[teqc] helpful tip of week 2017

Lou Estey lou at unavco.org
Wed Sep 5 08:16:04 MDT 2018


This week's tip: qc: multipath rms

The qc of multipath rms values 'mp1' (= mp12) or 'mp2' (= mp21) just before the
'o/slps' at the end of the SUM line, e.g.

       first epoch    last epoch    hrs   dt  #expt  #have   %   mp1   mp2 o/slps
SUM 18  8 23 15:01 18  8 23 15:59 .9819   1  63116  59314  94  0.07  0.08  11863

like the observations per slip value in last week's tip, are also from the original
qc algorithms, also developed by others at UNAVCO in the early and mid 1990's for
GPS-only data.  Back in those days the only multipath pseudorange-and-phase combinations
that could be made were from the observables from the GPS signals on the L1 and L2
carrier frequencies.  Later in teqc, I added the multipath combinations from the
GLONASS signals on the G1 and G2 carrier frequencies, but included these in with
the GPS mp1 and mp2 due the proximity of GLONASS G1 and G2 frequencies to the GPS
L1 and L2 frequencies.

With the arrival of GPS and SBAS L5 and other new constellations with their
signals, it was time to expand the original nomenclature, so that now:

mpMN rms uses a combination of pseudorange and phase from signal M with phase from signal N

(This nomenclature overhaul in teqc was introduced back in Oct 2013 when I finally had
to deal with Beidou data; see https://postal.unavco.org/pipermail/teqc/2013/001619.html
and again in tip of the week https://postal.unavco.org/pipermail/teqc/2017/002302.html.)
Since we're almost 5 years into this multipath nomenclature change, hopefully it's
perfectly logical by now.)

There are many combinations possible, but in order to keep the zoo to a minimum size,
in teqc's current design one of the frequencies is always the principle frequency of
the system, i.e.:

GPS, SBAS, and QZSS L1
GLONASS G1
Galileo E2-L1-E1
Beidou B1/E2

... or (extended) RINEX 2.11's signal '1' for any of the above, e.g. see tables in
https://postal.unavco.org/pipermail/teqc/2017/002302.html or in
https://postal.unavco.org/pipermail/teqc/2018/002475.html.

The multipath rms values are given in qc report and would look like this:

Moving average MP12     : 0.249255 m
Moving average MP21     : 0.237741 m
Moving average MP15     : 0.236902 m
Moving average MP51     : 0.251431 m
Moving average MP17     : 0.406232 m
Moving average MP71     : 0.401194 m
Moving average MP18     : 0.444590 m
Moving average MP81     : 0.388970 m

with the mp12 and mp21 rms values repeated (and reported to a more sensible centimeter
precision) in the qc SUM line.

In order to keep the original qc SUM line the same for compatibility, a new summary
line, SMP, was introduced to show the original mp12 and mp21 plus any other new combinations.
Below are the results for four different modern receivers that we happen to be testing
right now, all simultaneously using signals from a single GNSS antenna (via a splitter)
here at Boulder, Colorado:

Receiver 1:
       first epoch    last epoch    mp12  mp21  mp15  mp51  mp17  mp71  mp18  mp81
SMP 18  8 25 00:00 18  8 25 23:59  0.25  0.24  0.24  0.25  0.41  0.40  0.44  0.39
       first epoch    last epoch    hrs   dt  #expt  #have   %   mp1   mp2 o/slps
SUM 18  8 25 00:00 18  8 25 23:59 24.00  15 136145 133085  98  0.25  0.24   4159

Receiver 2:
       first epoch    last epoch    mp12  mp21  mp15  mp51  mp16  mp61  mp17  mp71  mp18  mp81
SMP 18  8 25 00:00 18  8 25 23:59  0.35  0.27  0.35  0.26  0.29  0.25  0.46  0.44  0.47  0.39
       first epoch    last epoch    hrs   dt  #expt  #have   %   mp1   mp2 o/slps
SUM 18  8 25 00:00 18  8 25 23:59 24.00  15 135511 132292  98  0.35  0.27    175

Receiver 3:
       first epoch    last epoch    mp12  mp21  mp15  mp51  mp17  mp71  mp18  mp81
SMP 18  8 25 00:00 18  8 25 23:59  0.43  0.38  0.44  0.27  0.51  0.46  0.50  0.40
       first epoch    last epoch    hrs   dt  #expt  #have   %   mp1   mp2 o/slps
SUM 18  8 25 00:00 18  8 25 23:59 24.00  15 134431 129240  96  0.43  0.38  11749

Receiver 4:
       first epoch    last epoch    mp12  mp21  mp15  mp51  mp16  mp61  mp17  mp71  mp18  mp81
SMP 18  8 25 00:00 18  8 25 23:59  0.32  0.26  0.53  0.23  0.27  0.24  0.46  0.43  0.46  0.40
       first epoch    last epoch    hrs   dt  #expt  #have   %   mp1   mp2 o/slps
SUM 18  8 25 00:00 18  8 25 23:59 24.00  15 136145 133313  98  0.32  0.26   6348

All four are using 15-second sampling, all four are tracking GPS+GLONASS+SBAS+Galileo+Beidou
(and one rx tracked at few epochs of QZSS J02, visible above 10 degrees for a wee while
even here in the middle of North America), all four were tracking all signals that they
were capable of tracking, and, to our knowledge, there is no firmware multipath mitigation
turned on.  (A second day of tracking shows essentially the same results, so these results
are not a fluke of this one day.)

Note that receivers 2 and 4 are showing mp16 and mp61 multipath rms.  This is because
those units are capable of tracking Galileo E6, so those two multipath combinations can
be obtained when Galileo E6 observables are combined with the primary Galileo E2-L1-E1
observables, as explained above.

(For those of you who paid attention to last week's tip of the week on the observations
per slip value, you'll note that there's a pretty wide range of values.  But I'd say that
all of the data collected here, on all four receivers, is perfectly acceptable.)

You'll note that the multipath rms combinations don't necessarily agree between
receivers and, in fact, there's a range of +/-30-ish% for our old familiar
mp12 and mp21 combinations (which are from GPS and GLONASS, and a wee bit of QZSS
on one of them) -- but the values of the different receivers for the same combination
are not wildly different.  They are hardly the same, either.

Personally, I'm of the opinion that, like the observations per slip value, one shouldn't
get too religious about interpreting multipath rms values as "good" or "bad".

Like the observations per slip value, I'm of the opinion that the major utility of the
multipath rms values for a permanent station is to track the values during the lifetime
of the site and look for significant changes.  If you introduce a new antenna, or
new receiver, or new receiver firmware, or a change in the radome, or change the
receiver configuration in some way (e.g. change which constellations and/or signals
are being tracked), then note any change in multipath rms.  But don't get too excited
unless you understand what the reasons for the rms changes might be.  But, if there's
been no equipment or firmware or configuration changes, and you see a consistent change
in multipath rms over time, this is probably a good argument to look for a root cause,
which might be:

- the introduction of man-made object(s) or equipment near the site, esp. when metal
   in involved, giving rise to a fairly rapid increase multipath rms
- natural growth around the site, giving rise to a slow decrease in multipath rms
- a pinched antenna cable, giving rise to an increase in multipath rms, which might
   be slow or fast, depending on how the pinch is caused
- (rare, but possible) degraded receiver tracking (one or more aging components?),
   giving rise to an increase in multipath rms

or for the first two cases there would be the reverse effect if removing man-made
objects or natural growth.

To the first order, anyway, that's what a few of us here at UNAVCO came up with.

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

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

Past helpful tips:

week 1894: using teqc config files - https://postal.unavco.org/pipermail/teqc/2016/002067.html
week 1895: qc of high-rate data - https://postal.unavco.org/pipermail/teqc/2016/002071.html
week 1896: UNIX/Linux shells for Windows - https://postal.unavco.org/pipermail/teqc/2016/002072.html
week 1897: '-' vs. '+' teqc options - https://postal.unavco.org/pipermail/teqc/2016/002076.html
week 1898: auto-identification of formats - https://postal.unavco.org/pipermail/teqc/2016/002092.html
week 1899: auto-identification vs. format flags - https://postal.unavco.org/pipermail/teqc/2016/002096.html
week 1900: square brackets in options - https://postal.unavco.org/pipermail/teqc/2016/002105.html
week 1901: using option '+mds' - https://postal.unavco.org/pipermail/teqc/2016/002108.html
week 1902: qc results w/ problematic nav messages - https://postal.unavco.org/pipermail/teqc/2016/002113.html
week 1903: '-no_orb[it]' and '-no_pos[ition]' options - https://postal.unavco.org/pipermail/teqc/2016/002115.html
week 1904: '-week' option - https://postal.unavco.org/pipermail/teqc/2016/002117.html
week 1905: using '+bcf' for XYZ/geodetic conversion - https://postal.unavco.org/pipermail/teqc/2016/002126.html
week 1906: the '+v[erify]' option - https://postal.unavco.org/pipermail/teqc/2016/002128.html
week 1907: '+C2', '+L5', "+L6', '+L7', '+L8', '+all' options - https://postal.unavco.org/pipermail/teqc/2016/002130.html
week 1908: getting RINEX doppler and L2 - https://postal.unavco.org/pipermail/teqc/2016/002131.html
week 1909: using paths w/ file names - https://postal.unavco.org/pipermail/teqc/2016/002132.html
week 1910: the (un)importance of file names - https://postal.unavco.org/pipermail/teqc/2016/002133.html
week 1911: notices, warnings, and errors - https://postal.unavco.org/pipermail/teqc/2016/002134.html
week 1912: the '-max_rx_SVs' option - https://postal.unavco.org/pipermail/teqc/2016/002137.html
week 1913: the end of '++igs' and '+igs' - https://postal.unavco.org/pipermail/teqc/2016/002140.html
week 1914: splicing together RINEX files - https://postal.unavco.org/pipermail/teqc/2016/002144.html
week 1915: using '-O.int' and '-O.dec' - https://postal.unavco.org/pipermail/teqc/2016/002145.html
week 1916: '+doy' option - https://postal.unavco.org/pipermail/teqc/2016/002146.html
week 1917: '-tbin' and '-ast' options - https://postal.unavco.org/pipermail/teqc/2016/002152.html
week 1918: mp12 RMS before/after Oct 2013 - https://postal.unavco.org/pipermail/teqc/2016/002158.html
week 1919: the global windowing options - https://postal.unavco.org/pipermail/teqc/2016/002159.html
week 1920: '-M.dec' and '-N.dec' options - https://postal.unavco.org/pipermail/teqc/2016/002163.html
week 1921: combining time filtering options - https://postal.unavco.org/pipermail/teqc/2016/002176.html
week 1922: helping me (or someone else on the list) help you - https://postal.unavco.org/pipermail/teqc/2016/002187.html
week 1923: the "build" line - https://postal.unavco.org/pipermail/teqc/2016/002190.html
week 1924: the qc '-w[idth]' option - https://postal.unavco.org/pipermail/teqc/2016/002193.html
week 1925: qc with explicit time windowing - https://postal.unavco.org/pipermail/teqc/2016/002194.html
week 1926: the '+rx_state' option - https://postal.unavco.org/pipermail/teqc/2016/002200.html
week 1927: the '-O.sum' option - https://postal.unavco.org/pipermail/teqc/2016/002204.html
week 1928: the '+meta' and '+mds' options - https://postal.unavco.org/pipermail/teqc/2016/002206.html
week 1930: more on '-O.sum' - https://postal.unavco.org/pipermail/teqc/2017/002207.html
week 1931: the '-O.s[ystem]' option - https://postal.unavco.org/pipermail/teqc/2017/002208.html
week 1932: leap seconds - https://postal.unavco.org/pipermail/teqc/2017/002215.html
week 1936: what you can (and shouldn't) do in a RINEX obs file - https://postal.unavco.org/pipermail/teqc/2017/002229.html
week 1938: the '+psp' option - https://postal.unavco.org/pipermail/teqc/2017/002231.html
week 1939: the '+diag' option - https://postal.unavco.org/pipermail/teqc/2017/002235.html
week 1951: '-n_<system>' and SV filtering options - https://postal.unavco.org/pipermail/teqc/2017/002277.html
week 1953: more with '+diag' option - https://postal.unavco.org/pipermail/teqc/2017/002287.html
week 1954: using '+diag' output to split raw files - https://postal.unavco.org/pipermail/teqc/2017/002290.html
week 1955: current qc notation - https://postal.unavco.org/pipermail/teqc/2017/002302.html
week 1956: the '+qcq' option - https://postal.unavco.org/pipermail/teqc/2017/002304.html
week 1957: using Trimble formats - https://postal.unavco.org/pipermail/teqc/2017/002305.html
week 1958: ToC != ToE messages - https://postal.unavco.org/pipermail/teqc/2017/002310.html
week 1959: receivers vs. formats - https://postal.unavco.org/pipermail/teqc/2017/002311.html
week 1960: when the '-week' option is very wrong to use - https://postal.unavco.org/pipermail/teqc/2017/002314.html
week 1961: "less" is usually best - https://postal.unavco.org/pipermail/teqc/2017/002315.html
week 1962: using GPS L2C with teqc - https://postal.unavco.org/pipermail/teqc/2017/002316.html
week 1964: the '+eds' options - https://postal.unavco.org/pipermail/teqc/2017/002317.html
week 1965: handling RINEX comment lines - https://postal.unavco.org/pipermail/teqc/2017/002324.html
week 1966: the '+dUTC_p' options - https://postal.unavco.org/pipermail/teqc/2017/002331.html
week 1967: the strange position from '+meta' - https://postal.unavco.org/pipermail/teqc/2017/002355.html
week 1972: what shows up as metadata in RINEX headers - https://postal.unavco.org/pipermail/teqc/2017/002362.html
week 1973: GPS L2C navigation messages - https://postal.unavco.org/pipermail/teqc/2017/002363.html
week 1974: the '+ion_p' options - https://postal.unavco.org/pipermail/teqc/2017/002370.html
week 1975: the '+event' options - https://postal.unavco.org/pipermail/teqc/2017/002372.html
week 1976: options '+smtt' (default) vs. '-smtt' - https://postal.unavco.org/pipermail/teqc/2017/002374.html
week 1977: the reported interval with '+meta' for a RINEX obs file - https://postal.unavco.org/pipermail/teqc/2017/002377.html
week 1978: the '-N.dUTC' options - https://postal.unavco.org/pipermail/teqc/2017/002378.html
week 1979: the various qc elevation angles - https://postal.unavco.org/pipermail/teqc/2017/002383.html
week 1980: avoid in RINEX: Transit data - https://postal.unavco.org/pipermail/teqc/2017/002385.html
week 1981: avoid in RINEX: epoch flag = 6 - https://postal.unavco.org/pipermail/teqc/2017/002389.html
week 1982: avoid in RINEX: RCV CLOCK OFFS APPL = 1 - https://postal.unavco.org/pipermail/teqc/2018/002392.html
week 1983: don't count on in RINEX: receiver clock offset per epoch - https://postal.unavco.org/pipermail/teqc/2018/002393.html
week 1984: requirements for multiple target files/stdin - https://postal.unavco.org/pipermail/teqc/2018/002410.html
week 1985: default output for various input - https://postal.unavco.org/pipermail/teqc/2018/002412.html
week 1986: the '+latency' options - https://postal.unavco.org/pipermail/teqc/2018/002419.html
week 1987: the 'O.px and 'O.pg' options - https://postal.unavco.org/pipermail/teqc/2018/002422.html
week 1988: the '+relax' option - https://postal.unavco.org/pipermail/teqc/2018/002423.html
week 1992: the '+x_tilt' options - https://postal.unavco.org/pipermail/teqc/2018/002452.html
week 1993: GLONASS: slot and freq. chnl. numbers - https://postal.unavco.org/pipermail/teqc/2018/002453.html
week 1994: GLONASS: slot numbers > 24 - https://postal.unavco.org/pipermail/teqc/2018/002454.html
week 1995: GLONASS: signals - https://postal.unavco.org/pipermail/teqc/2018/002456.html
week 1996: GLONASS: broadcast ephemeris - https://postal.unavco.org/pipermail/teqc/2018/002457.html
week 1997: GLONASS: system time and broadcast time parameters - https://postal.unavco.org/pipermail/teqc/2018/002458.html
week 1998: qc: 'lite' vs. 'full' - https://postal.unavco.org/pipermail/teqc/2018/002470.html
week 1999: qc: the 'full' point-position and the antenna 'height' - https://postal.unavco.org/pipermail/teqc/2018/002474.html
week 2000: qc: what's a "complete observation"? - https://postal.unavco.org/pipermail/teqc/2018/002475.html
week 2001: qc: percentage of actual to expected complete observations - https://postal.unavco.org/pipermail/teqc/2018/002483.html
week 2014: qc: interpreting slips - https://postal.unavco.org/pipermail/teqc/2018/002521.html
week 2015: qc: loss-of-lock - https://postal.unavco.org/pipermail/teqc/2018/002524.html
week 2016: qc: observations per slip - https://postal.unavco.org/pipermail/teqc/2018/002526.html

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