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Nexus 2 is the second release of our popular digital USBL system. Originally released in 2016, it enabled a higher level of accuracy and repeatability, incorporating our Sigma 2 spread spectrum channels which added additional functionality as well as a higher level of accuracy and repeatability. 

Customers enjoy working with our Nexus 2 system for a variety of reasons, but primarily its ease of use and the results achieved when using the system.

Do you need to accurately position your ROV/AUV subsea?

How about your towed magnetometer for UXO surveys?

applied acoustics have been manufacturing survey-grade USBL systems since 2010 and the Nexus 2 system is a high-grade solution for positioning and navigation subsea. We’ve achieved great success within a number of key sectors, from Oil and Gas to Renewables, Defence, Ocean Science, Aquaculture, Port and Harbour Surveys, and UXO Surveys and Clearance.

Helping subsea service specialists deliver a better experience for their clients

Ocean Scan knew aae were experts in technology associated with underwater positioning systems in conjunction with ROV equipment and approached us for technological help. Positioning accuracy is essential for the company’s work in identifying shipwrecks, debris, pipelines and underwater hazards. 

aae assisted with the successful integration of several USBL systems into Ocean Scan’s Falcon DR-1000 ROVs, which are now performing high-depth marine infrastructure inspection work for a range of industries. These USBL systems have significantly improved Ocean Scan’s subsea operations, making it possible for them to deliver a better experience for their clients and achieve a higher level of satisfaction with all their undersea inspection work.

Ocean Scan

The evolution of the Nexus 2 USBL

applied acoustics have been manufacturing USBL systems for over 25 years, starting with the original analogue Easytrak USBL system, and now using spread spectrum digital signal architecture for the last 11+ years. 

The Nexus USBL system was released in 2010 to allow higher levels of accuracy, with Nexus 2 following six years later, taking advantage of further technical advances. Our Sigma 2 spread spectrum digital acoustics lifted Nexus 2 to survey-grade navigation and positioning.

Nexus 2 highlights

  • An established, highly advanced USBL system, with over 150 Nexus systems sold worldwide to a variety of customers.
  • Standard bi-directional Sigma 2 spread spectrum offering quality acoustics with added functionality, superb accuracy and repeatability in shallow or deep waters.
  • Fast Acoustic Data Uplink- an 800bps (including forward error correction) protocol allowing quick, secure and reliable data transfer between subsea instruments and surface command.
  • ‘Multi-Fire’ Common Interrogate Function; the capacity to interrogate multiple subsea transponders with a single ping, giving faster update rates than conventional sequential firing, utilising our proven and proprietary Sigma 2 acoustic protocols.
  • EasyCal 2 embedded calibration software provided as standard, saving valuable set-up time, ensuring operations can begin quickly and efficiently.
  • Windows based software for ease of use.
  • Industry standard VRU, DGPS, Heading, Depth Input and DP Telegrams, providing our customers with confidence that Nexus 2 has everything you need.
  • Transceiver options available, capable of tracking fast moving targets at long slant ranges. Reliable, repeatable and accurate results have been achieved with towed targets moving at 10 knots. Particularly effective for UXO surveys utilising several magnetometers or sidescan sonars, diving operations, and for use at offshore worksites where several vehicles may be in use concurrently. The long range capability and exceptional accuracy specifications make Nexus 2 particularly effective for long layback towed application. 

Customer satisfaction

“The experience of working with aae has been very good. USBL equipment has a technological development that allows for easy handling and a fast-learning curve for its operation. Technical support has always been there when solving a problem. In general, our experience with aae has been very satisfying.”

Alex Lobos Astudillo, Head of Hydrography and Oceanography at Ocean Scan

Get the right USBL for your project

If you feel that the Nexus 2 system is maybe more than you need to achieve required results or you haven’t quite got the budget, just drop us a call or an email. We will be happy to talk through your specific requirements and suggest the right system from our USBL product family to suit your project down to the ground. Or the seafloor! 

Do you need highly advanced positioning and tracking with all the bells and whistles that is quick and easy to deploy, straightforward to operate and works in any subsea industry sector? Don’t hesitate to contact us or browse the Nexus 2 specs here. A quick conversation with our sales team will confirm if the Nexus 2 is the right USBL for you.

Divers are used throughout different industries for a variety of tasks; from inspection, maintenance and repair of subsea structures in the offshore energy sector, research and environmental management, to military applications. Knowing the location of people in the water is critical to the safe operation of work being undertaken.

A USBL system designed for shallow-water tracking can accurately determine the position and depth of subsea divers in all environments for reliable and safe systems of work. A USBL system also allows for the marking of targets and waypoints to assist a diver’s navigation in poor visibility.

However, effective diver tracking relies on understanding the intricacies and key features of a USBL system, so you can put it to optimum use. With that in mind, here are some of our top tips.  

1. Get your acoustic signal right 

Receiving a good acoustic signal is the most important element to achieving a reliable position, and the setup of the vessel transducer is key to this.

The transducer of the USBL system should be at least one metre below the hull of the vessel that it is being installed on to obtain an unobstructed 360° view below the surface of the water. This reduces the impact of acoustic reflections, which can result in inaccuracies of position. Any installation should be as clear as possible from potential sources of acoustic noise such as thrusters and propeller wash. 

The tracking transducer should be located as close as possible to the vessel’s centre of gravity, to minimise movement during operations. Vessel transducers can be pole mounted (recommended) or free hung if cabling is suitable.

2. Set your transducer depth 

Once installed, the USBL system should have the transducer depth entered, if required, so that accurate Z position (depth of target) can be calculated. Some systems like the Nexus 2 have built-in depth sensors so this is all taken care of. If using a reference position from a GPS or CRP, for example, then the offsets to this point must also be correctly entered. Failure to do this will result in positional errors. However, it is important not to duplicate these offsets in other third-party software.

3. Set the speed of sound through the water (VOS)

A fundamental for all USBL subsea positioning systems is the speed of sound of the water. Depending on a number of variables such as salinity, depth and temperature, the velocity will vary from 1440 to 1520 metres per second. If a velocity profile or measurement is unavailable, applied acoustics systems have calculation tools available.

4. Prepare for shallow water  

For the majority of dive operations the diver will be in shallow water, often around structures or sources of reflection. Turning the power down on the transmission and reducing the gain in the tracking system can often reduce the background noise and provide a more stable position, reducing multipath signals.

Some systems will have automatic gain controls and others will be manual. Make sure to consult the operation manual so you’re familiar with these.

5. Select the right beacon and channel

Choosing the correct beacon and channel for operation will allow the operator to track the diver effectively while minimising carry weight for the diver and removing excess noise that can saturate the receivers in the tracking head and cause errors.

For diver tracking, a compact omnidirectional beacon complete with depth sensor is recommended to ensure beam pattern alignment between the beacon and tracking transducer, as well as an accurate depth (Z) measurement. This aids the positional calculation performed by the USBL system. applied acoustics now offers the 1329D with a built-in depth sensor as standard, which improves the accuracy of position and reliability of results.

Each beacon is set to a unique channel to prevent crosstalk and interference with any nearby operations. It is recommended to use a digital encoded channel scheme, for example, applied acoustics Sigma 2, which provides stable positioning and noise immunity. If using legacy CW tone channels, ensure channel separation greater than 500Hz in the uplink and downlink frequency.   

6. Beacon location

Remember the acoustic path between the beacon and the tracking transducer is line of sight. Therefore the mounting position on the diver or subsea system has a significant role in system performance.

Our USBL systems at a glance


The Alpha USBL system is designed for quick setup and versatile shallow water use, so is ideal for tracking divers who generally operate within 500m of the vessel. It is a mobile unit designed for quick deployment on small vessels and provides basic tracking and positioning, making it ideal for most small surveying and inspection jobs. It can track up to four targets and doesn’t need a fixed mounting due to internal AHRS sensors.

Our Nexus systems provide a suite of tools for more accurate positioning and surveys. They allow for sigma spread spectrum technology, which offers a secure acoustic link to reduce the system’s susceptibility to interference. This is important when tracking in shallow-water environments where divers are typically utilised.

For optimum shallow water diver tracking, our INS + USBL system Pyxis is the most accurate in the Easytrak USBL range. Combining our bi-directional Sigma 2 spread spectrum acoustic protocol with a factory-fitted inertial navigation system (INS), the system is highly accurate, stable and calibration free, enabling rapid deployment and tracking. 

For more information on any of our systems, acoustic beacons or to discuss your application, please feel free to contact the team