[time-nuts] What time scale does IGS use to report its clock files?

[Skip Withrow]

Hello time-nuts,
I have been doing some GPS PPP work (mostly with NrCan) and have a question
as to what clock scale the IGS clock products are referenced to?

I would assume that the GPS data is GPS time, which is steered by
UTC(USNO).  So, clock solutions that I compute should be corrected by the
difference between USNO and BIPM to get UTC.

What about other satellite constellations?  I'm sure IGS keeps track of
them as well.  And I'm sure that Galileo, Glonass, and the rest use
different time scales.  Do IGS clk files represent the system that they are
reporting, or is there some translation to a common time scale?

I tried doing some research and did not come up with anything definitive.
Any pointers in the correct direction would be appreciated.

Thanks,
Skip Withrow