Accurate Position is an integral part of piloting ships especially during confined navigation or critical manoeuvres such as berthing/docking, passing locks, narrow channels or ship-to-ship transfer operations.
Conditional to the level of independence sought from the ships’ own data, position can either be derived from the ships’ AIS with Pilot Plug based PPU’s like the GyroPilot or it can be derived from Satellite (GNSS) positioning data from PPU’s like the GyroPilot Plus, ChannelPilot and HarbourPilot.
Raw position derived from GNSS satellites is usually accurate to under 2m. While this level of accuracy works to support some manoeuvres, other ship-handling operations require higher position accuracy data.
Corrections can be applied to GNSS receivers to improve their accuracy.
These are derived from ground-based Base Stations which observe differences in calculated position (caused by atmospheric interference and timing errors) and deliver these to GNSS receivers in the following methods.
Ground based corrections technologies like RTK and DGPS require shore-based infrastructure (either single base stations or an array or Continually Operating Reference Stations (CORS network)) to be employed. These base stations must be installed at surveyed locations and could be limited in their range due to transmission protocols and receiver types. With DGPS position accuracy can be <60cm and RTK position accuracy can be <1cm.
To overcome the range issues, corrections are also sent via Satellite Based Augmentation Services (SBAS). These are freely available satellite based correction technology, made available by various countries but is normally limited in its footprint (to the country it is launched from). These geostationary satellites provide corrections to augment the navigation information coming from the orbiting GNSS satellites. With SBAS, position accuracy can be corrected to sub-metre levels.
Privately owned correction services also exist and are available on annual subscription packages. Major players are Fugro, Trimble and Hemisphere.
Navicom Dynamics Portable Pilot Units incorporate these technologies in our products to provide users with the precise position data required to achieve expert levels of navigation. Contact us to discuss how these are best suited to your needs.