AuntieNae's Coin Club 05 Sept Geocoin

My goal is to be part of AuntieNae’s Geocoin collection. I will be shared at events or if you meet AuntieNae on the trail.

Please do not drop into or out of caches. Simply use the "Discovered" log feature. Thanks!

This is AuntieNae's 1st Coin Club Coin. It is actually the second month edition, issued in September 2005.

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).

President Bill Clinton, May 1, 2000 in a press release.

This is a day that will live in the hearts of Geocachers. It's almost as big as the date of the first Geocache stash hide. Yet, May 1, 2000 was a day that I'll never remember what I was doing and this simple press release didn't impact many of our lives until two, three, or even five years later. Such a huge act and yet so little fanfare.

The reason that this barely hit our radars in 2000 is simple. The whole topic is way too complex to be a news story longer than "In other news, Selective availability of GPS signals has been set to zero, making it possible for GPS units to have better accuracy." Any more detail would probably require more time than anyone would be willing to listen to at that time. Now that we use GPS signals with a SA setting of 0 on a daily basis, we are more tuned in to the mechanics of this technology.

Selective Availability is technology built into the US GPS transmissions which obscures the true distance between the receiver and the GPS satellite. Imagine that you are taking measurements for a fence and the wind is blowing your measuring tape strongly. At any given point in time, your measurement will vary. Compared to the true distance, your measurement may be a foot too long when a heavy gust blows by or sometimes you will be pulling against the wind as it stops and pull it away from the other end, resulting in a measurement that is too short. Using the "Measure 300 times; Cut once" rule, your average should be close to the true distance but will not be exactly the same.

Selective Availability applies this same kind of error to the calculations that a GPS makes from the GPS signals. The result is that in order for a GPS to achieve a precise location, it would need to average thousands and thousands of transmissions from each GPS satellite until it could narrow down a moderately precise location. In April of 2000, this produced an accuracy of 100 meters. A GPS receiver's calculation could actually be closer to the target but the error allowance was 100 meters. Special use GPS units could be set out for a longer time with a high powered antenna to determine a more precise location for applications such as construction and surveying. For what we currently think of as consumer uses of GPS, this was not helpful.

By eliminating the error caused by SA, the United States government opened up a whole new world in the travel, shipping, and adventure sport industries worldwide. This also enabled the ability to place a cache in the woods and list it for people to find on a newsgroup or web site.