Plain English Meaning

GPS signals slow down a little when they pass through a charged layer high in the atmosphere. That slowdown makes the receiver think the satellite is farther away than it really is, so the position it shows is slightly off.

Full Definition

Errors in GPS position fixes caused by the slowing of satellite radio signals as they pass through the ionosphere, the electrically charged layer of the upper atmosphere. Because the signal travels slightly slower than it would through a vacuum, the receiver calculates the satellite as being farther away than it actually is, introducing a range error that affects position accuracy.

Context Anchor

Seen in GPS error discussions, especially when learning why satellite navigation is not perfectly accurate under all .