We have duplicated (to the second!) the observation times
listed in early computer printouts produced by Copernicus
principal investigators by adding the first SET time
to the GMT observation times listed in the raw and coadded scan data files.
The feeling is that our listed observation times refer to the time
the Copernicus satellite crosses the longitude of the ascending node
(i.e., LAN). It is still unclear however whether this reference time refers
to the orbit in which the observation was made or to the orbit in which
the data was last dumped.
In any event, the actual calculations for deriving the start and end
observation times (from the IDL program coptime.pro), which are based on data
extracted from the Copernicus raw data files, are as follows:
ddate = (yr_obs-1900)*1.0D+03 ; decimal date
+ day_obs + (hr_obs/24.0D0)
fst = (frst_set * 15.72887)/(24.0*3.6D03) ; first SET time in days
lst = (last_set * 15.72887)/(24.0*3.6D03) ; last SET time in days
startobs = ddate(i)+fst(i) ; start time
endobs = ddate(i)+lst(i) ; end time
The SET times mentioned above refer to Spacecraft Equivalent Time (SET)
and represent units of 15.72887 seconds.