Recalibration after axis tilt?

I read today that the earthquake off Japan resulted in a shift in the Earth's
axis of about four inches, and moved Japan's coast by a couple of meters. How
is GPS calibrated to take this into account? It seems to me that the axis
shift could be significant for very high-precision measurements, and the
movement of the coast would require reworking a great deal of map data as
well.

Mxsmanic wrote:

Who has maps readable or accurate to a couple of metres?

Mike.
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On 2011.03.12 15:04 , Mike Coon wrote:

Moved the entire island of Honshu by a couple meters is what I've read.


It isn't. GPS doesn't care about where things actually are - only the
satellite's longitude of ascending node is of importance (relationship
to prime meridian) and the actual pole alignment of the earth.

Maps are another matter.

The other thing that affects GPS is the speeding up of the earth's
rotation immediately after the earthquake (subduction mass results in a
conservation of momentum increase in the earth's spin rate - I think it
was on the order of about 1.6 microseconds (shorter day).

And then there is the tilting of the earth's axis as well (due to the
earthquake).


Many mapping agencies have control points accurate to the mm level - at
least between points in a local system.

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Alan Browne writes:


Well, if the axis of rotation moved, that would the pole alignment of the
Earth, right? So how is the system updated to account for the change? The
Earth has moved slightly, but the orbits of the satellites presumably have not
(although I suppose they might be slightly perturbed as well to the extent
that the planet's mass is not symmetrical about its center).


I had not thought of that. So how is that accounted for?

Are ground stations measuring the positions of satellites and updating them,
or what? How long does the process take?

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I think, but I'm not sure, that the inclination of the orbits in the
ephemeris has been slighly changed.

I tried to plot the inclination of all the SV in the constellation for
the 3 days before and after the JApan earthquake, but you can see any
evident change on 11 march.
The inclination changes over time, but no anomaly found on 11 march.
Maybe that the change is lower than the normal change between

Note: I used only the inclination for the plot.


GPS time goes for itself, no changes are done, I think. It goes on
without taking in account the earth rotation.
Maybe it will affet the leap seconds count (the difference between
UTC and GPS time may have changed, if UTC take into account this
1.6us)

em,

Sure groud stations monitor the satellites. I think that the
information on each satellite can be update once per day (but you can
upload several days of data)