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Updating ut1.dat

Updating the ut1.dat file

The ut1.dat file contains the corrections made to UT1R-TAI time which is used by the Tempo and Tempo2.
To maintain timing precision it is necessary to update the ut1.dat file on a regular basis. The corrections are published monthly by the International Earth Rotation Service (IERS) in several IERS bulletins . The IERS bulletins page contains the latest and earlier versions of Bulletin B, which can be selected from the Products section under '>Bulletins B, C, D'.

It is also important to keep the Earth orientation parameters up to date. This is done by downloading the eopc04_IAU2000.62-now from http://hpiers.obspm.fr/iers/eop/eopc04_05/ to $TEMPO2/earth directory.

The ut1.dat File

The ut1.dat is found in the tempo directory. Below is a typical end section of this file.

     51079 311508  311555  311604  311698  311769  311837
     51109 311908  311969  312052  312148  312221  312295
     51139 312361  312427  312516  312579  312636  312686
     51169 312720  312775       0       0       0       0                     2
END

format for final entry (if incomplete):
     48949 268419  268505  268590  268675  268760       0                     5
END
Last entry: B.131

Columns 2 to 7 list the UT1R-TAI corrections in units of 0.1 ms. The following key may be useful in explaining the format of this file.

 51139      312361        312427    312516  312579  312636    312686
UT date    correction    correction    ...     ...     ...    correction
	  at MJD 51139  at MJD 51144                         at MJD 51164

Updating ut1.dat

The required data are obtained from Section 2 of Bulletin B (SMOOTHED VALUES ...use bulletinb_IAU2000.nnn and rename it to B.nnn). The script `getut1' extracts UT1R - TAI for every 5th day and places it in the file ut1.tmp. Instructions are as follows:

Get the latest Bulletin B and copy it to $clkcorrdir/iers/B.nnn.
Extract the required UT1 - UTC offsets using the script `getut1'
```
%getut1 B.nnn
```
This produces a file ut1.tmp in the iers directory.
NOTE: Some messing around is necessary after a leap second has been introduced. First, getut1 is run on the B bulletin which contains the leap second adjustment and ut1.tmp saved. The value of nleap (= TAI-UTC) in the file $clkcorrdir/iers/iers.awk must then be adjusted to the new value of TAI-UTC (it is usually increased by 1; the current value is listed in Circular T). Then getut1 is run on the same B bulletin and ut1.tmp concatenated with the saved ut1.tmp. The concatenated file must then be edited to have a unique and correct value of the offset for each time. Offsets before the leap sec will be correct in the first file and offsets after the leap sec will be correct in the second file.
cd to $TEMPO2/clock/ and check that the local version of ut1.dat is up to date. Then copy $clkcorrdir/iers/ut1.tmp to $TEMPO2/clock/ and merge it with the tail of ut1.dat. This requires some care, but there are normally overlapping entries which make the procedure fairly obvious. See above for the format of the last line. Make sure you update the 'Last entry' line.
If you are using TEMPO, there is a link in $TEMPO/clock directory to the updated ut1.dat.
Finally CVS check in the new version of ut1.dat in $TEMPO2/clock/ directory.

Please report errors or problems with these clock correction procedures to Dick Manchester.

Last update: 8 April, 1999 - Dick Manchester (rmanches@atnf.csiro.au)

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