GPS velocity accuracy
I've been doing a bit of work on the use of GPS for calibrating airspeed measurement systems (yes, I know the theory and the maths !).
The one thing that I've been struggling with is finding any rigorous estimate of the accuracy of velocity measurement using GPS - all the available references spend a lot of time considering 2D positional accuracy, a bit less worrying about geopotential altitude accuracy, but then pretty much ignore velocity. I've come across the catalogue for a company who sell GPS based units for measuring race-car performance who quote ±0.1kph, but I suspect that this is most likely a bit of inspired guesswork.
So, can anybody point me at a reference document or paper anywhere that does a rigorous job of estimating the errors in velocity (groundspeed) measurement with GPS?
G