[teqc] helpful tip of week 1908

Lou Estey lou at unavco.org
Wed Aug 3 07:27:56 MDT 2016


This week's tip: doppler observables and RINEX L2 observables

Last week's tip about using the '+C2', '+L5', "+L6', '+L7', '+L8', or '+all'
options mentioned that doppler observables are not included: these options
are only shortcuts for amending the default observable list for phase,
pseudorange, and signal-to-noise observables when reading raw data.

If you want doppler observables when reading raw data, then you must use
the '-O.obs' option and specify all observables that you want in the output,
including those of doppler.

Why is doppler not included?  Well, it appears that there is very little
need for doppler anymore.  About 10 or so years ago I was told that the
only use case remaining where doppler helps in position solutions is in
RTK applications where the base station is non-stationary.  (I have no
idea whether this is still true; someone may wish to comment.)

At any rate, here at UNAVCO we routinely create RINEX that is made available
on our ftp server and very little of it has doppler: it would only have doppler
if the data supplier sent RINEX to us with doppler in it.  Our software for
creating RINEX from raw data leaves out doppler by default, and many of
the sites we handle are used as reference stations for other users, such
as surveyors.  And we have very few requests for RINEX with doppler.

My take-away from the past 10 years: doppler observables are not important
for almost all GPS/GNSS users that we service.

-----------

It is probably also worth repeating from last week that using the '+C2' option,
or including the C2 observable with the '-O.obs' option, effects whether or not
the '+L2C_L2' or '-L2C_L2' options work as you expect; see 2009 Aug 3 entry in
http://www.unavco.org/software/data-processing/teqc/log/log.html

    - using '+C2' or '-O.obs' with C2: '+L2C_L2' and '-L2C_L2' are ignored; the
      L2 (and S2, D2) are based on L2(L2C) if present, based on L2(P2) otherwise

    - using '-C2' and '-O.obs' w/o C2: '+L2C_L2' or '-L2C_L2' takes effect,
      allowing pure L2(L2C) or pure L2(P2), respectively; default would continue
      to be -L2C_L2, i.e. RINEX L2 (and S2, D2) based on L2(P2)

So, for GPS or QZSS, if you use '+C2' or include C2 with '-O.obs', then RINEX L2
will be from L2C for those SVs broadcasting L2C (assuming the receiver is set to
track L2C and log its data); otherwise, RINEX L2 will be from the L2P(Y) signal.

But, if you are tracking GLONASS G2SA (roughly speaking, the GLONASS analogue to
GPS L2C), then the options '+L2C_L2' and '-L2C_L2' currently operate independently
from whether or not you use '+C2' or include C2 with '-O.obs'.   (An aside: I have
considered including new options that would probably be called '+G2SA_L2' and
'-G2SA_L2' to separate out the functionality between GPS/QZSS L2C and GLONASS G2SA,
but so far there hasn't really been a clear need to do this.)

Also, if teqc translates GPS/QZSS L2P(Y) or L2C or GLONASS G2HA or G2SA, the
RINEX L2 phase observable is not modified in any way from the original format
(except to get it into units of L2- or G2-cycles).

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




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