Subject: JSOC keyword definitions - some starting thoughts From: Rick Bogart Date: Tue, 10 Jan 2006 15:25:03 -0800 To: Rasmus Munk Larsen CC: Neal Hurlburt , Karen Tian , Jesper Schou , Phil Scherrer HMI/AIA JSOC DRMS keywords 1. I suggest that for purposes of avoiding ambiguity, the internally-defined keywords used in the DRMS be specifically designed to avoid conflict wirh keywords used in existing analysis environments (e.g. SOI SSSC. GONG++, SolarSoft). Since these environments are based on files with FITS keywords, the easiest way to avoid conflict is to make sure that no internal keywords comply with the FITS standard. That is easily achieved, since the FITS standard limits the character set for keywords to the character set [A-Z,0-9,'-','_'], as well as limiting the length of keywords to 8 characters. VOTables are of course much more permissive, virtually any string can probably be parsed as a name field, though the use of double quotes '"' and angle brackets '<>' would probably only invite trouble. I suggest that internal keywords be formed from the ASCII printing character set 0x20-7e with the exception of the '$' sign (interpreted differently in other countries), and that all keywords include at least one lower case alphabetic character ([a-z]) or one punctuation character other than '- or '_'. Further desiderata: To the extent possible, the keywords should support, in the sense of unambiguous one-to-one mappings, and in order of preference, the FITS World Coordinate System, the VSO data model, and the SPASE data model (http://www.igpp.ucla.edu/spase/). Common abbreviations within keywords: GC Geocentric HC Heliocentric HG Heliographic SC Spacecraft-centered 2. Coordinate systems 2a Data Structure Dimensions the number of independent dimensions in the data structure; equivalent to FITS NAXIS Length[n] the length of dimension n in the data structure; equivalent to FITS NAXISn ReferencePoint[n] the coordinates of the reference point: the pixel number along the nth axis to which location information refers; equivalent to WCS CRPIXn PixelIncrement[n] the increment in physical units per pixel along the nth axis at the reference point; equivalent to WCS CDELTn CoordinateType[n] the name of the physical unit corresponding to the nth dimension of the data structure; equivalent to WCS CTYPEn 2b Time CreateDate the date and time of creation of the data record; equivalent to FITS DATE ObservationTime the date and time of the (weighted) center of the observing interval during which the data were taken; equivalent to VSO Observation_Time ExposureTime the length of the exposure time for a single (component) observation DataDuration the (weighted) duration of all component observations; equivalent to VSO Duration StartTime the date and time at which the observation or component observations commenced StopTime the date and time at which the observation or component observations ended 2c. Location ObserverGCLatitude the geocentric latitude of the observer at ObservationTime ObserverGCLongitude the geocentric longitude of the observer at ObservationTime ObserverGCAltitude the geocentric distance of the observer at ObservationTime ObserverHGLatitude the heliographic latitude of the observer at ObservationTime ObserverHGLongitude the heliographic longitude of the observer at ObservationTime ObserverHCDistance the heliocentric distance of the observer at ObservationTime ObserverHCVRadial the heliocentric radial velocity of the ObserverHCVWest the heliographic westward velocity of the ObserverHCVNorth the heliographic northward velocity of the TargetHGLatitude the heliographic latitude of the data reference point; for certain appropriate CoordinateType's equivalent to WCS CRVALn TargetHGLongitude the heliographic latitude of the data reference point TargetHCHeight the heliocentric distance of the data reference point TargetHCPositionAngle the heliographic position angle of the data reference point TargetSCX the X-coordinate of the data reference point in spacecraft coordinates TargetSCY the Y-coordinate of the data reference point in spacecraft coordinates SphericalMapping the name or reference identification of the spherical coordinate mapping transformation used 2d. Spectral ObservingWavelength ObsBandMinWavelength ObsBandMaxWavelength BandMinFrequency BandMaxFrequency 3. Instrument diagnostics/information ObservatoryName the name of the observatory, spacecraft, or network from which the original data were taken; if the data are based on observations from multiple sources, InstrumentName the name of the telescope or instrument DetectorName ObservingProgramName 4. Data statistics and quality 4a. Statistics (N.B. These keywords assume univariate data in the record; if data are multivariate, separate keywords would be required for each variable.) InvalidValue the numeric representation for missing ValidValues the number of valid (non-missing) data ActualMinimum the minimum value of data in the record ActualMaximum the maximum value of data in the record ActualAbsMinimum the minimum absolute value of data in the record ValidMinimum the minimum potentially valid value for data ValidMaximum the maximum potentially valid value for data ValidAbsMinimum the minimum potentially valid absolute value for data DataMean the arithemetic mean of the data values in the record DataMedian the median value of the data values in the record DataStdDev the standard deviation of the data values in the record DataVariance the variance of the data values in the record DataSkewness the skewness (normalized 3rd moment) of the data values in the record DataKurtosis the kurtosis (normalized 4th moment) of the data values in the record 4b. Quality 5. Processing history InstituteName the name of the organization producing the data record 6. etc. PhysicalObservable