[time-nuts] Re: ADEV on data with gaps

[Lux, Jim]

On 8/4/23 9:15 AM, Lux, Jim via time-nuts wrote:
> I've got a series of clock measurements where the actual measurement 
> occasionally has problems (e.g. it's measured against GPS, and there 
> are GPS partial outages).
>
> What's a strategy for calculating ADEV (and related parameters) where 
> there are data in the sequence that are excised? For example, does 
> Timelab or Stable32 have a way to have timestamps for the 
> frequency/phase measurements that recognizes gaps?
>
> At a first glance, it seems that the calculation for each tau will 
> have a different number of measurements contributing.  Say I have 1000 
> seconds of data, once a second, and there's a gap of 100 seconds 
> somewhere in the middle.  For the 1 second tau, I've got 900 
> measurements.  for a 100 second tau, I'll have 800 measurements 
> (because for 200, one or the other end point is missing), etc.
>
> Some plots attached showing some data.  In this case, I'm looking at a 
> post calculated "clock bias" between GPS and the clock - that is, 
> there's a process that estimates the clock offset (in meters). A first 
> difference gets rate, and clock has some relatively fixed bias (that 
> changes with time), and random variations on top of that.  However, 
> the measurement depends on the SNR of the GPS signals (lower plot on 
> biasdrift, it's the measurement uncertainty estimate)
>
> At some point, of course, the ADEV measurement is limited by the GPS 
> measurement uncertainty - if it's 1 ns, then ADEV is never going to 
> measure less than 1E-9 over 1 second. 



Digging into Stable32 (or more specifically 
http://www.wriley.com/Gaps.htm) it appears that it's doable. Now I just 
have to try generating a data file with the right format to ingest.