Why three or more satellite needed? GPS error.

Why three or more satellite needed? GPS error.

Why three or more satellite needed?
GPS works on Principle of range measurement.
Range measured by GPS receiver is not true range but pseudo range. Pseudo range contain user clock error.
If exact time is known then,
Only one range will give spherical shell of position. But two range intersection will place observer on a circle. Three range intersection will place observer on two possible position. But four range from four satellite will give exact position.
3 satellite give 2D fixing
4 satellite give 3D fixing

GPS error in open sea or ocean
Range inaccuracy
Wrong data from satellite
Satellite may fail
Satellite out of sight

GPS error in Coastal area
Range inaccuracy, so GPS not reliable in Coastal area
Wrong data from satellite
Satellite may fail
Multipath error due to shore object
In restricted visibility GPS signal may be disturbed, so it is dangerous while in Coastal area

Published by

KRP

Mr. KRP is the founder of sailorsknowit.com, he has a great experience about life at sea. You can get in touch with him by email at info@sailorsknowit.com