One of the essential part of safe ships navigation and successful merchant fleet management system is implementation of appropriate ship tracking services. Satellite navigation and communication systems are used to track ships in oceans and cars on roads and off roads.
One of the great challenges of overseas navigation is the positional fix; what used to be done with a watch, an astrolabe and a sextant is now handled by high technology satellite systems, and rely on Einsteinian relativity for the time compression effects to make it work. As a whole, these systems are called Ship Tracking Systems, and most of them rely on GPS constellations.
A surface ship – whether a cargo hauler or a cruise ship – represents a significant investment, and depending on where your ship goes, that investment may be under risks for weather or piracy. Even without the insurance issues, there are other reasons for ship tracking systems, such as knowing when a given cargo will be delivered, or if a ship is going to be late to port with a perishable load. Ship tracking systems have progressed significantly since the 1980s, when public use GPS systems became available.
Most ship tracking systems use some combination of two satellite constellations; this gives redundant tracking arrays and the ability to correct for different orbital inclinations; the three most common constellations are the US GPS system, the higher resolution French system and the Iridium satellite telephone satellite constellation, which covers areas that aren’t covered thoroughly by the commercially accessible GPS constellations.
A GPS transceiver requires a signal from at least three and preferably four GPS satellites; these satellites have known orbital periods, and they broadcast a signal that identifies what satellite they came from, what their time was when broadcast, and a few other bits of information.
The receiver then compares the amount of time that those signals took to arrive from the three satellites and triangulates the position on a spherical coordinate system (of latitude and longitude). These signals are generally precise to within 10 meters with a three satellite fix, and within a meter with a four satellite fix.
A ship tracking system constantly relays these GPS fixes to a log, and then broadcasts that log (usually by satellite communications) every minute or so. This gives the people driving the ship accurate positional information (for comparison to charts of the sea and hazards, and weather information), as well as allows them to stay within dedicated navigation lanes, be aware of traffic that’s around them and so on. (In a lot of ways, cargo ship traffic isn’t that far off from highway traffic on icy roads – except that the collisions can be inevitable with more than 2 minutes of warning in some cases.)
When correlated with all the ships moving together, this can give an accurate fleet wide picture of where all ships are in relation to each other, and improves the safety of maritime operations. This also maintains schedules, helps identify mechanical problems and slowdowns and helps improve the overall operation of the shipping or cruise business.
Another great ship tracking service tool is Automatic Identification System (AIS) which is a short range coastal tracking system used on ships and by Vessel Traffic Services (VTS) for identifying and locating vessels by electronically exchanging data with other nearby ships and VTS stations. Information such as unique identification, position, course, and speed can be displayed on a screen or an ECDIS. AIS is intended to assist the vessel’s watchstanding officers and allow maritime authorities to track and monitor vessel movements.
More detailed information from personal experience as a daily AIS user in everyday job on VTS tower in next posts.
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