Laser position reference sensor ensures redundancy

Figure 1 shows that the CyScan GeoLock sensor has received five reflections and has found a reflection match for all the surveyed reflectors leading to a valid position reference being produced. The fifth reflection is spurious and not used by the system.

Incomplete match example

Figure 2 shows the CyScan GeoLock sensor has received five reflections and attempted to match their pattern against the pattern of the four surveyed reflectors. Three of the reflections match the pattern of three of the reflectors while the other two reflections are considered spurious and are not used. The fourth reflector is not observed/matched but three matches are sufficient in this instance to provide a position reference.

CyScan GeoLock uses a combination of an external GNSS input and the reflector matching algorithm in place of the DPO to

• Determine the constellation to choose for matching the detected reflector positions.
• Decide when to autonomously (re)start the sensor and initiate tracking.

The reliance on GNSS input to provide redundancy against GNSS failure is a point for concern. However, CyScan GeoLock only makes limited use of the GNSS to notify the sensor which constellation should be used to match reflections against. This means the accuracy of the GNSS fix required is very low and knowing the position to within 100 m is acceptable. In addition, GNSS accuracy is most reliable in open water where shadowing and multipath effects are limited, although this can be compromised in more congested conditions.

After this initial successful trial, a CyScan GeoLock sensor was mounted on board the Folgefonn car ferry, which operates between the Jektevik, Hodnanes and Huglo ferry terminals in Norway.

The aim of the Folgefonn trial was to demonstrate and trial the Wärtsilä DP Auto Docking & Transit system with CyScan GeoLock as an additional PRS for redundancy purposes. The Folgefonn trial successfully demonstrated both the Auto Docking system and CyScan GeoLock sensor during several hours of continuous autonomous operation. To facilitate operation, three reflectors (CyScan AS Prisms) were installed at the Jektevik ferry for the vessel’s Jektevik approach and departure.

Autodocking has successfully been demonstrated and using CyScan GeoLock ensures redundancy and non-reliance on DGPS which is prone to jamming/spoofing. This has given the vessel owners and authorities confidence in the reliability of the system.