Challenges & Solutions
The DSTO research and development team had to face innumerable challenges. A few are outlined here.
What array to use?
This decision was complex and involved a compromise between performance, mechanical design and cost. The more hydrophones the better the performance, but the greater the complexity, the more difficult the reliability and the higher the cost. After much study it was decided to use an array of 25 hydrophones, with 5 mounted on each of 5 radial arms. The overall diameter of the array was 5m. Read more.
The customers (the RAAF, RAN and RAF) required that everything had to fit into a small standard sonobuoy canister.
How on earth could such a large array with hundreds of components, be crammed into such a small volume? Knowledgeable sonobuoy designers overseas thought it could never be done, let alone be manufactured at an acceptable cost and operate with the required high level of reliability.
Various mechanical designs were considered. Eventually it was decided to use telescopic arms.
When the sonobuoy was conceived, integrated circuits were only in development in laboratories but the inventors anticipated their arrival in time to allow electronics to be made small enough.
Industry modifications to the DSTO preliminary design helped reduce cost and improve reliability. Read more
All the sounds radioed from the sonobuoy have to be processed in the aircraft, to distinguish signals from noise, to decide where the sounds were coming from, and to decide whether each sound was from a ship, a submarine or a fish. How can this complex signal processing be implemented in equipment carried in Air Force and Navy anti-submarine aircraft and helicopters?
In the then current state of technology the experimental equipment was heavy and occupied a large volume. The DSTO team carried out wide-ranging feasibility studies to establish that a versatile computer-based processor, of a size and weight that would fit into an aircraft, would be able to perform these tasks. These studies included development of experimental equipment and extensive tests and trials of processing techniques and operator requirements.
Under the joint project, the UK developed a powerful computer (by the standards of the time!) to carry out all this processing. Read more about Signal Processing.
There were numerous other design details to be resolved:
- A compass is needed to show the orientation of the array; how accurate does it have to be? Read more
- Performance can be degraded by the least motion of the hydrophones. How can the array be isolated from the motion of the buoy on the sea surface? Read more
- All the signals have to be sent to the aircraft inside the existing frequency channels allocated. How can this be done? Read more
Design specifications were very severe: sonobuoys have to undergo extremely cold temperatures, survive the impact into the water, even in heavy seas, and operate reliably for many hours. How can there be confidence that the sonobuoy will work reliably under all operational conditions?
An elaborate test facility was used to demonstrate the feasibility of the design. It was constructed in a deep, fresh water hole in the south-east of South Australia, chosen because of the remarkable clarity of the water. Engineers in industry used advanced design tools to assure reliability. Production batches are tested at sea. Read more.
There are many noises in the sea that can mask the faint sounds from submarines. "Ambient noise" in the sea is generated from breaking waves and rain; marine creatures make a wide variety of sounds. Ships, even at a great distance, add to the background noise. Then there is unwanted noise generated by the sonobuoy system itself.
How to suppress all this noise?
Listen to sounds in the sea from fish, ships and submarines
Signal processing plays a large role in reducing noise.
Steps can be taken against each of the sources of self-noise in the system. Read more about self-noise.