President Turns Off GPS Selective Availability (SA)
In 1998 U.S. President Clinton made the order that, between the years of 2000 and 2006 the GPS Selective Availability should be turned off. This went into effect very early, at midnight on May 1st, 2000, EDT; and on May 2nd, 2000, civilians all over the world noticed that their GPS receivers were much more accurate than the day before.
By scrambling the signals from the GPS satellites, Selective Availability added up 100 meter random errors (approximately 300 feet) to civilian GPS readings. This was in order to keep GPS as a more powerful tool for the military. Now the military can selectively block GPS transmissions in areas of the world in which there is conflict.
Turning off Selective Availability greatly improved GPS for civilians in all walks of life; e.g. basic car navigation, taxi-cab fleet management, commercial trucks, buses, rental cars, delivery services, emergency vehicles, aviation, commercial fishing, boating, highway and waterway maintenance, roadside assistance, wildlife tracking, and hiking to name a few.
GPS will not meet all users needs. Even with SA turned off, for instance, commercial airlines, ships navigating in harbors and railroads, who all need the most accurate positioning information, will need what is known as Differential GPS (DGPS). This would be offered locally with high-fidelity correction systems. |
