A Decision Support Framework for Collision Avoidance of Unmanned Maritime Vehicles - Intelligent Computing for Sustainable Energy and Environment - page 554

assist the risk assessment. The results illustrate a scenario of two dynamic ships with
paths which are orthogonal to own ship's heading. Both the vessels are travelling
opposite to each other at a different range to the own ship. Hence the own ship,
according to the maritime rules, becomes a give-way vessel to the ship on its
starboard whereas it will act as the stand-on vehicle to the ship on its port-side. The
risk assessment unit determines this accordingly and may issue a recommended action
to the captain/autopilot in addition to providing feedback to the path planner.

Fig. 2. Detecting multiple dynamic ships by the obstacle detection and identification subsystem.

4.1 Detection of Obstacles

Fig. 2 shows a snapshot of one of the simulation scenarios. As shown, the obstacle
detection and identification subsystem has successfully detected the two cruisers
present in the scene in real-time. This is shown in the form of rectangles or bounding
boxes around the target vessels. Also note that the improved background subtraction
technique ignores the dynamic waves in the scene which otherwise be detected as
several moving objects. Once an obstacle is detected and its states estimated, the
information is displayed on the virtual map to assist the remote human operator or the
captain of a manned ship. This virtual mapping system also displays suitable actions
that are either being taken or recommended by the risk assessment module. The
following subsection will further elaborate on this.

4.2 Multiple Dynamic Obstacles Avoidance Scenario

The pan and tilt platform is employed to periodically scan in the vicinity of the USV.
This provides an alternative to a radar but at a lower cost. Moreover, the system is
able to detect close-range obstacles which may pose a direct threat to own ship for
which reactive path planning may become necessary. Fig. 3 depicts the processed data
on the virtual map of the environment developed as part of the proposed system. This
is analogous to a radar screen as explained earlier. However, this virtual map only
displays the information around the USV in a 180o span and continually update as the