- Availability of accurate position determination (SATNAV);

- On-board navigation data management (interfacing);

- Availability of exclusive VHF channels (ITU);

- International carriage requirements (SOLAS Chapter V);

- Display on integrated units (radar/ARPA, ECDIS);

- International standardization (ITU);

- Integrity monitoring.

3. Advantages of DGPS/"Transponder" Tracking vs. Radar Tracking

The benefits of radar and ARPA with respect to both navigation and collision avoidance are enormuous. However, the detection, acquisition and tracking of radar targets on-board of ships and within VTS is limited by some well-known physical problems and constraints related to clutter, shadowing of targets, discrimination accuracy, processing delay, target swap etc. These constraints can be overcome by "Transponders". As DGPS positions are more accurate than radar positions, there are significant advantages of DGPS/"Transponder" tracking compared to radar tracking:

3.1 Additional relevant information

- Active Identification

- Heading, type and status of ship ("fishing vessel", "not-under-command" etc.);

3.2 Improved tracking

- Increased coverage (outside the normal radar coverage)

- Detection of targets with small cross sections

- Easy detection in clutter

- No shadowing of targets

- No unrealistic centres of reflection

- No "goest echoes"

- Improved accuracy and discrimination

- Improved actuality of ship's data

- Reduction of target swaps;

3.3 Back-up of radar information

- Reparation and improvement of radar tracks

- Replacement of radar tracking.

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