Processing

Newclkcorr

Clock Corrections at Parkes

The GPS and GPS Common-view are the methods used to refer measurements made using the Parkes observatory clock ("UTC(PKS)") to Universal Coordinated Time (UTC). The offset between the Mark IV Parkes clock and the time standard of the Global Positioning System (GPS) is measured by the Totally Accurate Clock 2 system. Transfer from GPS time to UTC is done by applying offsets reported by the Paris observatory of le Bureau International des Poids et Mesures (BIPM) in Circular T. The offset between the Parkes Mark IV clock and the National Time Scale, UTC(AUS), which is Australia's realisation of UTC, is derived from the caesium clocks at the National Measurement Institute (NMI). The clock tie is performed using a common-view GPS service provided by the NMI. Transfer from UTC(AUS) to UTC is possible via the offsets reported in Circular T. These methods of the clock corrections commenced on the MJD 50844. Previously used scheme of linking Parkes clock to the UTC is described here.

Currently used scheme is fully integrated into tempo2, where fairly regularly sampled values of the offset between pairs of clocks are recorded in ASCII text files, one pair per file. The files begin with a sequence of one or more comment lines beginning with '#', the first of which specifies the name of the clock to convert from, followed by the name of the clock to convert to (e.g. UTC(PKS) UTC(GPS) means the file contains UTC(GPS)−UTC(PKS)). The remainder of the file comprises one line per sample, each consisting of the MJD and the offset in seconds, separated by whitespace. Given a measurement made with one clock, a sequence of file names and a desired clock to which to refer the measurement, corrections can be made by adding the terms with the appropriate signs (see the tempo2 manual for operational details). The simple file format facilitates visualisation by generic plotting utilities, and basic manipulation with standard unix tools. Custom utilities include update_clkcorr, which imports and pre-processes data from external sources, and compare_clkcorr, which constructs difference values for an arbitrary collection of clock pairs, interpolated to a common set of equally spaced MJD samples, and outputs the result in ASCII format for plotting or further processing.

Procedure to update the clock corrections

The primary repository of clock correction data is the tempo2 clock directory: $TEMPO2/clock. Before doing anything else, do a CVS update in $TEMPO, $TEMPO2, and $CVSHOME/soft_atnf/atas/clkcorr.

  • pks2gps.clk : Contains UTC(GPS)−UTC(PKS), obtained using the GPS East monitoring system. To update:
1. Get the raw monitoring log from a Parkes computer, at /nfs/online/timing/pkclk00/pkclk00.YYYY (YYYY = the current year), and place it in $CVSHOME/soft_atnf/atas/clkcorr/gps.
2. Run update_clkcorr -t pksgps6 pkclk00.YYYY in the same directory. If parsing errors are encountered (an example is shown below), edit the file and fix or delete the faulty line, and re-run update_clkcorr. Then go to $TEMPO2/clock and check pks2gps.clk.new for sanity. Copy it to pks2gps.clk.
3. Commit pkclk00.YYYY and pks2gps.clk to the CVS repository, with a comment (including your name if done as pulsar).
For example: cvs ci -m 'smith: updated up to 1 Jan 2007' pks2gps.clk

Parsing errors can include lines inserted at the start of the clock corrections (underneath the commented lines) which do not fit the MJD order. Eg.
#>Thu Jan 6 14:46:16 2011 Imported from file pkclk00.2010
#Comments from merged data file:
#>Fri Jan 14 16:46:24 2011 Imported from file pkclk00.2011
#Comments from merged data file:
#>Mon Jan 24 10:41:01 2011 Imported from file pkclk00.2010
0.00694 0.000001130467
50844.72917 -0.000000749068
50845.77083 -0.000000747637
50846.81250 -0.000000746650

  • gps2utc.clk: Contains UTC−UTC(GPS), as reported in Circular T. To update:
1. Go to $CVSHOME/soft_atnf/atas/clkcorr/cirt and list the available files. Then download any further Circular T files available from here.
2. Run update_clkcorr -t gpsutc cirt.* in the same directory, check gps2utc.clk.new for sanity in $TEMPO2/clock, and copy it to gps2utc.clk. (the list can be shorter if you are sure certain cirt files have already been incorporated, however this is not essential: overlapping merges are handled properly).
3. Commit cirt.* and gps2utc.clk to CVS.
  • nist2utc.clk: Contains UTC−UTC(NIST), as reported in Circular T. To update, follow the procedure above for gps2utc.clk, but change the command in step 2 to update_clkcorr -t nistutc cirt.*

If you are using tempo instead of tempo2, you will have to update $TEMPO/clock/time.dat. To do this, go to $TEMPO/clock/ directory and run the backward-compatability program:

make_time_dat -m MJD >> time.dat

where MJD is the Modified Julian Day after the final entry in time.dat. You will also need to update $TEMPO/clock/utccorr.tot using the following command (or similar):

awk '{if ($1 > MJD) printf " %8.2f %18.1f\n", $1, $2*1e9}' < $TEMPO2/clock/nist2utc.clk >> utccorr.tot

Both files contain a dummy entry for MJD 60000, which you will need to move to the bottom of the file with a text editor. Double-check both files for continuity over the transition from old to new data, then commit them to CVS.

To update the common-view clock correction scheme (see above), the following files are necessary instead of pks2gps.clk and gps2utc.clk:

  • pks2aus.clk : Contains UTC(AUS)−UTC(PKS), obtained using the common-view system. To update:
1. Go $CVSHOME/soft_atnf/atas/clkcorr/common_view and list the available files. Then get any newer files from the raw monitoring logs from a Parkes computer, at /nfs/online/timing/common_view/daily_reports/parkes.?????
2. Run update_clkcorr -t pkscv parkes.????? in $CVSHOME/soft_atnf/atas/clkcorr/common_view directory, check pks2aus.clk.new for sanity, and copy it to pks2aus.clk. (again, the list can be shorter if you are sure certain files have already been incorporated, however this is not essential: overlapping merges are handled properly).
3. Commit parkes.????? and pks2aus.clk to CVS.
  • aus2utc.clk: Contains UTC−UTC(AUS), as reported in Circular T. To update, follow the procedure above for gps2utc.clk, but change the command in step 2 to update_clkcorr -t ausutc cirt.*
  • tai2tt_bipmYYYY.clk: Go to the TT(BIPM) website, and search for the latest TTBIPM.YY.ext (rename the file if necessary). Then go to $TEMPO2/clock and update the end of the latest tai2tt_bipmYYYY.clk, using the command:
    -->awk '{mjd=substr($0,1,5); d=substr($0,20,7); if (mjd > ##### && mjd < 60000) printf "%.1f %.9f\n", mjd, 32.184+d*1e-6;}' < TTBIPM.YY.ext >> $TEMPO2/clock/tai2tt_bipmYYYY.clk

    Note: In the command above, you will need to change 3 parts of the command - ##### to the last MJD on the tai2tt_bipmYYYY.clk; TTBIPM.YY.ext to the latest update file eg. TTBIPM.10.ext; tai2tt_bipmYYYY.clk to the current clock file eg. tai2tt_bipm2011.clk
  • Next, log into pisces (located at Parkes) as pulsar:
1. Go to $TEMPO2/clock , and check the status of the files by doing cvs stat (be careful of files needing merging). If everything is ok, then run cvs update to reload all the clock files that have just been updated
2. Go to $TEMPO/clock, then cvs update time.dat and utccorr.tot
3. Go to $TEMPO2/earth, and update eopc04_IAU2000.62-now
  • Update the files on SourceForge