Inventor's Month: Northern Diver's underwater navigation, sonar and combat swimming systems

Posted 13/08/2018

For Inventor's Month, we're documenting some of the interesting research and development that forms part of daily life at Northern Diver HQ and the innovative products we work to create as a result.

Whether it's swift water rescue, offshore windfarms or special military operations, the numerous sub divisions of Northern Diver mean we enjoy working on many diverse projects. Recently we've developed systems for underwater navigation and sonar, explosive ordnance disposal (EOD), combat swimming and surveying. These systems are designed mainly for military diving use, though most are also suitable for search and rescue, police divers, archaeological survey and the offshore industries.

The Northern Diver NIMROD underwater navigation and sonar group of products

Our family of NIMROD devices brought together a development team with over 40 years' experience in ROV design, military and commercial diving.

The project started with the original NIMROD handheld console. Machined from a single plate of aluminium, the item was developed so that the user can locate objects of interest by way of single beam sonar (for example when conducting explosive ordnance disposal operations) and navigate between waypoints with no need for surfacing.

The system is designed to work with a PC via a Bluetooth interface, which allows the mission plan to be devised and uploaded to the NIMROD, with the diver then able to interact with the mission plan on the NIMROD console and add other points of interest if necessary.

The ubiquitous Global Positioning System (GPS), used in countless applications for geolocation services, doesn't function underwater, so for integration of GPS with the NIMROD - one of two of the device's user positioning options - the system can be used with a supplied GPS float, located in situ at the water's surface and towed by the operative.

This GPS facility enables the NIMROD to sync user location with the unit's heading, depth and attitude sensors to present a dynamic navigation feed to the user, with an aircraft-style artificial horizon for attitude control and imaging displayed from the sonar.

Depending on the user position in the water, the unit's two handles and sonar bracket can be adjusted to suitable positions in order to maximise effectiveness.

Data recorded from the mission can be extracted via Bluetooth and evaluated.

Doppler Velocity Log technology

The NIMROD's alternative to GPS, which negates the need for the float, is known as a Doppler Velocity Log (DVL).

Available as a modular extension, the DVL operates within the same principles as the Doppler Effect.

If you've ever noticed the change in pitch of, for example, an emergency vehicle siren as it approaches and then passes you, this is one example of the Doppler Effect at work.

What is happening comes down to waves - in this case, sound waves. The sound waves are affected by the direction of travel and have a shorter wavelength and therefore higher frequency (pitch) in front of the vehicle, and vice-versa behind the vehicle - resulting in the familiar sound of a higher pitch followed by a lower pitch as the vehicle passes you.

In relation to the NIMROD's DVL system, the module, otherwise known as an acoustic sensor, operates by emitting a sustained pulse through acoustic beams in four different directions towards the sea bed. This creates an axis of reference used to calculate velocity (speed) through measuring frequency shift, and ultimately, tracks the diver's direction of travel. This method is favoured when a stealth approach is required.

While it's a very effective form of propulsion, human finning power can only go so far, so we've recently adapted this system for use with a the Apollo AVX underwater scooter.

Multibeam sonar imaging

Multibeam sonars - you guessed it - emit multiple beams, rather than the aforementioned single beam sonar. Single beams easily meet the demands of many applications, but when a more detailed survey is required, multibeams really come to the fore and their ability to pick up smaller details is an essential tool.

The images presented by multibeam sonars can be likened to a video feed, and they give a wider field of vision than single beam sonars.

The detail shown gives a crisper image of the area of interest, thanks to the exponentially increased amount of beams. The Gemini 720im, one of two multibeam sonars we currently offer, is the world's smallest multibeam imaging sonar and employs 128 beams. The Gemini 720ik model has 512 beams, giving real-time imagery comparable to video. Both units are available with the NIMROD Elite system, which can be supplied with either a GPS float or DVL. For this NIMROD version, we worked to develop an updated housing for the system.

Combat swimming

Combat swimming can see personnel swimming for miles. The US Navy SEALS even developed a style of swimming known as combat swim stroke (CSS) to keep the swimmer relaxed and maximise their efficiency. The stroke is a fusion of breaststroke, front crawl and sidestroke - see it in action here.

Swimming in combat presents other unique challenges. We developed the Digital Depth Gauge as a useful wrist-worn device for combat swimmers that feeds information about the dive to them through the OLED display, including current depth, maximum depth, dive duration exceeding max depth, and dive time.

With a maximum working depth of 100 metres, the device was designed to have a lengthy battery life and highly accurate depth sensor.

Like the NIMROD, information from the dive can be extracted to a PC. With the Digital Depth Gauge, this is completed via a docking station, designed by Northern Diver and utilising optical technology to download the data through the face of the gauge.


To be able to work with such a diverse and interesting range of clients is what we thrive on at Northern Diver. We hope you found it interesting to read about this arm of our business, which never stands still!

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