Standardizing Documentation of FITS Headers Although the FITS file format[1] can be self-documenting, human intervention is often needed to read the headers to write the necessary transformations to make a given instrument team’s data compatible with our preferred analysis package. External documentation may be needed to determine what the values are of coded values or unfamiliar acronyms. Different communities have interpreted keywords slightly differently. This has resulted in ambiguous fields such as DATE-OBS, which could be either the start or mid-point of an observation.[2] Conventions for placing units and additional information within the comments of a FITS card exist, but they require re-writing the FITS file. This operation can be quite costly for large archives, and should not be taken lightly when dealing with issues of digital preservation. We present what we believe is needed for a machine-actionable external file describing a given collection of FITS files. We seek comments from data producers, archives, and those writing software to help develop a single, useful, implementable standard. http://virtualsolar.org/ 218.48 J.A. Hourclé NASA-GSFC (Wyle) joseph.a.hourcle@nasa.gov Goal: Create a documentation standard that : • Does not require modifying existing FITS files. • Is machine-readable. • Can be used by software developers to integrate new missions & instruments with minimal effort. The documentation should: • Identify which keywords are using a registered FITS standard and which are discipline, mission, instrument, or processing specific. • Provide units if not explicitly given • Identify range of possible values • Provide expansion / explanation of enumerations • Provide free text to describe how to interpret coded values (eg, SDO ‘QUALITY’), or for additional details. • Identify the authoritative value from a group of similar values. (thus identifying which values are derived, and have more error) References: [1] Pence, et.al. 2010, “Definition of the Flexible Image Transport System (FITS), version 3.0”, http://dx.doi.org/10.1051/0004-6361/201015362 [2] Rots, et.al, (in preparation), “Representations of Time Coordinates in FITS Time and Relative Dimension in Space (V1.0) “, http://hea-www.cfa.harvard.edu/~arots/TimeWCS/ [3] Derriere, et.al, “Vocabularies in the Virtual Observatory, Version 1.19”, http://www.ivoa.net/documents/latest/Vocabularies.html [4] W3C, “Simple Knowledge Organization System“, http://www.w3.org/2004/02/skos/ [5] NASA, “Fits Keyword Dictionaries”, http://fits.gsfc.nasa.gov/fits_dictionary.html [6] NASA HEASARC, (untitled) http://heasarc.gsfc.nasa.gov/docs/fcg/standard_dict.html [7] NOAO, “NOAO FITS Keyword Dictionary: Version 1.0”  http://iraf.noao.edu/iraf/web/projects/ccdmosaic/imagedef/fitsdic.html [8] Shimojo, “The List of SOLAR-B”Hinode” Mission-Wide FITS Keywords”, http://hinode.nao.ac.jp/sbsc/SB_MW_Key13.pdf [9] W3C, “SKOS Simple Knowledge Organization System Primer”, http://www.w3.org/TR/skos-primer/ FITS ‘Keyword Dictionaries’ Although there are many ways of documenting FITS keywords, a number of missions use a ‘keyword dictionary’.[5] The structure varies, as there is no single standard for these documents. For example: [6,7,8] KEYWORD: BITPIX REFERENCE: FITS Standard STATUS: manditory HDU: any VALUE: integer RANGE: -64,-32,8,16,32 COMMENT: bits per data value DEFINITION: The value field shall contain an integer. The absolute value is used in computing the sizes of data structures. It shall specify the number of bits that represent a data value. NAME: Image.naxis[i] KEYWORD: NAXIS%d DEFAULT: none INDEX: 1-9 HDU: primary & extension VALUE: %d UNITS: COMMENT: Number of pixels along axis EXAMPLE: 2048 DESCRIPTION: Required FITS format keywords. Header Keyword: NOAA_NUM Format : Integer Unit/Option : - Category : SOLAR-B Data Source : Chief observer or Proposer of the observation Sample : 11345 Description : The NOAA number of the active region. Note : If the target region doe