Using PNT Integrity Information for a Maritime Traffic Alert and Collision Avoidance System

Ralf Ziebold, Christian Denker
Currently mariners on merchant vessels are supported by driver assistant functionalities while navi-gating like e.g. a track pilot. Here a vessel follows almost automatically a predefined track. For a safe journey the track pilot requires a travelling path free of vessels or other obstacles, which also appear dynamically on vessel’s path. A powerful driver assistant functionality, supporting the mariner for collision avoidance, is currently missing. Within the 3-year Project MTCAS, partners from industry and academia contribute to accident reduction by developing an e-Navigation based System for pro-active, predictive and cooperative collision avoidance. MTCAS is the abbreviation for Maritime Traffic Alert and Collision Avoidance System, which implies the basic idea of adopting the Airborne Collision Avoidance System (ACAS) implementation TCAS. However, MTCAS’ operational principal aims at enabling the team on ship’s navigational bridge in conflict detection and conflict resolution under consideration of the concrete ship’s environment. Concrete examples include regularities, bathometry, non-equipped vessels and Vessel Traffic Services (VTS). Different from TCAS, MTCAS does not automatically intervene in terms of issuing steering commands, but moreover supports seafarers in cooperatively finding safe and efficient trajectories, which is completely different – innovative – compared to the basic TCAS purpose.In this paper the basic MTCAS concept with its onboard and shore side components will be introduced. Concretely the paper will focus on the onboard sensors, which are required for such a safety of life critical assistant functionality. The collision avoidance system in aviation is mainly based on altitude measurements and a resolution advisory is given to climb or descent for both airplanes in a coordinated manner. The altitude is determined mainly by very simple and robust air pressure sensors. Additionally only altitude differences are of importance and therefore systematic errors like the nominal air pressure are canceled out. This simple approach of climbing and descending however can’t be used for a maritime TCAS, due to the missing third degree of freedom in surface vessel navigation. Therefore the maritime collision avoidance needs to be performed on a horizontal plane only. As possible sensors the marine RADAR, which provides relative distance and bearing of an object, and absolute, GNSS based Position Navigation and Timing (PNT) information can be used. Especially in constrained waters, with limited maneuvering space, the usage of absolute positioning is necessary.Currently Global Navigation Satellite Systems are already the main source onboard determination of position, velocity and timing information. However the usage of this information for safety of life critical applications like MTCAS is currently not possible due to the lack of integrity. In order to overcome this gap, the German Aerospace Center was actively contributing to the development of new ‘Guidelines for shipborne position, navigation and timing (PNT) data processing’, which have been now finally adopted by IMO’s Maritime Safety Committee (MSC) in June 2017. The main benefit of these Guidelines is the provision of a framework for standardized provision of PNT data and associated integrity and status information which will in future enable safety of life critical applications.The German Aerospace Center has developed a prototype of a PNT data processing unit, which is based on the combined usage of GNSS and onboard sensors like speed log and inertial sensors in a multi sensor fusion scheme. This system provides PNT data with the associated integrity information for the absolute horizontal position, velocity (speed over ground, course over ground) and orientation (heading, roll, pitch) of the vessel.In the MTCAS project a preliminary interface has been defined in order to transmit the PNT + integrity information to the MTCAS assistant functionality. The paper will in detail describe how the PNT integrity information is used inside the MTCAS collision detection functionality especially for the reliable assessment of the risk of collision.
10 / 2018
Maritime Traffic Alert and Collision Avoidance System