[teqc] helpful tip of week 1918

Lou Estey lou at unavco.org
Fri Oct 14 12:43:58 MDT 2016


This week's tip: the mp12 qc change done in Oct 2013

This week a teqc user at National Observatory of Athens (NOA), Greece, reported
something that at first seemed quite odd: For GPS-only data (i.e. no unusual new
GNSS influence) at a site, teqc was reporting a slightly lower value for the mp12
multipath RMS using a teqc version 2013Mar15:

Moving average MP1      : 0.879445 m

vs. that from version 2016Apr1:

Moving average MP12     : 0.933821 m

The same result occurs over most days for this site spanning 8 years of data.
However, the mp21 multipath RMS is essentially the same for this period for all
days.  What was the reason?

It turns out to be due to the change in one constant in the qc made for mp12 in
Oct 2013 when I was overhauling the qc code to deal more generally with GNSS data.
In particular, there is a seed value for each multipath rms, written out in teqc's
report file, which shows the change:

diff *.13S*
1c1
< version: teqc  2013Mar15
---
 > version: teqc  2016Apr1
[...]
76c77
< IOD or MP slips         :    412
---
 > IOD or MP slips         :    399
[...]
87,89c88,90
< Expected rms of MP1 multipath      : 50.00 cm
< Expected rms of MP2 multipath      : 65.00 cm
< Multipath slip sigma threshold     : 4.00 cm
---
 > Expected rms of MP12 multipath     : 65.00 cm
 > Expected rms of MP21 multipath     : 65.00 cm
 > Multipath slip sigma threshold     : 4.00 sigma
[...]

In October 2013, this seed value called the "expected rms" of mp12 was increased from
50 cm to 65 cm, basically to bring it into alignment with the other mp1* seed values.
My tests here showed essentially no change.  Plus, UNAVCO's software monitors qc changes
at sites like those in the 1100 sites of the Plate Boundary Observatory in the western
US and Alaska and nothing was were noted when we switched to post-Oct 2013 versions of
teqc to do the qc on sites.

But, apparently, for some sites, changing these seed values in the range of 50-70 cm
expected RMS makes a noticeable change.

You'll also note that after increasing this seed value for mp12 RMS, that the multipath
slip count decreased.  This is to be expected; there's a rough inverse relationship.
Increase the expected RMS, decrease detected slips; decrease the expected RMS, increase
detected slips -- generally speaking.

If you see this change in mp12 RMS, is there anything you can do?  Yes: change the seed
value back to the original 50 cm (pre-Oct 2013 value) with this option:

[662] teqc +help | grep _rms | grep mp12
                 -mp12_rms[cm] #          set expected mp12 rms to # cm (default = 65.00)

i.e. use '-mp12_rms 50'.  That's all that's needed.  (Now, having said that, I should
point out that you should not get too excited about any sub-cm precision in the multipath
RMS values from teqc.)

In fact, there is a whole bunch of these for different GNSS multipath combinations that
can be adjusted from the current defaults:

[669] teqc +help | grep _rms
                 -mp12_rms[cm] #          set expected mp12 rms to # cm (default = 65.00)
                 -mp21_rms[cm] #          set expected mp21 rms to # cm (default = 65.00)
                 -mp15_rms[cm] #          set expected mp15 rms to # cm (default = 65.00)
                 -mp51_rms[cm] #          set expected mp51 rms to # cm (default = 65.00)
                 -mp16_rms[cm] #          set expected mp16 rms to # cm (default = 80.00)
                 -mp61_rms[cm] #          set expected mp61 rms to # cm (default = 80.00)
                 -mp17_rms[cm] #          set expected mp17 rms to # cm (default = 90.00)
                 -mp71_rms[cm] #          set expected mp71 rms to # cm (default = 90.00)
                 -mp18_rms[cm] #          set expected mp18 rms to # cm (default = 100.00)
                 -mp81_rms[cm] #          set expected mp81 rms to # cm (default = 100.00)

Quite honestly, I had been hoping that someone would take up the challenge of finding
optimal values for all these multipath combinations for the various GNSS constellations.
This week, I also briefly discussed this topic with Freddy Blume, head of UNAVCO's D&T group,
and this may be a item that the group could devote some resources to study.

Happy teqc-ing!

cheers,
--lou

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Louis H. Estey, Ph.D.              office:  [+001] 303-381-7456
UNAVCO, 6350 Nautilus Drive           FAX:  [+001] 303-381-7451
Boulder, CO  80301-5554            e-mail:  lou  unavco.org
      WWW:  http://www.unavco.org   http://jules.unavco.org

"If the universe is the answer, what is the question?"
                                                -- Leon Lederman
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Past helpful tips:

week 1894: using teqc config files - http://postal.unavco.org/pipermail/teqc/2016/002067.html
week 1895: qc of high-rate data - http://postal.unavco.org/pipermail/teqc/2016/002071.html
week 1896: UNIX/Linux shells for Windows - http://postal.unavco.org/pipermail/teqc/2016/002072.html
week 1897: '-' vs. '+' teqc options - http://postal.unavco.org/pipermail/teqc/2016/002076.html
week 1898: auto-identification of formats - http://postal.unavco.org/pipermail/teqc/2016/002092.html
week 1899: auto-identification vs. format flags - http://postal.unavco.org/pipermail/teqc/2016/002096.html
week 1900: square brackets in options - http://postal.unavco.org/pipermail/teqc/2016/002105.html
week 1901: using option '+mds' - http://postal.unavco.org/pipermail/teqc/2016/002108.html
week 1902: qc results w/ problematic nav messages - http://postal.unavco.org/pipermail/teqc/2016/002113.html
week 1903: '-no_orb[it]' and '-no_pos[ition]' options - http://postal.unavco.org/pipermail/teqc/2016/002115.html
week 1904: '-week' option - http://postal.unavco.org/pipermail/teqc/2016/002117.html
week 1905: using '+bcf' for XYZ/geodetic conversion - http://postal.unavco.org/pipermail/teqc/2016/002126.html
week 1906: the '+v[erify]' option - http://postal.unavco.org/pipermail/teqc/2016/002128.html
week 1907: '+C2', '+L5', "+L6', '+L7', '+L8', and '+all' options - http://postal.unavco.org/pipermail/teqc/2016/002130.html
week 1908: no doppler shortcut; RINEX L2 - http://postal.unavco.org/pipermail/teqc/2016/002131.html
week 1909: using paths w/ file names - http://postal.unavco.org/pipermail/teqc/2016/002132.html
week 1910: the (un)importance of file names - http://postal.unavco.org/pipermail/teqc/2016/002133.html
week 1911: notices, warnings, and errors - http://postal.unavco.org/pipermail/teqc/2016/002134.html
week 1912: the '-max_rx_SVs' option - http://postal.unavco.org/pipermail/teqc/2016/002137.html
week 1913: the end of '++igs' and '+igs' - http://postal.unavco.org/pipermail/teqc/2016/002140.html
week 1914: splicing together RINEX files - http://postal.unavco.org/pipermail/teqc/2016/002144.html
week 1915: using '-O.int' and '-O.dec' - http://postal.unavco.org/pipermail/teqc/2016/002145.html
week 1916: '+doy' option - http://postal.unavco.org/pipermail/teqc/2016/002146.html
week 1917: '-tbin' and '-ast' options - http://postal.unavco.org/pipermail/teqc/2016/002152.html




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