Global Positioning System GPS

GPS supplies accurate three-dimensional fixes 24 hours a day, in all weathers, anywhere in the world, even though for maritime purposes, two dimensions will do very nicely. The system in general use in 2005 is operated by the US military establishment, although independent equivalents are just over the horizon. Given that your set does not break down, there is only one catch: in order to preserve US national security, those in charge of GPS are 'dedicated to the development and deployment of regional denial capabilities in lieu of global degradation'. This means that rather than downgrade the signals globally or turn off the satellites completely, sensitive areas can be blacked out from GPS signals.

A constellation of 21 satellites has been arranged in a 'birdcage' around the Earth, together with 3 stand-by 'spares'. Their extremely high altitude keeps them clear of skywaves and other atmospheric interference. It also guarantees that four or more can be seen from a given location at any time. The system is completed by various control and monitor stations around the world. These maintain system accuracy, together with other forms of monitoring and updating of the navigation message of each satellite.

GPS works by knowing the satellites' position in space. Each of them transmits coded data which include a radio signal timed to mind-numbing accuracy. This enables the receiver to calculate the distance of the transmitting satellite from its antenna, which gives it its position on the surface of a sphere centred at the satellite. The receiver chooses the three or more satellites offering the best 'cut' of position lines (position spheres in reality) and works out its position from these (Fig 19.1).

How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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