[time-nuts] GPS/UTC time

[Jim Lux]

On 7/4/15 2:01 PM, Tom Van Baak wrote:
>> (the Japan earthquake in 2011 sped the earth up by 1.8
>> microseconds/day. The Sumatra quake on 26 Dec 2004 had a bigger
>> effect: 6.8 microseconds)
>
> Hi Jim,
>
> Just in case you didn't know -- these are theoretical results only.
> There's a guy at JPL (Richard Gross) who does the calculations and
> any time there's a big seismic event he runs the simulations and out
> comes a number. That's pretty cool but the numbers so far are always
> smaller that what VLBI can actually measure. Still, it makes a nice
> press release and physics lesson.

Yes, that's true.

I wonder, though, if over time, they can measure it: they're collecting 
a lot of GPS data from around the world, and the GPS constellation is 
reasonably fixed in inertial space.

Although, if the earth rotation changes, and earth's mass distribution 
isn't perfectly symmetric, then that will change the orbits of the 
satellites.

I could envision that they are building a very complex model of GPS 
orbits and earth underneath it, and they could somehow see the transient 
in the model parameters.  (as the papers you cited show)


The measurements are always getting better.  There's also VLBI of 
stellar sources, and that's getting better too, as they model out all 
the perturbations.


One can hope..<grin>