In normal operation, data are exported from LPO on tapes in FITS format (`tapes' include Exabyte and DAT cartridges). There is now (and has been for some time) a commitment to write the tapes in a way that conforms strictly to the FITS standard, for both the images and headers. This document describes how, for the case of the WHT, information describing the observation should be coded as FITS headers.
For several years there has been some uncertainty as to how FITS header-records specific to particular observatories, and not defined in the FITS standard, should be formatted. At one point it looked as if the `hierarchical-keywords' proposal would provide the answer, but this proposal was not adopted as a standard. It now seems to be accepted that the correct approach is for observatories to devise new keywords for each header item, the only constraints on these keywords being that they should be consistent with the generalized rules for keywords, and not conflict with mandatory or reserved keywords.
We have tried to follow the guidelines specified in the FITS standard for constructing new keywords, which suggests that keywords should be shortened by truncation if necessary. Where appropriate we have based the WHT FITS keywords on those in use at the AAO and UKIRT, or keywords expected by data-reduction programs in the IRAF environment. We have taken the document issued by the NASA Office of Standards and Technology[1] as the definitive description of the FITS standard.