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When a new scan is prepared4 at the telescope, the
associated IMB-FITS file name is constructed with the current
date. Later in this process (up to several minutes after), the scan is
actually started5, and the current date and
time are used to build the MJD-OBS and DATE-OBS in the
FITS Primary header. If those two steps are performed exactly before
and after midnight respectively, the file name and the Primary header
refer to 2 different dates, e.g.
iram30m-fts-20120809s323-imb.fits:
MJD-OBS = 56149.0038078704 / MJD at observation start
DATE-OBS= '2012-08-10T00:05:29.000'
For several purposes, Mrtcal saves the observing date and time
of each file in the index. In order to deal correctly with the above
issue, it is decided to:
- save the date as found in the file name, so that there is no
difference for the user between the file name and the date exposed
by MRTCAL,
- the time value saved for this file refers to the above date.
The direct consequence of those 2 rules is that, in case of the
midnight issue exposed above, the UT value will be larger then
24h. Note that the UT value associated to each file is saved for
bookkeeping purpose, e.g. for analysis of the calibration though date
and time. It is considered as a typical value for the whole scan. Each
individual spectrum produced by MRTCAL uses its own date and time.
In details, the observing date saved in the index is used:
- to check the entry uniqueness (date, scan and backend triplet
should be unique),
- to sort the entries (by date, scan and backend),
- through the command MFIND /DATE,
- in the output of the command MLIST,
- in the Sic variables MDX%DOBS and MHEAD%KEY%DOBS
and the associated UT value is used:
- to sort the entries,
- in the output of the command MLIST,
- in the Sic variables MDX%UT and MHEAD%KEY%UT
The user should be ready to encounter UT values larger than 24h in the
MLIST output and larger than in the Sic variables.
Next: MRTCAL Language Internal Help
Up: IRAM Memo 2014-? Mrtcal
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2014-07-01