If you are using a GPS with WAAS, LAAS, or differential augmentation the GPS
corrects itself in "real time" through constant reffrence to known "ground
truth" transmitters.
"Brian Whatcott" wrote in message
...
On Wed, 29 Dec 2004 03:28:18 GMT, Geoff Schultz
wrote:

I was watching the NBC nightly news tonight and they stated that the
rotation of the Earth was effected by the tsunami. According to the
report
the day of the tsunami was slightly shorter than standard day, which would
mean that the roation increased slightly. They didn't state if the
rotational change was permanent of a 1 time event.

I was wondering if this induced an error in GPS positioning as the Earth
isn't where it is expected to be. In my way of thinking we shifted
slightly easterly. I have no idea how much of a change this is, or even
if
it's measurable withn the error of a GPS, but it's an interesting
question.

-- Geoff

I looked over the World data archive for Earth rotation, it comprises
VLBI and GPS measurements from dozens of stations world wide.
And I checked with the Oklahoma Seismic record.

This is what I found. Oklahoma registered a force 9 seismic event on
Dec 26th which gave a slow vibration in these parts of just under 1/8
inch amplitude, period 20 seconds [if I recall]. This was likely
experienced in most parts of the World.

The day length varies EVERY day, in a cyclic manner - there's a 29 day
component and a 12 day component etc., and on the graph I plotted at
least, it looked as though Dec 26th was a little shorter than the
cycle would have predicted - a fraction of a millisecond maybe - on a
variation that goes uip and down by 3 4 or 5 milliseconds per day at
times.

Atmospheric pressure, winds, sea currents, major storms, core
events, and big seismic events are known to vary the day length
in this way.

GPS ground stations at known co-ordinates are monitored in order to
adjust satellite emissions to maintain those co-ordinates.

Brian Whatcott Altus OK