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Author Topic: Why might a GPS device display differing heights during a sea voyage?  (Read 2753 times)

Offline siasl

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Sea voyage on the same body of water - tidal effects discounted from the cause of this phenomena

Offline robinsamuels

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Bloody great waves?

Offline siasl

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calm sea :P

Offline robinsamuels

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Travel near the poles?

Offline Blacksmith81

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The Earth is not a true sphere, it's squished at the poles and bulges out towards the Equator.

For the sake of simplicity, GPS devices have been programmed to represent the Earth as a sphere, using a mean surface level as the datum. This will give rise to an apparent gain or loss of altitude, displayed on the device, with any displacement in a North-South direction.
« Last Edit: 14 March, 2009, 08:25:11 AM by Blacksmith81 »

Offline moonzero2

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I'm not sure if this is the case now but plane altimeters had to be re calibrated when flying over water, this was to do with differences in air pressure which occurs over large areas of water.

Just possibly, it may have an effect on the high frequencies used in gps signals.
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