Tuesday, June 01, 2010

End of Selective Availability Anniversary

The June 2010 issue of  Forestry Source (subscription required) contains a short primer on GPS. Author Steve Wilent mentioned the tenth anniversary of the end of Selective Availability (SA) on May 1, 2000, following an executive order by President Clinton. Under the SA program deliberate error was introduced into the GPS signal so that the live signal would have an error of about 100 meters. This was done to protect national security during military operations. Only military GPS receivers had a chip to remove the error.

The policy was changed to promote the use of GPS in the general economy. The military agreed fully with the new policy. There were ways around SA, by using a supplemental FM correction signal broadcast locally by the US Coast Guard or by doing post-processing correction of field data in the office.

Now that the GPS signals has no more deliberately introduced error the use of GPS has grown dramatically  in all parts of the economy from cars to personal devices. The sport of geocaching would not be possible if SA were still in operation.

For foresters, the end of SA has meant that low cost, rugged, recreational grade GPS receivers can be used for most forestry operations. The accuracy of these receivers is more than enough for most forestry mapping  operations. The forest technology program at Penn State Mont Alto has been able to acquire sufficient receivers so that all the students can have one to use for field work. Collecting GPS data in the field and using it to create maps has now become a normal part of all fieldwork.

We should make the end of SA a national holiday!

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