from an engineering perspective, it is not superior
to the best human-made sonar. Therefore, in blowing bubble nets, dolphins are
either 'blinding' their echolocation sense when hunting or they have a facility
absent in human-made sonar.
The study by
Professor Tim Leighton, from the University's Institute of Sound and Vibration
Research (ISVR), and colleagues examined whether there is a way by which
dolphins might process their sonar signals to distinguish between targets and
clutter in bubbly water.
In the study,
published in Proceedings of the Royal Society A, Professor Leighton along with
Professor Paul White and student Gim Hwa Chua used echolocation pulses of a
type that dolphins emit, but processed them using nonlinear mathematics instead
of the standard way of processing sonar returns. This Biased Pulse Summation
Sonar (BiaPSS) reduced the effect of clutter by relying on the variation in
click amplitude, such as that which occurs when a dolphin emits a sequence of
clicks.
Professor Leighton
says: "We know that dolphins emit sequences of clicks and the amplitude of
each click can vary from one to the next, so that not all the clicks are the
same loudness. We asked, what if this variation in amplitude was not
coincidental, but instead was key to distinguishing fish from bubbles.
"These clicks
were shown to identify targets when processed using nonlinear mathematics,
raising the question of whether dolphins also benefit from such mathematics.
The variation in amplitude of these clicks is the key: it produces changes in
the echoes which can identify the target (fish) in the bubble net, where
human-made sonar does not work.
"Although this
does not conclusively prove that dolphins do use such nonlinear processing, it
demonstrates that humans can detect and classify targets in bubbly water using
dolphin-like sonar pulses, raising intriguing possibilities for dolphin sonar
when they make bubble nets."
BiaPSS was shown to
be effective in distinguishing targets from the clutter generated by bubbles in
the 'field of view' of the sonar. One such target is a sea mine, which is
relatively simple to purchase, and inexpensive (around $1,000 each) compared to
the financial damage (let alone injury and loss of life) that they cause (for
example $96 million repair to USS Samuel B Roberts; $24 million repair to USS
Princeton; $3.6 million to USS Tripoli).
Professor Leighton
adds: "There are still questions to answer. For one thing, dolphins would
have to use a frequency, when they enter bubbly water, which is sufficiently
low that they can hear up to frequencies twice as high in pitch. Until measurements
are taken of wild dolphin sonar as they hunt in bubbly water, these questions
will remain unanswered. What we have shown is that it is not impossible to
distinguish targets in bubbly water using the same sort of pulses that dolphins
use."
The
authors previously proposed a form of sonar signal (TWIPS: Twin Inverted Pulse
Sonar) that could work in bubble clouds, consisting of pairs of pulses that
were identical except that one was inverted with respect to the other, that
could detect targets in bubbly water if the signal processing were to make use
of nonlinear mathematics. However, while these TWIPS pulses were successful,
there was no conclusive evidence that the types of pulses devised for that
study are used by any type of dolphin.
Story Source:
The above story is reprinted from materials provided by University of Southampton, via AlphaGalileo.Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- T. G. Leighton, G. H. Chua And P. R. White. Do dolphins benefit from nonlinear mathematics when processing their sonar returns? Proceedings of the Royal Society A, 2012 DOI: 10.1098/rspa.2012.0247
No comments:
Post a Comment