From jimr@maia.usno.navy.mil Tue Mar 23 12:13:19 EST 1999
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From: Jim Ray (USNO 202-762-1444) 
Message-Id: <199903231708.MAA20181@maia.usno.navy.mil>
Subject: Update of clock RINEX format
To: gpst@maia.usno.navy.mil
Date: Tue, 23 Mar 1999 12:08:10 EST
X-Mailer: Elm [revision: 212.4]
Status: RO

Practical experience in developing the new software needed to combine
satellite and receiver clock values for the IGS (work that Jan Kouba
has been doing) has shown the need for a few modifications to the clock
RINEX format:

   1) Clock offsets as comment -- As agreed among the Analysis Centers,
      the official IGS values for the satellite antenna offsets (Z-
      components) should be provided in a header comment record.

   2) Clock ref using GPS time -- Some ACs use a particular receiver
      as their fixed clock reference, but then re-align all clocks to
      broadcast GPS time.  In this case, it is misleading to indicate
      only the analysis clk ref.  So the format has been modified to
      allow this option to be documented.

   3) Multiple reference clocks -- While a linear combination of more
      than 1 clock can be held fixed as the analysis reference and this
      is allowed in the clock RINEX format, the ACs are asked *not* to
      use this option for their IGS submissions.  Doing so would
      complicate the clock combination greatly.  However, different
      clocks can be used as reference for different intervals during the
      same day (e.g., if the usual reference has a data gap).  The header
      records have been modified to allow for this possibility.

   4) PRN list -- To aid in reading the clk files, a list of satellites
      used in the analysis has been added to the file header.

A complete copy of the updated clock RINEX format is available at
http://maia.usno.navy.mil/gpst/clock-format .

I would like to thank Jan for all his efforts in developing the clock
combination software, as well as the Analysis Centers who have been
providing valuable practical experience.

Best regards,
--Jim