[teqc] helpful tip of week 2016

Lou Estey lou at unavco.org
Thu Aug 30 10:10:34 MDT 2018


This week's tip: qc: observations per slip

The qc of observations per slip, or '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

is from the original qc algorithms, developed by others at UNAVCO in the early and
mid 1990's for GPS-only data.  Back at that time, the typical GPS data collected
was 30-second sampling, both for campaign work and the initial permanent stations
being installed.  Typical obs/slip numbers were considered to be around 400 or
higher for data with a tolerable number of slips.  (If, per chance, there are zero
slips detected, then a value of 1 slip is assumed to avoid division by zero.)

The above SUM line is for data collected at 1-second sampling on a new receiver
that we happen to be testing right now, so assuming the same occurrence rate of
slips per unit time as in those golden, olden days, one would expect an obs/slip
value on the order of 12000 or higher, which is about what we see.

However, if we saw an obs/slip value significantly below 12000 for 1-second sampling,
say, 6000 or 3000, does this mean the data are faulty or the receiver is bad?

No, not necessarily, not by a long shot.  The real metric of whether data is good
is whether it can be (post)-processed or not with acceptable errors on whatever
parameter(s) are important to the end user, say, the position uncertainty or rms
if looking at many positions.  Seeing a lower than expected obs/slip value is
merely an indicator of a possible problem.  Sometimes, just the tracking of
one or two problematic SVs can drive the number of slips up, driving the obs/slip
value down, but after elimination of those SVs (which would probably occur automatically
for most modern processing software) all is well.

Or consider the following case.  A manufacturer recently contacted me about the
following situation involving the same site, same receiver and antenna hardware
with 1-second sampling, but with a firmware change:

old firmware:
SUM 18  2 13 00:00 18  2 13 23:59 24.00   1 1175089 1173702 100  0.27  0.29 195617

new firmware:
SUM 18  2 13 00:00 18  2 13 23:59 24.00   1 1311928 1311544 100  0.27  0.23   8983

A user of this receiver type had contacted the manufacturer about their obviously
quite terrible new firmware because the obs/slip value from teqc had dropped so much.

The manufacturer sent me both datasets (from which I generated the qc myself) and,
not paying much attention to the obs/slip value, I was stuck by how great the data
was collected using both the old and the new firmware.  So what's going on?

In this particular case, note that the multipath rms was equally good with both
firmwares.  Also the receiver in both cases was tracking essentially 100% of the
expected observables.  But, also note the significant _increase_ in the number of
observables using the new firmware -- more than an 11% increase from the old firmware.

Comparing the ASCII time plots it was quite clear that the new firmware was doing
a much better job at tracking at low elevations than the old firmware, but with the
expected increase in loss-of-lock, and therefore also slips, at those lower elevations.
Including those extra slips at low elevation deflated the obs/slip value.

But both datasets were, in my opinion, very good.

Does this mean that the obs/slip value is useless?  No, it can be very useful.
Let's look at another case.  Next we'll be looking at recent chronological SUM lines
from CEDA, a site in the Basin and Range, with 15-second sampling:

SUM 18  6 30 00:00 18  6 30 23:59 24.00  15 137842 134841  98  0.27  0.22   4350
SUM 18  7  1 00:00 18  7  1 23:59 24.00  15 138067 134909  98  0.29  0.24   7100
SUM 18  7  2 00:00 18  7  2 23:59 24.00  15 133950 130527  97  0.29  0.23   2105
SUM 18  7  3 00:00 18  7  3 23:59 24.00  15 137184 133289  97  0.29  0.23   1960
SUM 18  7  4 00:00 18  7  4 23:59 24.00  15 136227 131949  97  0.27  0.23   2275
SUM 18  7  5 00:00 18  7  5 23:59 24.00  15 135667 131225  97  0.28  0.21   4374
SUM 18  7  6 00:00 18  7  6 23:59 24.00  15 135488 131949  97  0.28  0.22   5075
SUM 18  7  7 00:00 18  7  7 23:59 24.00  15 138493 135460  98  0.28  0.22   2605
SUM 18  7  8 00:00 18  7  8 23:59 24.00  15 137900 135045  98  0.28  0.23   2813
SUM 18  7  9 00:00 18  7  9 23:46 22.85  15 125986 114954  91  0.28  0.22   2613
SUM 18  7 10 04:57 18  7 10 19:08 9.050  15     -     723  -     -     -       1
SUM 18  7 11 01:57 18  7 11 18:51 11.93  15     -    1560  -     -     -       5
SUM 18  7 12 03:05 18  7 12 23:59 13.75  15     -     956  -     -     -       3
SUM 18  7 13 00:00 18  7 13 23:05 12.67  15     -    6972  -     -     -       8
SUM 18  7 14 00:39 18  7 14 21:50 15.27  15     -    6437  -     -     -      24
SUM 18  7 15 00:09 18  7 15 22:10 16.43  15     -    9849  -     -     -       6
SUM 18  7 16 00:45 18  7 16 22:56 16.65  15     -    9206  -     -     -       6
SUM 18  7 17 02:11 18  7 17 20:10 13.53  15     -   10988  -     -     -       7
SUM 18  7 18 00:16 18  7 18 23:23 18.16  15     -    8118  -     -     -      21
SUM 18  7 19 00:29 18  7 19 20:11 15.78  15     -    7116  -     -     -       9

Obviously there are numerous indicators even on the SUM lines that something went
very wrong at CEDA late in the day of 9 July 2018.  But let's suppose you were
collecting various qc stats, day by day, and that the obs/slip value was one of
those stats.  The precipitous drop to low obs/slip values from 10 July onward
would have been enough to signal that the site was in serious trouble.  (UNAVCO
staff will be going to CEDA as soon as possible.  I suspect that something was
nearly fried due to a nearby lightning strike, either the LNA of the antenna or
the receiver.)

Therefore, monitoring the obs/slip and looking for decreases over time is a very
good strategy for flagging a potential problem.  But determining exactly what the
problem might be is a different issue -- for example, consider what you would now
think if the drop in the obs/slip coincided with a firmware change in the receiver?

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://postal.unavco.org/pipermail/teqc/attachments/20180830/464aceb2/attachment-0001.html>


More information about the teqc mailing list