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'.
Note: In 2010, the Bulletin B format has been changed
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. Check this into CVS.
The required data is obtained from Section 1 of the new Bulletin B (DAILY FINAL VALUES ... find bulletinb.nnn and rename it to B.nnn). Then use the script getut1.2010 to extract UT1-UTC for every fifth day and put it in the file ut1.tmp.
The instructions are:
- Get the latest Bulletin B and copy it to $clkcorrdir/iers/B.nnn.
- Extract the required UT1 - UTC offsets using the script `getut1.2010`
- This produces a file ut1.tmp in the /iers directory
- 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.
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
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
Please report errors or problems with these clock correction procedures to Dick Manchester.
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.
- Old instructions: For old Bulletin B files, the instructions were to extract the values from Section 2 of Bulletin B (SMOOTHED VALUES ... using bulletinb_IAU2000.nnn and rename it to B.nnn). The script `getut1' extracted UT1R - TAI for every 5th day and placed it in the file ut1.tmp.