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 MDJ 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:
- 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.
- Run update_clkcorr -t pksgps6 pkclk00.YYYY in the same directory. If
parsing errors are encountered, 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.
- 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
- gps2utc.clk: Contains
UTC−UTC(GPS), as reported in Circular T. To update:
- Go to $CVSHOME/soft_atnf/atas/clkcorr/cirt
and list the available files. Then download any further Circular T
files available from
here.
- 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).
- 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 3 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 > 53184) 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:
- 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.?????.
- 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).
- 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 3 to
update_clkcorr -t ausutc cirt.*.
Last update: 2007 February 06 — Lucyna Chudczer
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