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Parkes Clock Corrections for TEMPO (Outdated procedure)

Obtaining Parkes Clock Corrections for TEMPO (Outdated procedure)

NOTE

The clock corrections scheme has been updated and it is documented here. The procedures below should not be followed as they may contaminate time.dat with errors.

UTC CORRECTIONS - TIME.DAT and UTCCORR.TOT

Pulsar timing at Parkes relies on knowing the precise time of the Observatory 1PPS pulse. Several different reference clocks are available. The clock correction system described here refers the Parkes clock to UTC(NIST) and to UTC as defined by the BIPM. The data to make these corrections in TEMPO are stored in two files:

time.dat contains the offsets: UTC(PKS) - UTC(NIST)
utccorr.tot contains the offsets: UTC - UTC(NIST)

Both files are normally kept under CVS control in $TEMPO/clock/, that is, $PSRHOME/runtime/tempo/clock/.

The Parkes 1PPS is generated by the MkVIb clock which is driven by the Observatory hydrogen maser frequency standard. It is approximately aligned with UTC using the Parkes GPS system. There are several GPS clocks monitored by the MkVIb clock - currently we are using the GPS East receiver, which is mounted on the Telecom tower to the east of the telescope, as a reference. Offsets between the Parkes 1PPs and the GPS 1PPS are monitored every second by the observatory clock system. These data are averaged and recorded by the 'DESK' computer in /nfs/online/timing/pkclk00.

The differences UTC - UTC(NIST) and UTC - UTC(GPS) are monitored and recorded by the BIPM.

Procedure for updating clock correction files

Clock correction files and programs are under CVS control with the repository at Epping. To checkout the repository, do the following on any ATNF machine:

cd $CVSHOME
cvs co soft_atnf/atas/clkcorr

Ensure that the executables are up-to-date:

cd $CVSHOME/soft_atnf/atas/clkcorr
make

Then follow the procedure outlined below to generate the clock correction files required by TEMPO:

Set the clkcorrdir environment variable:
setenv clkcorrdir $CVSHOME/soft_atnf/atas/clkcorr/

Copy recent PKS - GPS clock offsets to the working directory:
cp /nfs/online/timing/pkclk00.log $clkcorrdir/gps/mk6.log

The next step is to form 1-hour averages from these values
```
cd $clkcorrdir/gps
mk6_av
```
This will produce a file mk6.tmp.

Move mk6.tmp to mk6.av. This file contains occasional bad lines and it is desirable to remove them at this stage. Use
```
mk6_plt
```
to examine the data. (-h for help.)
Only entries not already processed need be in $clkcorr/gps/mk6.av, but it is convenient to keep one file per year. At the end of each year, move $clkcorr/gps/mk6.av to $clkcorr/gps/mk6_YYYY.av for archival.

Get recent Circular T files from the BIPM. Click publication to see a list of the cirt.NNN files available, then:
```
cd $clkcorrdir/cirt
ftpcirt NNstart [NNstop]
```
where NNstart and NNstop are the numbers of the first and last Circular T files needed, respectively. If the optional NNstop is omitted, only cirt.NNstart is downloaded. ftpcirt will automatically add the new files to the repository.

Extract the clock offsets: UTC - UTC(NIST); and UTC - GPS and copy or append them to cirt.dat as follows:
```
getcirt cirt.NNN >> cirt.dat
```
Ensure that there are no duplicated lines in cirt.dat. (If the format of Circular T changes, it may be necessary to alter the sed instructions in getcirt to extract the required information and nothing else.) Note that cirt.dat must cover the same MJD range as gps.dat.
To create files in the format of the clock offset files required by tempo, run:
```
cd $clkcorrdir
pkstime  
```
This creates the files time.tmp and utccorr.tmp. Start and stop MJDs are optional... do pkstime -h for help.
Note, it is important to check these files for significant discrepancies from smooth changes in the offsets. These occur occasionally and may be genuine, but more often are due to a failure of the GPS monitoring system or some other problem.
Copy these files to $TEMPO/clock (normally $PSRHOME/runtime/tempo/clock/). Check that the local versions of time.dat and utccorr.tot are up-to-date, and then append time.tmp and utccorr.tmp, respectively, to them. Delete any repeated entries and then CVS check in these files. (Note: utccorr.tot currently has a gap from June 1995 to Jan 1998. Anyone who wishes to fill this gap may do so.)

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

Last update: 22 March 2004 - Dick Manchester

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