DOD, DOT support GPS signal

Civilian users of the 24 satellite-based highly accurate Global Positioning System won a guarantee of improved accuracy in the future in a joint planning document backed by the Defense and Transportation departments.

The document the biannual "Federal Radionavigation Plan" (FRP) calls for the addition of a second civil frequency to future GPS satellites as well as assurances that civil users can continue to access the noncoded portion of the military GPS frequency until that second signal becomes operational.

GPS receivers perform space-age triangulation with the satellites to derive highly accurate positioning and navigation with the civil signal delivering 100 meters or better accuracy and the military signal delivering 20 meters or better. DOD developed GPS as a means for providing highly precise inputs to weapon systems as well as a navigation system for aircraft vessels ground troops and vehicles.

The availability of the civil signal has led to the development of a multibillion-dollar GPS industry that has become an essential tool for users ranging from surveyors to backpackers. The Federal Aviation Administration plans to transition most of its air traffic control systems to GPS in the next century (see WAAS story Page 3) and this growing civil community wants improved accuracy from the GPS system which the second signal would provide.

The release of the 1996 version of the FRP was delayed pending resolution of the second civil signal issue.

William Strange project chief for the GPS-based Continuously Operating Reference Station (CORS) system operated by the National Geodetic Survey (NGS) welcomed the language in the new FRP guaranteeing civil access to the military signal.

"If we did not have access to the carrier phase signal it would not be possible to do the precise surveying necessary to monitor crustal plates " Strange said. Accessing both GPS signals from a multiple-receiver network CORS can deliver accuracies measured in the millimeter or centimeter range - enough to detect the motion in the earth's crustal plates helping NGS to monitor earthquake faults.


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