Advanced GNSS+Inertial for marine survey and dynamic positioning

Ship with superimposed beam-like graphics

The world’s seas and oceans offer a wealth of untapped resources, yet are little known: Only about 15% of the global ocean has been mapped by modern survey systems to provide detailed information about the seafloor. Deeply integrating GNSS and inertial positioning, SPAN technology from Hexagon | NovAtel provides highly accurate real-time attitude data to compensate for the pitch/roll motion of vessels. This yields six degrees of freedom (DOF) observations critical for high-resolution mapping.

The international community has made a huge investment in ocean science to create a global chart of the seabed of requisite quality and accuracy for research and many different applications. The United Nations has proclaimed a Decade of Ocean Science for Sustainable Development (2021-2030).

In the oil and gas industry, for just one example, companies seek to understand the seabed from a topography point of view, to know if a pipeline route is clear of obstacles and unexploded ordinance. 

Once rich undersea deposits of oil and gas have been located, SPAN technology continues to play a key role. Deep-sea drilling, transport of materials to and from oil rigs, underwater construction and infrastructure maintenance and other activities all require marine vessels that can hold a safe and stable position on the ocean’s surface. The high cost of any operational downtime, as well as the inherent risks associated with marine operations, mean that robust and reliable positioning, particularly in obstructed environments such as adjacent to offshore platforms, is critical to the industry.

Hexagon | VERIPOS delivers positioning solutions that are critical for all operations as they provide the accurate georeferenced position required for mapping and dynamic positioning (DP) applications. Speaking to Velocity magazine, David Russell, Marine Segment Manager, Hexagon | VERIPOS, said, “Deeply coupled SPAN technology allows us to access the raw GNSS and IMU observations to deliver a robust and reliable integrated solution, bringing together the best of both technologies.”

Vessels involved in deep-water drilling are expensive assets to operate. Sustained accurate positioning forms a critical component in what they do. Downtime and any other result of interruption or inaccuracy are extremely costly.

“At VERIPOS, we create positioning solutions that feed into onboard dynamic positioning systems,” Russell said. DP is a control system on a marine vessel which use inputs such as position to control the output of the thrusters to maintain station over a location.

“DP is a form of autonomy,” Russell said, “where the vessel is basically operating itself, taking information from a number of sensors, including positioning, into the control system to ensure that the vessel automatically maintains position over a location with minimal operator input.

“What we’re providing to these operators is a complete positioning solution. This includes GNSS correction services, the hardware to receive the correction services and all the satellite signals, and then software to provide visualisation of that. We use GNSS cards from NovAtel in VERIPOS hardware and the SPAN GNSS+INS technology combines GNSS satellite positioning with inertial navigation system (INS) measurements from inertial measurement units (IMUs).”

VERIPOS also provides installation and 24/7 support to ensure reliable and continuous operations.

Surveying for sustainability

Hydrographic mapping creates charts of the seabed that are very much in need today. The so-called Blue Economy has a far bigger research focus than just oil and gas. Other industries now have= the budgets for high-quality mapping. This includes nearshore installations, port dredging, windfarms and more. Finally, the autonomous survey vessels operating at sea, collecting data for these clients, form an industry all by themselves.

“Our first applications were in oil and gas survey applications which were creating maps of the seabed for planning or construction activities.”

Overall, sustainability is a watchword, with autonomous ships and seabed mapping an integral part of all sustainable efforts. 

“Hydrography is looking for position and attitude data with higher accuracy compared to DP. They also want to log all the raw GNSS and IMU data so it could be re-processed later if required. Clients can go back and reprocess the raw data. They’re looking for a lot more data to help them process everything.”

Yaw, pitch and roll data, as well as heave data that reflects the motion of the vessel are required for hydrography. 

VERIPOS, whether for DP or hydrographic survey, supplies the same system but in a different configuration on the vessel.

“Surveyors are more interested in data quality and accuracy,” Russell continued, “to allow them to geo-reference all the sensor data they gather such as multibeam so that an accurate chart of the seabed can be created.”

This particular integration is built exclusively for VERIPOS. Purpose built, it has the best-in-class sensors that, when combined with the firmware and algorithms, deliver best-in-class hydrographic solutions.

“NovAtel could supply any number of other OEM packages,” Russell said, “but VERIPOS has taken the most desirable different bits and put them into a package that can be used in different parts of the marine industry.

“We use a deeply coupled solution, not many people have that in the market. SPAN technology is a proven solution, has been around a while; now we’ve brought it into the marine market for hydrographic applications.”

Shoring up maritime DP

All modern vessels of the type used in offshore oil and gas operations come from the shipyard with DP. “It’s part of the build requirement,” Russell explained. “DP systems are made to take in all kinds of information, including GNSS positioning but also wind, radar, laser measurements and other sensor and environmental data. This then provides the output that tells the thrusters what to do.”

GNSS-only positioning becomes unreliable or impossible when satellites are blocked by physical obstructions. In the maritime domain, this can be caused by massive offshore rigs. Other kinds of interference, intended or unintended, can also compromise GNSS positioning. SPAN technology from NovAtel provides continuous 3D positioning, velocity and attitude determination, even when GNSS signals are compromised for short periods of time. It does so by integrating industry-leading GNSS technology with inertial measurement units (IMUs) to create a deeply coupled GNSS+INS solution. With deeply coupled measurements, a user can maintain continuous operation and 3D positioning while also achieving rapid signal reacquisition when a GNSS signal is lost and a high resistance to interference and jamming.

When combined, GNSS and IMU augment and enhance each other; the absolute position and velocity accuracy of the GNSS can be used to compensate for errors in IMU measurements. The stable relative position of the INS can then be used to fill in the gap when the GNSS solution is degraded or unavailable.

NovAtel fields a range of solutions to support robust positioning. In addition to SPAN technology, GPS Anti-Jam Technology (GAJT) is a commercial off-the-shelf GPS solution easily integratable with existing receivers and vessel navigation systems. GNSS Resilience and Integrity Technology (GRIT) is a firmware suite for NovAtel receivers to expand situation awareness and interference mitigation tools across applications and environments, protecting against GNSS interference.

NovAtel SPAN technology

“When we talk about SPAN technology, and when we use that term deeply coupled, this means we’re doing everything at the measurement level,” Russell said. “We have access to the raw GNSS information, and we’re actually using that to drive our integrated solution. That’s what we feed into the positioning algorithms, and the end result is improved robustness.”

The ability to access raw GNSS measurements allows deeply coupled SPAN technology to use data from even partial GNSS constellations to improve INS positioning. This is especially valuable when GNSS is partially obstructed. It enables precise relative updates from GNSS measurements in addition to the absolute, but sometimes noisier, positions. Deep coupling also incorporates INS filter information to aid in GNSS acquisition and tracking for more rapid reacquisition time.

Deeply coupled SPAN technology is highly resistant to jamming, as well as to unintended interference from other communication systems. It confers robustness against time-limited signal blockage by large structures. It features stabilized signal tracking in low signal-to-noise ratio (SNR) scenarios and displays admirable insensitivity in high-dynamic situations.

“With our SPAN technology, you’re not relying solely on a GNSS PNT solution,” Russell said. “As long as you’ve got a couple of raw measurements going up to the inertial filter, that will help constrain the drift of the inertial solution, so the advantage is about the robustness and reliability that you can derive from all of the combined data. This gives you better position availability and minimises downtime. From a cost perspective, that means the vessel can operate with fewer interruptions.

“Another concern for vessel operators is of course safety,” Russell said. “You have diving operations, for example, where you’ve got people in the water. Here again you’re looking to maximise the positioning availability and reliability to make sure that everything’s robust. You don’t want to lose position and have the vessel moving off the location that may put divers in danger. You don’t want to see GNSS outages that might cause position runoffs or position jumps. “It’s a similar story with subsea construction. In order to extract the hydrocarbons, you actually have to build infrastructure down on the seabed. You might be talking about divers or you might be talking about remotely operated vehicles [ROVs] or other equipment. There is a move to unmanned vessels, which need a more robust level of positioning to ensure they can operate safely without any crew.

Complete positioning solutions

VERIPOS incorporates SPAN technology from NovAtel in its own proprietary positioning solutions. The VERIPOS LD900, for example, has an integrated component featuring one of NovAtel’s OEM7 series of positioning engines. The LD900 is a quad-band GNSS receiver, capable of tracking GPS, GLONASS, BeiDou, Galileo and QZSS constellations. It receives L-Band signals on multiple channels, providing access to the world-wide independent correction links and services provided by VERIPOS. “We have the LD900 but also the LD8,” Russell said, “which are our main units. Both are using SPAN technology with NovAtel’s OEM7700 or OEM7720 GNSS boards.” 

VERIPOS positioning solutions for DP also include highly robust correction services. “We offer three levels of correction services,” Russell said. “We have APEX, which is our own correction service, where we control all the algorithms. We build it.” Apex uses PPP, an absolute positioning technique that corrects or models all GNSS error sources, including satellite orbit and clocks, tropospheric, ionospheric and multipath errors. PPP isn’t dependent on the location of reference stations, so it’s able to provide position accuracy regardless of location.

VERIPOS operates its own orbit and clock determination system (OCDS), which derives real-time corrections for all available satellite constellations using proprietary algorithms. The OCDS uses data from VERIPOS’ own reference station network. These stations are independent from the reference stations used by JPL for VERIPOS’ Ultra services.

“The market is asking for independence and redundancy, so we offer a second PPP correction service; that’s our Ultra service, which is derived from the JPL network. And then as a backup to all that we still offer differential corrections from a set of reference stations. There are people that still want that as a backup, so again it’s back to having maximum redundancy and availability to ensure that you can keep on operating and that you’re also operating in a safe way.

“The companies we work with are involved in all aspects of oil and gas exploration from marine seismic and deepwater drilling through to construction, field maintenance and ultimately de-commissioning.”

These are operators that must make enormous investment commitments in a given project, and they depend on VERIPOS systems to deliver at competitive prices. Efficiency and safety performance are among their key priorities.

Digitalisation drives survey

“The standard buzzword in the marine industry nowadays is digitalisation,” Russell continued. “Digital technologies are being used to increase competitiveness and improved operation efficiency. High bandwidth and two-way data communications will be the key to digitalisation, but also remote or autonomous operations in the marine industry.”

That’s where the market is going. “New data communications could also lead to changes in how or where the data is processed given there may be no crew on the vessel.”

Safe passage

VERIPOS has come a long way since its beginnings in 1989, when it was formed as a joint venture between Brown & Root Survey and Ormston Technology, operating a high-frequency differential GPS network in the North Sea. Russell joined VERIPOS in 2003 when it was still a regional player based in Aberdeen. Hexagon acquired VERIPOS in 2014, and it is now part of Hexagon’s Autonomy & Positioning division along with NovAtel. As part of Hexagon, VERIPOS has access to and influence over the development of a wide range of GNSS solutions and hardware, as well as technology used for other markets, such as GAJT and GRIT.

VERIPOS has become a significant global player in the maritime positioning market, leveraging SPAN technology from NovAtel and its own proprietary corrections network to deliver state-of-the-art differential global positioning on the high seas. “We’ve been involved in offshore marine positioning for a long time,” Russell said. “In that time we’ve seen satellite navigation technologies enable new solutions that have replaced legacy terrestrial navigation systems such as Shoran, Syledis and Pulse-8.

“The industry was an early adopter of GPS and GNSS,” Russell said. “The main restrictions in the early days were satellite availability and channel limitations of the receiver hardware. Though it was expensive, GNSS positioning was still cheaper than the other systems being used.” 

Today, GPS and now GNSS are so integrated and key to vessel operations with the kind of accuracy that’s routinely achievable, our users are now less interested in accuracy. The focus has shifted toward reliable and robust positioning to minimise operational downtime.

“Our customers in oil and gas don’t want to have to do an emergency disconnect from a well, which is why why our market is heavily focused on safety.”

Russell said VERIPOS will continue to work with customers to determine their requirements. “Our aim continues to be to identify new technologies and opportunities with GNSS, the things we can do with advanced technologies like SPAN technology and deep coupling, to develop the solutions our customers want and need.”

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