BBC News Online: Sci/Tech

Satellite navigation accuracy boosted

GPS is a free service used by over four million people worldwide, but until 0000 GMT on Monday night the signal was deliberately degraded by the US military.

The move will allow users such as sailors, motorists and hikers to pin down their position to at least 20 metres and perhaps 10m. The previous best was 100m.

Military gain

However, John Pike, a space policy analyst at the Federation of American Scientists think tank, believes the action was not entirely altruistic.

He said the US would benefit from the continued global use of its system, meaning the US military retains control of the technology. Offering the better US system for free takes away some of the incentive for another country or consortium to build a competing system, he added.

Announcing the GPS upgrade, US President Bill Clinton said: "The decision to discontinue [signal degradation] is supported by threat assessments which conclude it would have minimal impact on national security."

Restricted access

GPS was originally developed by the US Department of Defense and the military have developed even more accurate systems than are now available. They have also reserved the ability to degrade the signal in particular regions of the world, if military objectives make that desirable.

It took four years of deliberation to decide to increase the precision of GPS but it will be a major boost to the GPS industry. This is already expected to double in the next three years from $8bn to more than $16bn.