Posted by Chuck Tribolet on March 24, 2003 at 16:14:16:
In Reply to: Switched to DGPS shortly before ... posted by Bob3 on March 20, 2003 at 07:43:48:
Back when was SA on, it was more than a 20' difference.
The accuracy with SA off, no differential or WAAS,
is about 15 meters or better, 95% of the time.
With SA on, no differential or WAAS, it was 100
meters or better, 95% of time, and could vary
from 100 meters thataway to 100 meters the other
way in a couple of minutes. I remember sitting on
Outer Pinnacles in Carmel Bay and, watching my
position vary from somewhere on Inner Pinnacles to
way over the in the middle of the bay in a couple
of minutes. You could get calculated velocies of
20 knots or beter. At anchor.
But the localized jamming/spoofing the US military
is generally accepted to have makes SA unnecessary. And all modern (last couple of years)
GPS receivers have WAAS (Wide Area Augmentation
System, satelite delivered DGPS), which improves
the accuracy to 3m, 95% of the time, even if SA
is on.
Chuck