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| -rw-r--r-- | www/gps-hacking.html | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/www/gps-hacking.html b/www/gps-hacking.html index c86a2907..9a66e3ac 100644 --- a/www/gps-hacking.html +++ b/www/gps-hacking.html @@ -144,8 +144,11 @@ satellites were programmed to introduce patterned timing jitter into the signals. The U.S. military knew the pattern, but nobody else did (or, at least, nobody who was admitting it).</p> -<p>Now that 'Selective Availability' is gone, the important limits are -natural. One is a variable amount of signal lag produced as the GPS +<p>In Sep 2007 the U.S. government announced that the future generation +of GPS satellites, known as GPS III, will be without the SA feature. +Doing this will make the policy decision of 2000 permanent. +The important limits are on accuracy are now due to physics. +One is a variable amount of signal lag produced as the GPS signals pass through the ionosphere and troposphere, which partly refracts radio waves. This can be largely compensated for by a technique called "Differential GPS" or DGPS. Ground-based reference |