chapter  18
5 GPS signals
Pages 2

Selective availability (SA) is a feature of GPS

that intentionally introduces errors (typically 10

meters horizontally, and 30 meters vertically) into

the publicly available L1 signals. This is a

political strategy that denies any advantage for

hostile forces acting against the USA. The highest

GPS accuracy was available (in an encrypted

form) for the US military, its allies and US

government users. During the 1990s, a number of

political factors were mounting in the USA:

• The shortage of military standard GPS

ground navigation aids with GPS.