[IGSMAIL-5272]: Switch the absolute antanne model within the IGS

[Gerd Gendt]

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IGS Electronic Mail      19 Dec 05:26:06 PST 2005      Message Number 5272
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Author: Gerd Gendt


Dear colleagues,

At the meeting in San Francisco the IGS Analysis Centers (AC) representatives
have discussed the  switch to the new absolute antenna model. We came up with
the following  decisions:

1. ANTEX file:

1.1 The new antenna model is accepted by all the ACs. An updated offset for
    the  PRN17 will be added. 
    New satellites will be added just after launch with default values (block
    mean)  and updated as soon as possible.

    JPL has agreed to make some more validations with their GRACE-based model.
    The final long-term goal should be the generation of a model which
    includes also LEO derived PCV maps to have one unique model for ground-
    and space-based applications including nadir angles to up to 16 degrees.

1.2. The GLONASS PCV and offsets will be delivered by CODE.

1.3 The ANTEX file name will have the following structure:
    base_wwww.atx, e.g. igs05_1325
    where 
    base - basic name which will only be changed if existing values are
           changed (one exception is a new launched satellite for which the
           initial values  will be updated in the first weeks)
    wwww - is the GPS-week where the last information were added.


1.4 Satellite antenna x-, y-offsets:
    A unified definition for all satellites and systems will be applied.
    The definition will be that one used for Block II/IIA namely:
    - z-axis points to the geocenter
    - y-axis is cross product of z-axis and sat-sun direction (in that order)
    - x-axis completes a right-handed system (x is pointing to the sun)

    All adaptations will be done by corresponding settings in the ANTEX file. 
    With the new ANTEX format, having all information in one place, the ACs
    have not to  maintain different files with x-y-z offset and this way one
    source of  inconsistency is removed.

2. ANTEX and SINEX-block GPS_PHASE_CENTER

   To enable the tracking of information about physically calibrated antennas
   in  the SINEX file the following proposal should be discussed:

   The new SINEX 2.00 already states (Remark 11):
     Take value S/N '-----' if the phase center offsets apply to all antennas
     of the same type.
   The new proposal goes one step further and states:
     Take radome 'NONE' if the phase center offsets apply to all antennas of
     the same type.

   Practically the following sequential test has to be applied to obtain for a 
   given specific antenna the valid (used) PCV:

   1. Check ANT + RADOME + S/N       , if not found
   2. Check ANT + RADOME + '-----'   , if not found
   Proposal: 
   3. Check ANT + NONE + '-----' (valid for all not explicitly given Radomes) 

      The test is to apply for searching in the atx-file and in the SINEX
      block  GPS_PHASE_CENTER.


      Example:
      +SITE/ANTENNA
      *SITE   P      ____DESCRIPTION_____ _S/N_ 
       STA1  A  .... ASH701945B_M    SCIS 12345    --------
       STA2  A  .... ASH701945B_M    SCIS CR519    -----   |
       STA3  A  .... ASH701945B_M    OSOD 020      --   |  |
      -SITE/ANTENNA                                  |  |  |
                                                     |  |  |
      +SITE/GPS_PHASE_CENTER                         |  |  |
      *____DESCRIPTION_____ _S/N_                    |  |  |
       ASH701945B_M    NONE -----          STA3   <--   |  |     
       ASH701945B_M    SCIS -----          STA2   <-----   |
       ASH701945B_M    SCIS 12345     for  STA1   <--------
      -SITE/GPS_PHASE_CENTER

4. SINEX with SATA_Z

   In the new SINEX 2.0 new parameters for satellite antennas are defined. It
   is recommended to include as a minimum the SATA_Z parameter in the SINEX
   file. The parameter should be constrained so that the submitted solution is
   based on  the given standards.

5. Satellite clocks

   The antenna model used to for generating the clocks is given in the
   following  comment line:

5.1 SP3:
   This information is not only for the clocks of interest.
   /* ANTENNA MODEL USED: igs05_1325  CLOCKS ALIGNED TO: igs05_1325  
   /* ANTENNA MODEL USED: jpl_2005    CLOCKS ALIGNED TO: igs05_1325  

5.2 CLK-RINEX:
   Following comment lines:
   ANTENNA MODEL FOR ANALYSIS       : igs05_1325  
   ANTENNA MODEL FOR CLOCK ALIGNMENT: igs05_1325  

6.The switch to the new APCV model will done in parallel with the switch
  to ITRF2005 (APR/MAY 2006).

Best regards
Gerd Gendt

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*                         Gerd Gendt                                         *
*  _/_/_/  _/_/_/_/_/_/   GeoForschungsZentrum                               *
* _/       _/       _/    Department Geodesy and Remote Sensing              *
* _/ _/_/  _/_/    _/     Telegrafenberg A17                                 *
* _/    _/ _/     _/      D-14473 Potsdam ,  GERMANY                         *
*  _/_/_/  _/    _/_/_/   Phone : ++49 331 288 1114   Fax :++49 331 288 1759 *
*                         E-Mail: gendt at gfz-potsdam.de                       *
* IGS GFZ AC         :    AFTP://ftp.gfz-potsdam.de/pub/igsprod              *
*                         http://www.gfz-potsdam.de/igs                      *
* IGS Analysis Coord.:    AFTP://ftp.gfz-potsdam.de/pub/igsacc               *
*                         http://www.gfz-potsdam.de/igsacc                   *
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