ABSTRACT
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.
