Here are some fun facts about the GPS Satellite Constellation (the GPS system we use).
The Air Force manages the constellation to ensure the availability of at least 24 GPS satellites, 95% of the time. For the past several years, the Air Force has been flying 31 operational GPS satellites, plus 3-5 decommissioned satellites ("residuals") that can be reactivated if needed.
- The United States government currently claims 4 meter accuracy for civilian GPS. Mind you, that's the minimum. Some devices/locations reliably can get 3 meter accuracy. 4 meters is about 12 feet - so the best you can get is about a 24 foot diameter circle.
- The first GPS satellite was launched in 1978.
- A full constellation of 24 satellites was achieved in 1994.
- Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
- A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
- Transmitter power is only 50 Watts or less.
Most geocachers have run into either a geocache whose coordinates are less than desirable. The worst coordinates for a geocache I ever attempted to find were more than 2 miles off. Oh, and we got FTF (via a hint from the CO).
All sorts of things can throw off coordinates including clouds, weather, trees, buildings, and sometimes just the minerals in or on the ground at the ground zero. We have a LARGE geocache hidden in a giant stack of granite blocks. We get plenty of DNF logs! Good luck getting a decent lock there - plenty of bounce.
Another factor in accuracy is time. Here is an example of GPS accuracy from a handheld GPS (Garmin Oregon). The first image was taken 1 minute after the GPS was switched on , the middle image is after 2 minute and the last image is after 3 minutes. You can see on the GPS screen that more satellites are being received as time goes on (the green bars) and the Location coordinates are slowly changing as the accuracy begins to come down to the final . The final Location coordinates are N51°35.203' W4°19.501' which can be considered quite accurate.
So, knowing all this - how do we get more accurate coordinates for a cache.
Stay Safe & Keep Caching!!!