[teqc] Clock slips and multipath

Lou Estey lou at unavco.org
Tue Sep 11 10:01:41 MDT 2018


dear Khadidja,

Thanks for sending the bskr1591.98o file.  The header line in the file:
ASRINEXO V2.9.10LH  ANONYMOUS           17-MAY-06 11:15     PGM / RUN BY / DATE
shows that the translator used was Werner Gurtner's old ASRINEXO software.

1. The connection between multipath slips and n-millisecond clock jumps is
explained in tip of the week https://postal.unavco.org/pipermail/teqc/2018/002521.html
You can switch from doing clock n-millisecond slip detection (the default)
to not doing them by including the '-cl' option, e.g. from `teqc +help`:

     +cl[ock_slips]           do clock n-msec slip detection (default)
     -cl[ock_slips]           don't do clock n-msec slip detection

but if you use '-cl' during qc, then the 'C' indicators merely change to 'M'
indicators (MP1 and MP2 or MP15 and MP51 slips, though in this old GPS data
M means both MP12 and MP21 slips).  It's really the same problem due to a
translation error.

2. Technically, the time of clock (ToC) of the GPS navigation message need not
be the same as the time of ephemeris (ToE) of the GPS nav message, but checking
for inequalities -- especially in older data -- is a very good way of screening out
problematic navigation messages.  In this case, there is such a problem as
collected by the Ashtech Z12 receiver at bskr for one nav message for PRN 24.
If you use the combined broadcast messages for 1998-159 at CDDIS, for example,
you do not see this message because the combination process has weeded out this
error (if it had been collected anywhere else and submitted to CDDIS).

3. This gets back to the original error in the translation done by ASRINEXO and
question 1.  Without the original raw Ashtech data, there isn't anything teqc can
do to fix this.

Hope this helps.

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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On 11-Sep-18 08:32 AM, khadidja Sekkour wrote:
> Dear Lou,
> 
> I really don't now, but I think that they use WinPrism (Ashtech GPS survey software). I asked the operator if there was a translation error, he said that at that time they use an other software to check the quality of the translation but the result was the same.He think that the gap of 780.000 seconds was caused by damaged cable.
> 
> I have two days to process 159 and 160 and I am trying to find an explanation of:
> - 1. Why clock slips are MP1 and MP2 slip (as presented in TEQC's manual) despite in bskr1591.98s there is no effect of multipath (MP1 and MP2 are about 0.37 and 0.42 m)
> - 2. Warning ! NAVSTAR GPS SV G24: ephemeris ToC != ToE (extracted from bskr1601.98s)
> - 3. Notice ! reversing msec phase adjustment upon rx msec clock reset in 'bskr1601.98o'
> 
> Could you please give me more explanation about these questions.
> PS: Please find attached the observations files related to 159 and 160.
> Best regards,
> Khadidja,
> 
> --------------------------------------------------------------------------------
> Khadidja SEKKOUR
> Engineer on Geodetic sciences and Topography
> Département de Géodésie Spatiale
> Centre des Techniques Spatiales
> Agence Spatiale Algérienne
> 01 Avenue de la Palestine BP13
> Arzew, Oran 31200
> Algeria
> E-mails: khadidja.sekkour at gmail.com; s_khadidja2007 at yahoo.fr
> 
> ________________________________________
> De : Lou Estey [lou at unavco.org]
> Date d'envoi : mardi 11 septembre 2018 14:06
> À : khadidja Sekkour
> Cc: teqc at postal.unavco.org
> Objet : Re: Clock slips and multipath
> 
> Given the one teqc Notice message during the qc:
> ! Notice ! reversing msec phase adjustment upon rx msec clock reset in 'bskr1591.98o' ...
> and all the clock slip indicators in the ASCII time plot, e.g.:
> 
>    SV+--------|--------|--------|--------|---------|--------|--------|--------+ SV
>     1|        __CCCCCCCCCCCC-__         __-CCCCCCCCCC-_                       |  1
>     2|CCCCCCC-_                               __-----___           _-CCCCCCCCC|  2
>     3|                       __-CCCCCCCCCCCCCCCCCCC-_                         |  3
> 
> my guess is that there was a translation error, which would have been common enough
> for Ashtech data back in the 1990's.
> 
> What created the bskr1591.98o RINEX file?
> 
> --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
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> On 09-Sep-18 04:37 PM, khadidja Sekkour wrote:
>> Dear Lou,
>>
>> Please find attached the QC full report of the station of Bskr.
>> The result of teqc +qc -nav bskr1590.98n +plot bskr1591.98o command line indicates an increase of the sampling rate of about 780 sec at 12:45
>>
>> ! Notice ! reversing msec phase adjustment upon rx msec clock reset in 'bskr1591.98o' ...
>> qc full >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>! Notice ! 1998 Jun  8 12:45:00.000: poss. incr. of sampling int. OR data gap of 780.000 seconds (min. dt found= 30.000 s)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>> version: teqc  2017Jul3
>>
>> Could you please explain to me why clock slips are MP1 and MP2 slip.
>>
>>
>> --------------------------------------------------------------------------------
>> Khadidja SEKKOUR
>> Engineer on Geodetic sciences and Topography



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