Resilient PNT: Vision and Mission

Kurzfassung

A high-level user need recognized by the IMO is the resilient provision of position, navigation, and time data (PNT) to ship-side applications such as Automatic Identification System (AIS), Electronic Chart Display Information System (ECDIS) and Integrated Navigation System (INS). In order to avoid collisions and groundings, a reliable knowledge of ship’s position and movement in relation to other traffic participants is necessary and enables an improved situation awareness taking into account the own maneuver possibilities in relation to external geo-referenced conditions. The PNT data provision should be ensured for all phases of ships’ navigation such as ocean, coast, port and docking. Therefore different and increasing requirements on accuracy, integrity, continuity and availability of PNT data should be taken into account. Resilience describes the aimed ability of the PNT system to provide the PNT data with the required performance in case of internal and external disturbances. Typical examples of such disturbances are the vulnerability of GNSS or the occurrence of malfunctions and failures in applied sensors and services. Overarching objective of the PNT enhancement can be derived from the user needs “improvement of reliability” and “indication of reliability”. The current and desired reliability of the PNT system should be measurable to quantify the aimed improvement of reliability. For instance, in IMO A.915(22) the minimum requirements on future GNSS are specified for the horizontal position and given in terms of accuracy, integrity, continuity and availability. A comparable norm for all desired PNT data is still missing. A consolidated specification of desired PNT data and assigned technical requirements are prerequisites for the identification of technical gaps of the current PNT system as well as for the provision and assessment of suitable approaches to overcome the existing gaps. However, the greatest challenge on the maritime PNT system comes from the user need “indication of reliability”. Indication of reliability describes the desire that in future the accuracy and integrity of all navigation relevant data should be automatically assessed. Initial point for an automatic assessment is the complete and unambiguous performance specification of all required output data and assigned tasks. For this purpose the generally admitted processing chains for PNT data provision composed by GNSS, PNT relevant terrestrial services as well as additional ship-side sensors should be taken into account. In minimum the current status of contributing PNT subsystems should be comprised to estimate their residual influence on resilient PNT data provision. Nevertheless, an automatic assessment of accuracy and integrity requires the implementation of integrity monitoring functionalities on the one hand as well as the deployment of redundancy within the PNT system to enable integrity monitoring on the other hand. Due to the multi-system, multi-service and multi-sensor based architecture of the maritime PNT system the development of an overarching integrity concept should be aimed. Such an integrity concept regulates responsibilities of single subsystems for integrity monitoring, identifies the minimum on redundancy and specifies additional interfaces to ensure the integrity messaging in an unambiguous manner. Regarding safety the integrity concept supports that the achieved and desired level of reliability will be measurable and specificable. Furthermore the tolerable residual risk of resilient PNT data provision (incidents) can be distributed on contributing components and can be optimised among them. Otherwise, approaches to improve critical components or to overcome gaps will be rateable regarding their benefits. The paper presents an initial guideline for the development and establishment of an Integrated PNT System to meet identified user needs in the future.