GPS accuracy

Thomas Yancey yancey at GEO.TAMU.EDU
Mon May 1 16:27:08 CDT 2000

The following message was sent around offices of the National Science
Foundation today. It portends major benefits for anyone using GPS.

> >
> > THE WHITE HOUSE Office of the Press Secretary
> > For Immediate Release: May 1, 2000
> >
> > Today, I am pleased to announce that the United States will stop the
> > intentional degradation of the Global Positioning System (GPS) signals
> > available to the public beginning at midnight tonight.  We call this
> > degradation feature Selective Availability (SA).  This will mean that
> > civilian users of GPS will be able to pinpoint locations up to ten times
> > more accurately than they do now.  GPS is a dual-use, satellite-based
> > system that provides accurate location and timing data to users worldwide.
> >
> > My March 1996 Presidential Decision Directive included in the goals for
> > GPS to: encourage acceptance and integration of GPS into peaceful civil,
> > commercial and scientific applications worldwide; and to encourage private
> > sector investment in and use of U.S. GPS technologies and services.  To
> > meet these goals, I committed the U.S. to discontinuing the use of SA by
> > 2006 with an annual assessment of its continued use beginning this year.
> >
> > The decision to discontinue SA is the latest measure in an on-going effort
> > to make GPS more responsive to civil and commercial users worldwide.
> > Last year, Vice President Gore announced our plans to modernize GPS by
> > adding two new civilian signals to enhance the civil and commercial
> > service.  This initiative is on-track and the budget further advances
> > modernization by incorporating some of the new features on up to 18
> > additional satellites that are already awaiting launch or are in
> > production.  We will continue to provide all of these capabilities to
> > worldwide users free of charge.
> >
> > My decision to discontinue SA was based upon a recommendation by the
> > Secretary of Defense in coordination with the Departments of State,
> > Transportation, Commerce, the Director of Central Intelligence, and other
> > Executive Branch Departments and Agencies.  They realized that worldwide
> > transportation safety, scientific, and commercial interests could best be
> > served by discontinuation of SA.  Along with our commitment to enhance GPS
> > for peaceful applications, my administration is committed to preserving
> > fully the military utility of GPS. The decision to discontinue SA is
> > coupled with our continuing efforts to upgrade the military utility of our
> > systems that use GPS, and is supported by threat assessments which
> > conclude that setting SA to zero at this time would have minimal impact on
> > national security.  Additionally, we have demonstrated the capability to
> > selectively deny GPS signals on a regional basis when our national
> > security is threatened.  This regional approach to denying navigation
> > services is consistent with the 1996 plan to discontinue the degradation
> > of civil and commercial GPS service globally through the SA technique.
> >
> > Originally developed by the Department of Defense as a military system,
> > GPS has become a global utility.  It benefits users around the world in
> > many different applications, including air, road, marine, and rail
> > navigation, telecommunications, emergency response, oil exploration,
> > mining, and many more.  Civilian users will realize a dramatic improvement
> > in GPS accuracy with the discontinuation of SA.  For example, emergency
> > teams responding to a cry for help can now determine what side of the
> > highway they must respond to, thereby saving precious minutes.  This
> > increase in accuracy will allow new GPS applications to emerge and
> > continue to enhance the lives of people around the world.

Thomas E. Yancey
Dept. Geology & Geophysics, Texas A&M University
College Station, Texas 77843-3115
ph: 979-845-0643
tyancey at

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