Underwater Sonar: Side-Scan Imaging Sonar & Forward Looking Sonar for Obstacle Avoidance & Navigation

Simultaneous In-band Active & Passive Sonar for Threat Detection

Feature Article by Wavefront Systems
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Wavefront Systems has released the following article highlighting the advantages of its Sentinel Intruder Detection Sonar for threat detection aboard crewed and uncrewed vessels. The latest generation of Sentinel takes advantage of cutting-edge Simultaneous In-band Active and Passive Sonar technology.

There is no doubt that as technology advances, whatever sector it may be in, not a week goes by without new and improved products launching onto the market. While this is very exciting, potential threats to our security are also evolving at the same pace. As a company, we at Wavefront are mindful of how quickly this is happening and therefore we must ensure our sonar products stay at the forefront of innovation.

Whilst developing this latest generation of our Sentinel Intruder Detection Sonar, our analysis of the rapidly evolving drone threat led us to the conclusion that it had to be more than just an incremental upgrade of the previous versions of Sentinel, the world’s most deployed Intruder Detection Sonar. We should try, as part of this development, to take advantage of potential gains provided by passive processing but crucially without compromising the existing active performance. Subsequently we developed SInAPS.

So, what is SInAPS and why is it so powerful?

Simultaneous In-band Active and Passive Sonar, SInAPS, combines the existing active system with a new passive tracking capability which tracks the target by listening to the noise it is emitting. This is highly innovative and uses the same array for both active and passive processing simultaneously.

SInAPS has the unique advantages of:

  • Retaining the processing gain of the Sentinel array, with over 30 dB higher than a single hydrophone sensor, and dramatically enhancing passive signal to noise ratio (SNR).
  • Retaining the high bearing resolution associated with operating at higher frequencies with no need for a distributed sensor network.
  • Guaranteeing spatially co-registered tracking between active and passive sub-systems from a point sensor.
  • Avoiding the need for the system to be switched ‘optimally’ between active and passive operating modes.
  • Finally, and crucially, it retains the performance of the system’s active mode without being compromised.


The above screenshot shows a critical alert, in red, tracking a diver from 950 metres. Aligned to the diver’s current position is a simultaneous passive track showing bearing over time, where the last 5 minutes of passive tracking lines up with the divers’ movements. The combination of positive intent, the diver is headed straight for the protected asset, and mechanical noise detected from a single sonar head means this is the highest priority of threat.


Sentinel IDS: The sonar solution for mobile and fixed use

The situations where the need for IDS will vary, depending on the security risk at that time. Sentinel delivers a flexible solution, covering you when you need either a fixed or mobile sonar. For example, Sentinel’s ability to be used in a mobile situation comes into its own when vessels at anchor need rapid deployment for short periods or locations where seabed deployment is just not possible.

There are of course many factors that must be considered when developing sonar for non-fixed deployment.

The basic theory behind any ‘tracking’ sonar, like Sentinel, is that you can determine the range and bearing to the target being tracked, all relative to the sonar head. Over time you can then monitor the behaviour (speed, direction, etc) of the target to determine if it is a threat or just marine life. This is fine for a static sonar as you are tracking everything relative to the sonar and you know the position of the sonar head. However, when deploying from a moving platform, we need to be able to calculate out the movement of the head, otherwise static objects would look like they are moving. We do this by inputting platform heading, pitch, roll and position. The system uses this information, in real time, to geolocate the returns from the sonar and determine the relative position and movement of the target.

Mobile sonar installation options

One of the biggest advantages of mobile Sentinel is that its capabilities have opened up a number of different deployment options:

  • Vessels at anchor. Wavefront offer complete deployment solutions, including Sentinel systems that can be deployed on hydraulic rams below the vessel or ‘over-the-side’ swing-arms.
  • Buoy mounted Sentinel. Fully autonomous, buoy mounted solutions for deployment in remote locations or where seabed stands are not appropriate.
  • ‘Sprint and Drift.’ Enabling manned or unmanned vessel to move quickly into position and deploy Sentinel whilst drifting in the current.

In Conclusion

The key takeaway from this article has to be that the development of this unique and highly advanced SInAPS sonar technology allows IDS to identify and track threats faster and more effectively than ever before.

To learn more, contact Wavefront Systems: Visit Website Send Message View Supplier Profile
Posted by Mike Ball Mike Ball is our resident technical editor here at Unmanned Systems Technology. Combining his passion for teaching, advanced engineering and all things unmanned, Mike keeps a watchful eye over everything related to the unmanned technical sector. With over 10 years’ experience in the unmanned field and a degree in engineering, Mike’s been heading up our technical team here for the last 8 years. Connect & Contact