[IGSMAIL-1829] CODE Analysis Changes

Fri Mar 13 06:14:41 PST 1998

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IGS Electronic Mail      Fri Mar 13  6:14:41 PST 1998      Message Number 1829
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Author: T.A. Springer
Subject: CODE Analysis Changes

Dear IGS colleagues,

 Starting this week a number of (IGS) processing "standards" 
 have been changed.

  For the CODE analysis this means the following changes:
    - Reference frame changes:
      - ITRF96 coordinates,
      - ITRF96 velocity field,
      - Use of a subset of 37 of the new set of 47 feference stations

        The 11 feference sites not used:
        --------------------------------
        TROM: No data. Receiver and Antenna are being replaced(?)
        NYAL: No data. Receiver and Antenna are being replaced(?)
        MADR: Site no longer used due to severe data problems in 1997
        MASP: Strong 14-day periods in our solutions
        MALI: 40 mm U difference between ITRF96 and CODE
        FAIR: 20 mm U difference between ITRF96 and CODE
        GODE:-20 mm U difference between ITRF96 and CODE
        TIDB: 25 mm U difference between ITRF96 and CODE
        OHIG:-18 mm N difference between ITRF96 and CODE
        DAV1:-10 mm N difference between ITRF96 and CODE
        KERG:-12 mm E difference between ITRF96 and CODE

        The 37 sites which are constrained (1 mm):
        ------------------------------------------
        ALGO AREQ BRAZ BRMU DRAO FORT GOLD GRAZ GUAM HART HOB2 IRKT 
        KIT3 KOKB KOSG KOUR KWJ1 LHAS MAC1 MATE MDO1 NLIB ONSA PERT 
        PIE1 POTS REYK SANT SHAO THU1 TSKB VILL WES2 WTZR YAR1 YELL 
        ZWEN

        **** Note that we selected one additional site: REYK

      - The ITRF96 reference frame is realized by constraining the
        positions of the 37 selected sites to 1 mm (this used to be
        0.1 mm). This means that the sites may actually move by
        several millimeters.

    - Site coordinate model change:
      - Ocean loading (finally) included based on values from
        Dr. H.G. Scherneck.

  Estimated CODE product changes
  ==============================

    We estimated the changes in our products (orbits, coordinates 
    and ERPs) caused by the above modification, by processing five days 
    with the old and the new strategy (day 060-064 of 1998).
    The consistency between the results is very high as you can
    see from the table below.

                        DX    DY    DZ     RX    RY    RZ   SCALE  RMS 
                       (mm)  (mm)  (mm)  (mas) (mas) (mas)  (ppb)  (mm)
    CRD 060 NEW-OLD      0    -3    -6   -0.1  -0.0  -0.3    0.5    8.9
    CRD 061 NEW-OLD     -2    -1    -4   -0.1  -0.0  -0.3    0.4    8.8
    CRD 062 NEW-OLD     -1    -1    -4   -0.1  -0.0  -0.3    0.4    8.3
    CRD 063 NEW-OLD      1    -2    -4   -0.1  -0.0  -0.3    0.3    7.9
    CRD 064 NEW-OLD      3    -3    -3   -0.1  -0.0  -0.2    0.1    7.5

    ORB 060 NEW-OLD      2     2     1    0.23 -0.11 -0.40   0.1   20.0
    ORB 061 NEW-OLD      0     1     4    0.17 -0.13 -0.40   0.0   20.0
    ORB 062 NEW-OLD      1     2     6    0.14 -0.06 -0.37   0.0   20.0
    ORB 063 NEW-OLD      2     0     5    0.10 -0.02 -0.38   0.0   10.0
    ORB 064 NEW-OLD      0    -2     2    0.13 -0.03 -0.34   0.0   10.0

    ERP 060-064 NEW-OLD                   0.07 -0.17  

    As noted already by the ACC (Jan Kouba) the change from ITRF94 to
    ITRF96 causes small rotations around Y (-0.2 mas) and Z (-.2 mas).
    Both effects can clearly be seen in our orbit (ORB) and
    ERP results above (note the RX and RY have a
    different meaning for the orbit than for the ERPs).
    The Z-rotation is also clearly observed in the coordinate (CRD)
    differences. The CRD results also show a small scale difference
    which indicates that the scale between ITRF94 and ITRF96 is
    slightly different, or at least that our realization of the
    two ITRF's is different.

    The entire CODE ERP series from day 200/1993 to today has been
    recomputed using the above reference frame realization. Over the
    entire period of 4.5 years the offset between the ITRF94 and 
    ITRF96 series are:
      - X   (ITRF96-ITRF94) : -0.037 mas
      - Y   (ITRF96-ITRF94) : -0.075 mas
      - LOD (ITRF96-ITRF94) : -0.004 md/day

    An updated AC questionaire (CODE.ACN) has been send to the IGSCB and the
    ACC. It is also available on our anonymous ftp (directory CODE).

Kind regards,
        Tim Springer, Markus Rothacher and Stefan Schaer
        CODE Analysis Center

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 Tim Springer                       Astronomical Institute, University of Berne 
 Tel:   +41 31 6318592              Sidlerstrasse 5, CH-3012 Bern, Switzerland  
 Fax:   +41 31 6313869              ftp: ubeclu.unibe.ch  -or-  130.92.6.11
 e-mail: springer at aiub.unibe.ch          after login: cd aiub$ftp
 www:   http://www.cx.unibe.ch/aiub/
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[Mailed From: TIM SPRINGER <SPRINGER at aiub.unibe.ch>]