U.S. military planners have become concerned that rogue states or terrorist
groups may acquire Russian Kilo-class, diesel-electric submarines and equip
them with “air independent propulsion.”
Diesel-electric submarines using air independent propulsion can remain submerged
for extended periods of up to two or three weeks, and unlike nuclear submarines,
diesel-electric submarines can “bottom out” or rest on the ocean
floor.
Since shallow coastal regions are complex and noisy, the detection of such
diesel-electric submarines is not possible using traditional acoustic methods.
With air-independent propulsion, the fuel source and reused exhaust gases are
combined in a closed loop to generate a submarine’s power. Current power
plants include closed-cycle diesel engines and, more recently, fuel cells.
This form of propulsion, while not used by the United States, Britain or Russia,
is used by smaller navies. It is considered ideal for small vessels, is cheaper
to operate and makes the submarine more difficult to detect.
Diesel-electric submarines can provide a formidable challenge to current surveillance
systems. The high ambient noise levels from local shipping traffic and marine
life make passive sonar detection almost impossible in littoral waters.
The challenge of detecting diesel-electric submarines is best illustrated by
an example from the Falklands War. During that conflict, the British Royal Navy
could not defeat a single Argentinean diesel-electric submarine, although the
British were highly experienced and released more than 150 weapons with no hits
scored.
Low-frequency active sonar technology, such as the surveillance towed-array
sensor system, may be an effective alternative to passive detection, but is
politically disadvantaged because it has been reported to harm marine mammals.
Detecting submarines in littoral waters is comparable to locating landmines.
It requires fusing data from a variety of sensors to pull the hidden signal
out of the noise.
One of the technologies now being used by the German and Swedish navies to
counter the threat of quiet submarines is a software architecture called the
scalable generic signal processor, or scalable GSP.
The German Navy selected the scalable GSP technology for its new underwater
acoustic analysis system, to be located at the Federal German Navy Hydroacoustic
Analysis Centre.
The analysis system was designed to analyze the sonar records of the new U212A
submarines, the U206A submarine, maritime patrol aircraft and fleet vessels.
The scalable GSP technology is built on an open-architecture cluster of parallel,
off-the-shelf, general-purpose processors using Linux, an open-source operating
system. The term “scalable” describes the ability of the control
software to recognize and utilize the available processors, whether one, 10
or hundreds.
The data-processing rate may be increased with the addition of processors,
without a need to re-write or recompile the software. Conversely, single processor
failures simply reduce processing speed. Users can add their own software modules
to meet specific needs, such as the introduction of classified algorithms.
The scalable GSP employs a “Lego” style technique that allows users
to graphically modify existing applications or to construct new applications
with building blocks of processing functions.
The technology has been adopted internationally for sonar applications, and
has been used in synthetic aperture radar processing.
Brian Markle is the chief technology officer of Array Systems Computing Inc.,
a supplier of scalable generic signal processor technology, based in Toronto,
Canada.