Sonardyne’s 6G product range is designed for use in a wide variety of applications. To get the best performance out of the 6G family of hardware, the user can choose acoustic addresses linked to their acoustic operating frequency. These acoustic addresses are configured directly using Sonardyne’s 6G terminal software or even acoustically whilst in the water!

For USBL operations the user will usually be using either a Wideband 2 or a wideband 2+ acoustic addresses, these both operate between 19 and 32kHz. The difference between the two modes is that Wideband 2 addresses (which are appropriate for 90% of working conditions) utilise an 8ms navigation pulse compared to Wideband 2+ which utilises a 16ms navigation pulse. Whilst Wideband 2 is appropriate for the majority of applications, when operating in acoustically noisy conditions the longer pulse duration of the Wideband 2+ signal combined with the advanced onboard digital processing results in a more robust tracking solution. Users should note that if using Wideband 2+ it takes twice the energy to transmit these signals. Battery levels and consumption should be considered carefully.

Acoustic Address Families

Beacon addresses are broken down into channels with 14 addresses per channel. Each acoustic channel operates at a fixed frequency.

• The Wideband 2 family of addresses starts at 17xx (with individual acoustic addresses of 1701-1714) and finishes at 31xx (with individual acoustic addresses of 3101-3114).
• The Wideband 2+ family of addresses starts at 50xx (with individual acoustic addresses of 5001-5014) and finishes at 63xx (with individual acoustic addresses of 6301-6314).

When configuring a unit for operation at specific frequencies, the user must be aware of the following terms, the two different interrogation/reply methods and the fact that the user will need to set both of these if trying to avoid noise sources.

• IIS (Individual Interrogation Scheme) – When only a single transponder is being tracked or when multiple transponders are being tracked with different update rates IIS may be used. Only a beacon with the correct acoustic address will reply to this interrogation.
• CRS (Common Reply Scheme) – CRS is utilised for the reply pulse of an IIS interrogation.
• CIS (Common Interrogation Scheme) – When interrogating multiple beacons, using a common interrogation scheme is advised, this is common practice with USBL and is much more efficient than individual interrogations as all configured responder will reply to the same initial interrogation.
• IRS (Individual Reply Scheme) – IRS is utilised for the reply pulse of a CIS interrogation.

Choosing an Address

When choosing an appropriate acoustic address, the following factors should be considered:

• Is there a need for longer range navigation? – The lower the frequency of the acoustic pulse the lower the attenuation of the water that the signal will travel through.
• Is there a noise spike within the frequency range? – Using the FFT (Fast Fourier Transform) functionality built into 6G hardware it is possible to identify noise spikes to be able to adjust operating frequencies to improve performance.
• Is the system operating in a noisy and/or reverberant environment? – As mentioned, Wideband 2+ has a double-length pulse which allows for better performance in more challenging environments.

Using Depth Aiding

When using Depth aiding two consecutive family addresses are utilised. The first reply will be on the transponders IRS address to ascertain the range of the unit, the unit then delays a second range reply that is the equivalent of the transponders depth before the consecutive address transmits. When planning to use depth aiding it is important to ensure that transponders are not configured on consecutive addresses as these will clash with the depth aiding reply.

Avoiding Noise Spikes

Within Ranger 2 is built in an FFT plotter. This should be the first tool of use when the 6G transceiver is deployed for the first time to ensure that there are no noise spikes within the operating frequency.

The information used in the following chart shows a transceiver with a very low noise floor of around 70dB for the first two-thirds of the usable frequency spectrum. For optimum performance, acoustic interrogation and reply frequencies at 24kHz and below should be used.

In some installations, there may be a raised noise floor and noise spikes to contend with, in the following example the acoustic noise floor is in the region of 10-20dB higher than our previous example, in addition to this there is a noise spike centred around the 38kHz mark spreading down to the 25kHz region.

In this example, lower frequency interrogation and reply addresses should be utilised, if operating at longer ranges it may be necessary to utilise WideBand 2+ for the associated processing gains in defeating the high noise floor.

In the following noise plot, there is a significant noise source in the lower end of the frequency spectrum. The use of a higher operating frequency would be a big advantage in this situation.

The information provided above is a very brief introduction into the challenges and mitigation of noise sources. More information and in-depth training are available by contacting Sonardyne.

CASIUS result can indicate more about the system than just the transceiver misalignment values. Quick checks can reveal information on Ranger 2 USBL or Marksman LUSBL system behavior.

CASIUS (Calibration of Attitude Sensors in USBL Systems) primarily computes the misalignment between the transceiver and the ships motion reference units. It also provides an indication of system performance, errors in dimension control, deployment pole integrity, GNSS quality, MRU errors and noise interference sectors. From these result corrections can be made to improve the systems performance an accuracy.

The scatter distribution is summarised as a statistic compared to water depth so 100m depths should result in a scatter of approximately 10cm 1DRMS. If the calibration lines exceed ½ the water depth horizontal offset, refraction errors can bias the data.

Calibrating in shallow water <50m tends not to produce consistent results because the GNSS and MRU error is invariably larger than the acoustic jitter and misalignments are lost in the noise.

• Check the computed offsets don’t differ significantly from measured values.
• Check computed sound speed agrees with expected. This is often scaled in error to attempt to resolve data outside ½ waterdepth.
• Check processing results agree with the tidal model result confirming reliable GNSS height.
• Check the error result is within expected error budget.
• Check all clusters are similar levels of noise as some observations, using astern propulsion, can suffer aeration.
• Check which data collection points have outliers and does this correlate to certain vessel headings?
• Is the data more spread in a certain axis or geometry as this indicates whether Pitch and Roll out perform Heading error.
• Poor repeatability can indicate pole movement.

Larger spread on lines exceeding ½ water depth.

Carrying out a USBL calibration is an essential step to get the most out of the system, over the years we have seen a number of simple steps which when missed can have a big impact on the calibration.

The best way to ensure you get the best out of your calibration is to read the manual and ensure that you understand what is trying to be achieved. The following tips will make sure you reach the next level:

• Always use the best Altitude Heading and Reference sensor (AHR) available – Our transceivers include onboard MEMS based Attitude Heading Reference sensors. Whilst these are great in locations where no other devices are available, a good quality GNSS derived heading sensor, FOG (Fibre Optic Gyro – such as a Sprint-Nav Mini) or LRG (Laser Ring Gyro – such as a SPRINT-Nav) will vastly improve the system performance.
• Update offsets – In order to get the best out of the calibration a good knowledge must be known of the transceiver to GNSS and the GNSS. Errors in these offsets can provide the largest errors of the calibration.
• Ensure your subsea beacon is suitably deployed – When carrying out the calibration, the required accuracy should determine the deployment method. For calibrations where ultimate accuracy is not required, a tripod mounted beacon is a good option. For calibrations where a lower accuracy is required, beacons deployed on strops and a float may be utilised. Stropped beacons will be able to move in currents and so will reduce the accuracy of the calibration but may be much easier to deploy and retrieve.
• Enter up to date sound velocity profiles – Sonardyne’s USBL calibration software has the ability to estimate the average sound velocity anywhere in the world throughout the year. This provides a good basis for the calibration however a recently measured sound velocity profile will provide the best result.
• Maintain good acoustic address discipline – Ensure that there is only one beacon in the local area with the acoustic address. If multiple beacons with the same address are within range the increase in noise will have a detrimental effect.
• Use the best correctional services available for your GNSS – The performance of the vessel GNSS will have a significant impact on the accuracy of the calibration. A simple GNSS solution will never result in a calibration of the same high accuracy of that as a GNSS with a real time correction service.
• Verify the new corrections – One of the most important steps is following the calibration. To ensure that no gross error has been made a verification run should be performed.

For more information on any of these notes please refer to the Ranger 2 manual.

A Gyro USBL contains an Attitude Heading Reference Sensor (AHRS) and a transceiver that is pre-calibrated. The Gyro USBL tightly coupled, pre-calibrated, meaning it’s portable and can be transferred from vessel to vessel without the need for calibration as the results are stored within the Gyro USBL itself.

This means only GPS offsets are required to be entered on installation. Eliminating lever arm offsets and any deployment pole or ship flexing between a separate AHRS and transceiver.

It is therefore possible to mount the Gyro USBL in any orientation to the vessel and the USBL tracking will be accurate to less than 0.1% of slant range, straight out the box. Perfect for vessel’s of opportunity.

On a ship with its own permanent heading device, it is best practice to align the transceiver in line with the rest of the vessel. This may not be possible to do physically, but you can use the Attitude/Heading Calibration option in Ranger 2 software.  You can find this option in the main menu under “Tools>Advanced”, use the ship’s sensors set as a reference point to estimate the alignment of the Gyro USBL to the ship.

Firstly, remember to enter the offsets for the ships gyro.

On completion, select “save to import”, results will automatically be entered in the “Ship to Lodestar” column in the offsets dialogue and your Gyro USBL will then be corrected to vessel frame.

A surveyor may wish to integrate a position into a survey desk or Inertial Navigation System (INS). A simple solution is to use an SSB as it is a widely accepted telegram. As well as inputting a raw Ultra Short BaseLine (USBL) position, the INS position may also be fed into a survey system. This article covers some basic scenarios to integrate with NaviPac.

Ranger 2 to Survey Desk:
To pass a position from Ranger 2 to a 3rd party survey desk, such as Eiva’s NaviPac 4, go to the telegram editor in Ranger 2 software and select an SSB_LBP telegram.
Select the beacon you require the position for:

• Frame of Reference = Ship, then it is possible to post process for a secondary GPS if required
• Orientation = North Up, because in ship frame any latency affects merging data based on vessel heading
• Source = Raw, so there are not 2 filters being applied

For a simple USBL job, in Navipac add a Dynamic Positioning Device to the Vessel and select the Kongsberg HiPAP/APOS driver. Click on the 1 button and select the vehicle the transponder is mounted on, in this case named “tow”. This links the beacon to the USBL on the Vessel.

On the Dynamic Positioning device on the subsea vehicle set the TP code to match the Ranger 2 index, in this case 1.

When the main vessel is configured correctly, you will be able to go online and in Eiva’s Helmsman the SSB position of the beacon will be displayed relative to the vessel.

Ranger 2 to INS:
All inertial navigation systems (INS) accept SSB inputs. In the Ranger 2 telegram editor, select the beacon you require the position for:

• Frame of Reference = World, INS systems require a Latitude and Longitude
• Source = SPRINT, the telegram is valid for the time of the transponder heard the interrogation, rather then when the transceiver heard the response

In SPRINT on the USBL LED input an SSB telegram, enter the offsets and select the Time Source.

From SPRINT to Survey Desk:
Most survey desks accept a GGA, however GGA only gives a position.

To only get position output add a GGA telegram from SPRINT and input to NaviPac 4 by adding a remote GPS point to the Subsea Vehicle.

If using NaviPac 4 use an LNAV output as this message contains position, depth, heading, pitch roll. NaviPac is able to share the same TCP port for gyro, motion, depth and input position on another port.

Contact [email protected] for more information.

Murky water, poor visibility, long tether? If you need to know where your ROV is in a challenging environment then have a look at this hints and tip video on how we would setup a Micro-Ranger 2 system to track an ROV.

Tracking Divers is one of the most common use cases for Micro-Ranger 2, but where do we recommend you mount the Nano Transponder? And how should the system be setup?

We have prepared a short video on the subject:

Accurate towfish tracking requires a USBL system to work well in shallow water at long layback and high elevation.

To add to the challenge, it needs to do all of this from a small vessel too. Micro-Ranger 2 has been designed to do exactly that. Its light weight and simple deployment means you can have the system installed and tracking towed targets within minutes.

In this short video, we’ll show you how easy it is to install the Micro-Ranger 2 system on our RIB.

Contact [email protected] for more information.

Ranger 2 has a rich graphical user interface, but when deployed on an unmanned or uncrewed vessel, we need another way to interact with it. That’s where the Remote Control feature comes in.

The Remote Control feature allows a third-party system to take control of Ranger 2 from a remote location using a lightweight yet intuitive and human-readable XML interface.

In this video, Chloe walks you through some of the features of the Remote Control interface.

Contact [email protected] for more information.

Ranger 2’s Marine Robotics Pack allows users to acoustically time synchronise systems onboard AUVs with a GNSS system on the surface.

Even the best clocks drift, and with the duration of AUV missions ever increasing, the need for a way to synchronise an AUV’s clocks to UTC during a mission led Sonardyne to create the Remote Time Sync Feature in Ranger 2. It’s now possible to remotely time synchronise a subsea clock to within 10 microseconds.

Tom demonstrates the Remote Time Sync features in this video.