[teqc] helpful tip of week 2018

Lou Estey lou at unavco.org
Wed Sep 12 08:06:29 MDT 2018


This week's tip: qc: signal-to-noise

The qc of signal-to-noise was not in the original qc algorithms.  In fact, in
the mid-1990's, the RINEX observable S1 and S2 fields (signal-to-noise on GPS L1
and L2 carrier frequencies, respectively) were not even officially defined in RINEX,
although several translators back then were quietly outputting signal-to-noise
using these fields.  To complicate matters, there was also not a consistent unit
of signal-to-noise being used by manufacturers.  Circa 2001, plus or minus
depending on the manufacturer, there was trend to report signal-to-noise in
units of decibel-Hertz (dBHz), which is now the norm.

The current strategy in teqc for showing the general signal-to-noise is very simple:
take the mean and standard deviation of each Sn, n = 1, 2, 5, 6, 7, 8, for all values
if qc 'lite', or only for values above the cutoff mask angle (default of 10 degrees)
if qc 'full' (e.g. see tip of the week https://postal.unavco.org/pipermail/teqc/2018/002470.html
for an explanation of 'lite' and 'full').  Then in the qc report one might see
something like this where the Sn are in units of dBHz:

Mean S1                 : 48.37 (sd=5.05 n=118645)
Mean S2                 : 44.92 (sd=5.21 n=85011)
Mean S5                 : 50.11 (sd=4.57 n=46399)
Mean S7                 : 50.03 (sd=4.69 n=30836)
Mean S8                 : 52.60 (sd=4.71 n=26282)

In the parentheses after each mean, there is also the standard deviation and the number
of values found.  And in the next version of teqc to be released, there will also be
a signal-to-noise summary line, SSN, showing the means on one line.  The following are
for Receiver 1 mentioned in last week's tip of week on multipath rms:

Receiver 1:
       first epoch    last epoch    sn1   sn2   sn5   sn7   sn8
SSN 18  8 25 00:00 18  8 25 23:59 48.37 44.92 50.11 50.03 52.60

Being a modern receiver, the above mean and standard deviation values are in units of dBHz.
For completeness, here are the SSN results for the same other three receivers mentioned
last week:

Receiver 2:
       first epoch    last epoch    sn1   sn2   sn5   sn6   sn7   sn8
SSN 18  8 25 00:00 18  8 25 23:59 43.84 41.29 48.35 47.91 47.47 50.79

Receiver 3:
       first epoch    last epoch    sn1   sn2   sn5   sn7   sn8
SSN 18  8 25 00:00 18  8 25 23:59 43.80 40.44 48.63 47.46 51.09

Receiver 4:
       first epoch    last epoch    sn1   sn2   sn5   sn6   sn7   sn8
SSN 18  8 25 00:00 18  8 25 23:59 45.60 40.93 47.67 47.43 47.16 49.81

(Reminders: Receivers 2 and 4 were capable of tracking the Galileo E6 signal, so
S6 signal-to-noise shows up for these two.  And all four receivers are sharing
the same signals from a single antenna via a splitter.)

Important note: if the RINEX observation file being qc-ed does not contain the
observable Sn, n = 1, 2, 5, 6, 7, or 8, then teqc uses the 0-9 signal-to-noise flags
on the corresponding phase values Ln as a proxy, and then you might see something like
this:

Mean S1                 : 7.59 (sd=0.89 n=114082)
Mean S2                 : 6.98 (sd=0.91 n=84993)
Mean S5                 : 7.86 (sd=0.83 n=46399)
Mean S7                 : 7.88 (sd=0.87 n=26282)
Mean S8                 : 8.24 (sd=0.78 n=26282)
...
       first epoch    last epoch    sn1   sn2   sn5   sn7   sn8
SSN 18  8 25 00:00 18  8 25 23:59  7.59  6.98  7.86  7.88  8.24

In the long qc report, one can also find the signal-to-noise for each carrier frequency
grouping in a table and elevation-binned histogram, e.g. for S1:

S/N L1 summary (per elevation bin):
elev (deg)  tot SN1 sig    mean          2|0       4|0       6|0       8|0
  85 - 90    436   4.352   53.992 ##|||||||||||||||||||||||||
  80 - 85   1280   3.216   54.328 ##|||||||||||||||||||||||||
  75 - 80   3298   3.046   54.241 ##|||||||||||||||||||||||||
  70 - 75   4662   2.841   53.783 #||||||||||||||||||||||||||
  65 - 70   5888   2.521   53.888 #||||||||||||||||||||||||||
  60 - 65   6043   2.531   53.398 #||||||||||||||||||||||||||
  55 - 60   6667   2.388   53.179 #||||||||||||||||||||||||||
  50 - 55   7079   2.320   52.570 #|||||||||||||||||||||||||
  45 - 50   7735   2.442   51.594 #|||||||||||||||||||||||||
  40 - 45   8257   2.362   50.684 #||||||||||||||||||||||||
  35 - 40   9625   2.443   49.263 #||||||||||||||||||||||||
  30 - 35   9563   2.343   47.825 #|||||||||||||||||||||||
  25 - 30  10670   2.313   46.436 #||||||||||||||||||||||
  20 - 25  11805   2.395   44.761 #|||||||||||||||||||||
  15 - 20  12083   2.601   42.760 #||||||||||||||||||||
  10 - 15  13554   2.638   41.239 #||||||||||||||||||||
   5 - 10  15303   2.721   39.423 #|||||||||||||||||||
   0 -  5   9820   3.242   38.022 ##|||||||||||||||||
     <  0      7  11.556   25.843 ######|||||||

where the '|' histogram symbols go out to the mean for the SV elevation range and
the '#' (or '=') histogram symbols show the standard deviation for the SV elevation
range.  In the above histogram one can readily see the signal-to-noise dropoff with
decreasing SV elevation.

As with multipath rms, I'm often asked about what constitutes a "good" or "bad"
signal-to-noise mean.  As with multipath, I'd have to say that it depends.

But, again as with multipath rms, monitoring for changes over time in signal-to-noise at a
permanent station can be very useful.  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 signal-to-noise.  Likewise, if there's been no equipment or firmware
or configuration changes, and you see a consistent change in signal-to-noise over time,
this is probably a good argument to look for a root cause, which might be:

- a degrading antenna low-noise amplifier (LNA), resulting in a slow decrease in
   signal-to-noise over one or more frequencies
- a degrading antenna cable connection (due to corrosion?), resulting in a slow
   decrease in signal-to-noise
- natural growth increase around the site esp. when affecting the sky view from the
   antenna, resulting in a slow decrease in signal-to-noise

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
week 2017: qc: multipath rms - https://postal.unavco.org/pipermail/teqc/2018/002527.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://postal.unavco.org/pipermail/teqc/attachments/20180912/36bcb469/attachment-0001.html>


More information about the teqc mailing list