Written by Ken Ebisawa, February 8, 2002
HTML Last Updated: May 13, 2003
The arrival time correction was made making use of the clock correction measurements which had been carried out regularly at each ground contact. Precise time for each superframe was calculated by interpolating the two ground contacts before and after the data was taken. The ground clock correction record for the entire GINGA period is kept at clkfeduc.list, which was made by Kazumi Asai.
Under normal circumstances, the time difference for each superframe before and after the correction is several milliseconds for the contact pass, or several tens of milliseconds for the remote pass.
From time to time, time correction is not very precise, for example, when the two adjacent clock measurements were not available, or the ground clock was reset. The maximum amount of the time correction made for a superframe is put in the FITS header MAXTDIFF. MAXTDIFF values for all the files are shown in the file check_max_tdiff.log. If this value is too large (say, >100 msec), users might not expect accurate time correction. If MAXTDIFF is 0.0, that means time correction was not possible by some reason. See the "Accuracy of Ginga Time Assignment" report by H. Negoro for the clock information at the KSC ground station during the GINGA operation. Note that the time assignment problems reported in this report (p.18) have been fixed in the present time correction.
In the following, we list the names of the FRF which had MAXDIFF values 0.0 or larger than 1500 msec. Please be careful when using these data sets for timing analysis.
| FRF | MAXTDIFF | REASONS |
| FR870305.R0927.fits | 0.0000 | Initial operation, no prior clock correction. |
| FR870305.S0910.fits | 0.0000 | Initial operation, no prior clock correction. |
| FR870305.S0913.fits | 0.0000 | Initial operation, no prior clock correction. |
| FR870305.S0916.fits | 0.0000 | Initial operation, no prior clock correction. |
| FR870305.S0920.fits | 0.0000 | Initial operation, no prior clock correction. |
| FR870305.S0923.fits | 0.0000 | Initial operation, no prior clock correction. |
| FR870331.S0513.fits | -1988.9619 | Initial operation, clock unstable? |
| FR870417.R1548.fits | 0.0000 | Wrong time assignment in the original file. |
| FR870421.S0946.fits | -8011.8066 | Too large clock rate (KSC clock problem). |
| FR870504.S0632.fits | 7054.0020 | Long gap between clock corrections (KSC clock problem). |
| FR870628.S0428.fits | -4008.5459 | KSC clock problem. |
| FR870628.S0611.fits | -1803.6646 | KSC clock problem. |
| FR870709.R1548.fits | 0.0000 | Wrong time assignment in the original file. |
| FR890105.S0121.fits | -2081.8398 | Long gap between clock correction (end of year). |
| FR890329.S0715.fits | -2001.8613 | Only one superframe had a wrong time (corrected). |
| FR890413.S0305.fits | 0.0000 | Wrong time assignment in the original file. |
| FR890627.S1029.fits | 1927.6113 | Several superframes had originally wrong time. |
| FR890712.S0513.fits | 1530.3770 | Only one superframe had a wrong time (corrected). |
| FR890906.S0306.fits | 0.0000 | Wrong time assignment in the original file. |
| FR891212.S0306.fits | -2005.5562 | Original time assignment wrong (corrected). |
| FR910417.R0001.fits | -1613.3687 | Original time assignment wrong (corrected). |
| FR910417.S0046.fits | -1615.4668 | Original time assignment wrong (corrected). |
| FR910417.S1101.fits | -1517.9771 | Original time assignment wrong (corrected). |
| FR911029.R1235.fits | 0.0000 | Final data. No clock correction after. |
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