[time-nuts] gLAB PPP noisy clock residuals

[Ole Petter Ronningen]

Hi, all

Not sure if this is 100% within scope of the list, but still: I am trying
to get some good stability measurements of my hydrogen maser, using GPS
L1/L2 and PPP. I collect L1/L2 code and phase observables continously, and
process daily RINEX-files with PPP software and IGS corrections.

I've used the NrCAN-PPP online service, which gives reasonably good
results. The issue with NrCAN is that it only process in the forward
direction (at least, this is what I assume, looking at the results.) So I
want to run the processing locally so that I can run it both forward and
reverse.

I have not been able to get a copy of the nrcan-ppp softwarepackage, so I
am looking elsewhere. ESA gLAB looks like it might fit the bill. The
problem, in short, is that the data I get from  postprocessing with gLAB is
much, _much_ noisier than the results I get from submitting the RINEX files
to NrCAN-PPP online service.

(see attached screenshot - note I've cut away the first 2-3 hours of noisy
data from nrcan)

I've tested this on both a Trimble NetRS and a Novatel OEMV3, and I get
comparable results from both: nice smooth data from NrCAN (except the first
2-3 hours), jagged noisy data from gLAB.

(The Novatel required jumping through MANY hoops before I could get any
usable data, including writing a RINEX-converter. In case someone wants to
play along..)

I'd be tempted to think NrCAN applies smoothing somewhere, but the .sum
file contains "Parameter smoothing: NO"

I am running gLAB with 5-second interval observations, IGS Rapid products
(*.sp3, 10 degree clock interpolation), forward/reverse, throw away the
forward, grab clock offset from the FILTER output, convert to ns - as A.
Wallin is doing in ppp-tools.

So, in summary; does anyone know what is going on? Am I missing some step
in the gLAB processing?

Thanks for any insight.

Ole
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