By Helen Ward
 |
|
HMAS
Farncomb is fitted with the pickups for the accoustic imaging
trials.
|
|
Photo:
Courtesy DSTO
|
DSTO’s
Maritime Platform Division (MPD) has become an international trail
blazer in the use of acoustic imaging on submarines.
Acoustic imaging enables a defence organization to quantify a
vessel’s acoustic signature and identify from where the noise
is being radiated. It does so by measuring the noise close to
the vessel and then projecting into the distance.
MPD’s developments enable accurate measurements to be taken
without the need for a vessel to go to range, resulting in significant
time and cost savings for Navy.
The software and techniques developed by MPD have also sparked
a keen interest by the Naval Research Laboratory (NRL) in the
USA, which is recognised as the pioneer of acoustic imaging.
NRL developed the original acoustic holography theory and processing,
but had concerns about transforming it from the lab to real life.
In particular, there were questions about obtaining the precision
it considered necessary.
MPD looked at both the question of precision and the robustness
of the methodology and proved that it was possible to make meaningful
measurements on a submarine in the real world.
The acoustic imaging program began in 1997 using software that
was developed for the automotive industry.
MPD adapted the technique for use on submarines and first demonstrated
its effectiveness in 1998 when tests were carried out on the submarine
HMAS Farncomb.
Farncomb had been experiencing machinery noise for some time and
though the source of the noise was known, the transmission path
proved elusive.
Using
its acoustic imaging technology, MPD was able to monitor the noise
behaviour, identify the transmission path and then devise a suitable
solution.
In 2000 NRL paid MPD to provide a demonstration of the “real
world” system at the USN SEAFAC range in Alaska.
MPD has also used the system to investigate the noise generated
by the fin top exhaust on submarines. Using a special test rig
the system was used to measure and provide a picture of the noise
from the exhaust outlet all the way to the surface. This enabled
the loudest parts of the exhaust to be identified and provided
the basis for work in reducing the exhaust noise.
These tests were undertaken in conjunction with Kockums in Sweden,
who were keen to see the system in operation and visualise the
noise in the exhaust cloud.
Despite MPD’s developments there is still plenty of work
to be done to refine the project. One current drawback is that
the technology only identifies and transmits machinery noise,
not propulsion associated noise.
Nevertheless, MPD is working hard to overcome the problem and
is confident it is on the right track to achieve its full operational
effectiveness.
