GNSS-Denied Navigation and Training

Lars Klemmetsby, Vice President Business Development Defence, Kongsberg Digital, and Axel Törneman, CEO, Seacross Marine, explain how their combined product portfolios offer a unique solution for fast craft navigation training in challenging, GNSS-denied environments.

The use of Global Navigation Satellite Systems (GNSS) has revolutionized maritime navigation. Most mariners have become dependent on GPS and other GNSS-based navigation systems and the high-precision positioning, navigation and timing (PNT) services these applications provide. With this development the requirements for in-depth knowledge about these systems’ shortcomings and the ability to maintain efficient and safe navigation even in GNSS-denied environments are becoming increasingly more important, for military navigators in particular. The combined product portfolios of Kongsberg Digital AS and SeaCross Marine AB represent a unique end-to-end solution for high-speed navigation and simulator training that prepare and enable fast craft navigators to operate efficiently in environments where the navigation system’s sensor input is lost or degraded by intentional or unintentional GNSS interference. 

Military vessels are expected to operate with short reaction times and at high speed in the most challenging waters, and in all environmental conditions. Modern naval vessels are equipped with advanced sensors and integrated navigation systems that allow for high-speed operations in the most demanding areas of operation. As the majority of the onboard systems are dependent on GNSS input, the bridge team must be fully aware of their shortcomings. GNSS may be denied by attacks on the space or ground segments of the system, by jamming of the signals available at the vessel’s receiver or as the result of signal blockage or signal multipathing. A military navigator must therefore have the skillset and knowledge to quickly identify when the navigation system’s accuracy is being degraded and swiftly transition to the use of alternative navigation techniques to maintain efficient navigation and mission progress in a GNSS-denied environment. To be able to achieve this, in-depth navigation system knowledge and mastery of visual and manual navigation techniques are equally important.

By combining the solutions from KONGSBERG and SeaCross, an end-to-end concept for high-speed navigation and simulator training that prepares and enables fast craft navigators to operate efficiently in environments where the navigation system’s GNSS input is lost or degraded can be offered. The training aspect is comprehensively covered by Kongsberg Digital’s K-Sim Fast Craft Simulator technology. Designed to provide trainees with a realistic perception of operating in a real-life environment, the simulator utilizes an advanced physics engine, motion system and hydrodynamic vessel modelling capabilities to replicate the behavior of high-speed vessels in various sea states and at all speeds. A complete replication of the actual vessel’s operator positions, with integration of navigation systems and onboard equipment, allows the fast craft operators to perform efficient, safe and repeatable training and mission rehearsal in a virtual environment.

Born in Scandinavia, the SeaCross navigation system’s capabilities are based on extensive experience and knowledge derived from operating high-speed craft in exceptionally demanding Nordic environments. The system is created, designed and developed to offer unparalleled short Process of Navigation latency and safety for high-speed navigation. The SeaCross navigation system is modular and scalable, designed to meet the requirements for high-speed operations in archipelago, littoral, coastal and open waters. The navigation system is typically used on board vessels operated by special forces, naval high-speed units, police, fire fighters and SAR units.

Functionalities designed and developed to support GNSS-denied navigation are incorporated as standard features in the SeaCross system. These features offer Estimated Position and/or Dead Reckoning (EP/DR), based on any combination of passive sensor input, heading and speed through the water, plus manual navigator data input, allowing continued high-speed navigation under circumstances when GNSS sensor input is not valid or corrupted. When spoofing, jamming or other sensor failures cause loss of data, the navigation system routinely switches to EP mode. In this mode, SeaCross uses the best available sensor input at any time to analyze position, speed and heading from a combination of instrument and/or manual operator input. EP mode can also be activated on operator command. The displacement errors accumulated by EP/DR over time can be instantly corrected by the navigator on the fly using input from the radar’s non-terrestrial object enhancement function or by using the inbuilt Line Of Position and Running Fix functionality.

The Kongsberg simulator supports fault settings on device, sensor and panel levels. This allows the instructor to create degraded navigation system conditions by inducing faults, to train navigators in identifying failures and inaccuracy of the navigation equipment. The instructor’s fault settings manipulate the actual values which are used by all the systems in the simulator. The instructor can monitor the difference between the clean (unmanipulated value) and dirty (manipulated value) during the operation. With this flexibility, the instructor can introduce degraded subsystem and simulated failures caused by different types of sensor denial.

In K-Sim Fast Craft the GNSS includes position reference calculations based on the realistic movement of 24 satellites in six satellite planes. The Signal-to-Noise ratio (SNR) is calculated for each satellite based on the elevation from the receiver to the satellite, and a spectrum is presented to the instructor to monitor the resulting SNR values. The instructor is able to override the SNR for each satellite by adjusting the signal bar as desired. Satellites with SNR above 30 are used for position fixing. If the Instructor reduces the SNR, the GNSS accuracy will be affected and a dilution of precision (DOP) value will be calculated. The SNR spectrum is presented on the GNSS instrument itself to monitor GNSS position output, and it is possible to disable individual satellites on the GNSS instrument to eliminate noisy signals. To simulate further degradations of the navigation system, the received position data can be altered as follows:

The focus of the partnership platform between KONGSBERG and SeaCross is to develop unique and effective products and end-to-end solutions for high-speed navigation and fast craft simulation by utilizing the joint strength of the two companies. The platform comprises a chain of building blocks for training, simulation, planning, mission rehearsal / validation, real world navigation and de-briefing:

System operator training can be done individually on standard laptops using SeaCross E-Learning packages, or supervised and managed by an instructor for single or multiple users.

The K-Sim Fast Craft simulator, with full integration of the SeaCross navigation system and control units as used on-board, offers the realistic training environment needed to support the full spectrum of high-speed navigation. The students can operate the SeaCross navigation system in the simulated environment and use the methods and navigation techniques needed to determine and monitor the ship’s position by the use of visual and electronic means. This includes visual bearings to navigation aids, landmarks, buildings and other objects in the visual scene. These visual bearings can be supplemented with data obtained from other sensors such as echo sounder or radar and used as inputs to the SeaCross system in a GNSS-denied scenario. The RADAR system can be used to plot a position by taking the range and bearing to a fixed and known position in the radar view.

The planning stations(s) are used for pre-mission preparations such as route planning, creation of customized mission-oriented templates or for sea chart updates and distribution. The planned mission can then be validated and rehearsed in the simulator prior to mission execution.

While under way all sensor data, including radar and operator interactions, can be recorded to a standard removable file. A recording can be replayed, allowing the Simulator to be used for debriefing purposes. Recordings from multiple vessels can be replayed concurrently, offering an opportunity to re-enact missions involving more than one craft. All SeaCross navigation systems can record available onboard sensor data including radar. Recordings from one or several vessels can be loaded, post-mission, into the Simulator and replayed concurrently for de-briefing and training purposes.