Re: GPS + Pulsars + an apology/rebuttal

> > What I don't understand is how they are claiming accuracy within
inches
> when GPS is within a meter.

There are three grades of GPS unit  -  civilian, commercial and military
-
accuracy does vary depending on the category - and will vary within the
category depending on the quality and the age of the unit in question.
Civilian units will give you a potential accuracy of 1 metre with an
average
accuracy of 5 metres - Commercial airlines use better units with a
greater
level of refinement that was more important when the dither factor was
still
active - Military units can give potential accuracy of centimetres with
an
average accuracy depending on the number of satellites "overhead" of
about
30-50 centimetres. I have worked with all three types and found that
military units were great but generally unavailable to the public and
commercial models can cost more than military units....

> I believe they're using ground stations which have a beacon. That
helps to
> reduce the error down to very small amounts.

Differential beacons are in use in many countries but have limited range
-
usually 250-300 km - (not much use in the middle of a desert or the
ocean)
and are generally confined to major cities and heavy air routes - the
expansion of the DGPS network in most countries has stalled due to the
dropping of the dither factor for civilian use.

Brendan