RE-ENGINEERING THE DNA OF A DVL

In 2007, Sonardyne surprised the industry by adding inertial navigation to its renowned acoustic positioning technology portfolio. Diversification into sonar imaging and optical communications quickly followed. Now, Sonardyne is entering the Doppler Velocity Log marketplace with ‘Syrinx’. So why has Sonardyne decided to develop its own DVL, what makes Syrinx unique and why should anyone invest in it? In search of answers to these questions, we spoke with the architects behind the new DVL, engineering directors Simon Partridge and Darryl Newborough, to get the inside track.

Question: So why introduce a DVL now?

Simon Partridge: “A Sonardyne DVL fills a small but very significant technology gap that currently exists in our extensive line-up of subsea positioning and navigation equipment. As a business, we are committed to the development and creation of innovative and exciting technologies. So from the outset, we were quietly confident that with the engineering experience within Sonardyne, a market leading product could and would be developed. And if initial test results are anything to go by, we weren’t wrong. Having an intimate understanding of the instrument allows us to provide the best possible subsea navigation solution using tightly integrated DVL, INS and 6G acoustics.”

Darryl Newborough: “Surprisingly there aren’t that many other DVLs out there, so users’ expectations have remained largely unchanged for years. However electronics and signal processing techniques have moved on considerably so we spotted an opportunity to re-set the performance benchmark.”

Question: So how did you approach the instrument’s development?

SP: “With a DVL, small velocity errors grow into larger position offsets with distance travelled, so it is critical in the development of a DVL that these small errors are minimised as much as possible. In this case, the devil really is in the fine detail.

As with anything from Sonardyne, when we set out down the development path, we aim to make it the best possible. We looked to the medical ultrasonics sector where billions has been spent on development, combining what we found with the best transducers manufactured in-house and the best signal processing; two areas where we excel. We also had to understand the fundamental physics, so we developed an advanced simulation and modelling capability to exercise candidate signals and signal processing architecture.”

Engineering directors Simon Partridge (left) and Darryl Newborough review the technological developments found within Syrinx.

DN: “We can essentially ‘fly’ our DVL in a 3D synthetic world and model the propagation of sound from Syrinx to the seabed and back again. This hugely helped in choosing beam widths, signals, electronics and processing techniques.We then ensured the software architecture was fully linear and highly configurable and finally ensured we could stream or log all raw acoustic data. This enables us to post process the raw data, including navigation sensor data, so trials data can be reprocessed and visualised to help in development. This has all led to what we believe are significant improvements in DVL precision and integrity.

In addition to the signal processing and environmental simulator improvements, the transducer design is critical to the performance of the DVL. To get the best performance, hundreds of hours of finite element modelling have been conducted with forensic material analysis to perfect the transducer design.”

Question: So how long has it been in development?

SP: “It has been in development behind the scenes for some years now as we did not want to rush things. We fully understand the commercial risk and technical pressures that are present in our markets so before releasing it, we wanted to make it the best product possible and ensure it was thoroughly developed and tested.”

DN: “The core architecture on which Syrinx is built is now validated, so engineering efforts can concentrate on optimising system performance, mechanical packaging and honing the user experience. DVLs are exposed to all sorts of abuse, so Syrinx naturally possesses all of the characteristics our transponders and transceivers are renowned for; compactness, ruggedness and robustness.”

Question: Who is Syrinx aimed at then?

 SP: “There are always horses for courses and this horse is aimed at providing class leading performance on ROVs, larger deep water AUVs and manned submersibles. It is not the smallest, but it is very important to understand that in this case, size matters. A DVL’s transducer size is set by frequency, beam width and performance in noise. The larger elements have narrower beams so more signal is focussed on the seabed and they are better at detecting the signal in the noise. So a bigger ‘head’ enables greater precision and higher altitude performance.”

Question: So how is Syrinx different to other DVLs?

DN: “Importantly Syrinx employs fully linear signal processing, unlike most DVLs in the market today. This enables the signal processing to be done in a different way.

The result is a 600 kHz DVL that operates both at high elevations and extremely low heights off the seabed. It provides very low noise, high precision velocity measurement in a wide range of seabed bottom types – rocks, mud, weed, steep drop-offs etc. The signals have been chosen very carefully to maintain bottom track and new algorithms ensure bottom ‘lock’ is always optimised – unlike other DVLs we tested which were prone to losing bottom track for some time.

We undertake everything in-house; the electronics, signal processing and transducer design, manufacturing, repair and support. Acoustically the performance is fantastic with excellent transducers and very low noise electronics.”

SP: “Syrinx has been designed and engineered for the offshore environment, one we have a real in-depth understanding of and market leadership position in. All the research into signal, transducer and electronic design adds up to a class-leading instrument with higher and lower altitude performance, high update rates and better resolution. The simple to use web browser interface provides access to configuration settings, diagnostics and data logging.”

Syrinx DVL Operating Range

The Syrinx 600 kHz DVL has been designed and developed to offer an altitude range that is comparable to a 300 kHz DVL, with the precision previously only achieved using a 1200 kHz DVL.

Question: So how has it been tested?

SP: “We’ve been using DVLs of different types for many years now to support the development of our subsea inertial navigation systems. We know when and why they go wrong. We know how to test them and that is against a high accuracy kinematic GPS aided INS on a vessel. Luckily we have the ideal setup and environment for this – our sea trials facility in Plymouth, UK. From here we have access to a very wide range of water depths and bottom types. There’s steep drop offs, whirl pools, flat muddy areas – you name it, we have it.

The results have been extremely encouraging. We have also tested Syrinx in our test tanks and at large flow tanks. We are highly confident about its class-leading precision. But precision is no good unless it has good integrity and reliability. So we have also done long term pressure and temperature testing that will continue to ensure we have class-leading reliability as well. The process has been thorough and exhaustive.”

DN: “Syrinx has also undergone independent comparative testing by a leading university in the UK, confirming class-leading performance. With Syrinx, you get the same precision as if from a high frequency DVL and the same high altitude performance as from a lower frequency DVL. It is essentially three sensors in one focussing on ROVs and the larger deeper water AUVs. In addition to the performance testing, the instrument is being tested to DNV 2.4 Environmental and EMC standard. This is extremely important as it ensures the instrument is reliable and will not interfere with other navigation equipment.”

Question: What other features set Syrinx apart?

SP: “Syrinx supports serial and Ethernet ports, a web browser interface, as well as the industry standard output telegrams, so it can be a straight replacement for existing units and hence easy to integrate into other INS systems. There are dual underwater connectors for reliability and flexibility and individual transducers can be replaced (not the whole array) if damaged. This significantly reduces repair bills.

DN: “From experience, the ability to log data and diagnostic information is extremely important when trying to attain the best possible performance. Software enables raw data to be reprocessed and visualised to optimise Syrinx for customers’ dedicated applications.

The instrument can store a lot of data that can be rapidly downloaded via the Ethernet connection using the embedded FTP server. The webserver makes it simple to configure using any PC with a web browser – so no PC software is required.”

Question: Does it link into other products you offer?

SP: “Certainly. Sonardyne is now the only company that make high accuracy acoustic positioning systems, inertial navigation systems (SPRINT) and a DVL under one roof. Coupling them together in the right way mechanically is an advantage, but tightly coupling them together at the data level enables a world of advantages that no one has properly explored yet. Getting all your subsea navigation technology from the same company also has tremendous commercial, service and support advantages for our customers.”

DN: “The ultimate performance differential of Syrinx will be realised when tightly coupled to our SPRINT INS. It’s a two-way relationship with Syrinx providing beam velocity data to SPRINT and in return, SPRINT aiding the DVL with information to ensure bottom lock is maintained even in the most difficult environments.”