  A collaboration between the W. M. Keck Observatory (WMKO) in Hawaii and the
NASA Exoplanet Science Institute (NExScI) in California, the Keck Observatory
Archive (KOA) was commissioned in 2004 to archive observing data from WMKO,
which operates two classically scheduled 10 m ground-based telescopes. The
observing data from Keck is not suitable for direct ingestion into the archive
since the metadata contained in the original FITS headers lack the information
necessary for proper archiving. Coupled with different standards among
instrument builders and the heterogeneous nature of the data inherent in
classical observing, in which observers have complete control of the
instruments and their observations, the data pose a number of technical
challenges for KOA. We describe the methodologies and tools that we have
developed to successfully address these difficulties, adding content to the
FITS headers and "retrofitting" the metadata in order to support archiving Keck
data, especially those obtained before the archive was designed. With the
expertise gained from having successfully archived observations taken with all
eight currently active instruments at WMKO, we have developed lessons learned
from handling this complex array of heterogeneous metadata that help ensure a
smooth ingestion of data not only for current but also future instruments, as
well as a better experience for the archive user.
