Global Positioning
    System
 The System
 The Position Solution
 Hardware
 Ionospheric And
    Atmospheric Delays
 The Signals
 Dynamic Positioning
 Static Positioning
 Coordinate Systems
 Conclusions

Ionospheric and Atmospheric Delays

As we know the speed of light is a constant only in a vacuum, when light (or radio waves) travel through a denser medium the velocity decreases. The ionoshere is a band of electrically charged particles that slow down the incoming signals from GPS satellites. As our distance determination is based on assuming a constant speed of travel, this delay will affect the accuracy and precision of our positioning.

This 'error' can be reduced in the observations by using the time taken by signals using two different frequencies, or dual frequency receivers. The error in each will be different, and the on board processing functions of sophisticated receivers can eliminate this effect.

There are other sources of systematic and random errors that degrade the accuracies available from GPS positioning, however with advanced error modelling most of these can be eliminated.