There are a number of types of keyword based meta-data Some types with examples from MDI lev11.5 keywords are: Processing metadata source of data DPC 8- or 10-character version of data product code. DPC_CONF Indicates whether the DPC is a conforming or non-conforming DPC. DPC_CROP Crop radius in CCD pixels. DPC_FORM Image format. Possibilities are, 'Cropped', 'Raster Compressed'. DPC_OBSR DPC description. For example, 'HR_Filtergram' / High-Resolution Filtergram. DPC_ORGN Origin of data. Possibilities are 'Space', 'Sim', 'Grnd' DPC_RATE Data channel. Possibilities are 'High-Rate' (160kbps) or 'Low-Rate' (5kbps). DPC_SMPL Sample period in seconds. DPC_STR 10-character version of data product code. For example, '0x40483D00'. EPH_QUAL Status value returned by soho_ephemeris. 0 means the ephemeris data is good. SOURCE Database data source prog:mdi,level:lev1[2],series: 4b4a2d00_01h[35855]:sel[53]. SQID Sequence ID. TELESCOP SOHO. processing history ORIGIN Organization that created the FITS file. SOHO-SOI. HISTORY Comment field, usually with a comment about processing history. DATE File creation date. DSDS_UID Database ID. DSNAME SSSC data set name prog:mdi,level:lev1.5,series: hr_M_1024x500_01h[35855]. ROLL_TBL Name of roll angle table from which P_ANGLE, SOLAR_P and SOLAR_P0 are interpolated; ROLL_UPD Last modification time of the roll angle table; RUNTIME Date data was processed. Format yyyy.mm.dd_hh:mm:ss_UT TBLXYUPD Pointing table last modification date. CALTBLS Calibration files pathname. XY_FROM Source of pointing information. XY_QUAL Status value returned by mdi_pointing. 0 means the pointing data is good. AUTHOR FITS keyword. program versions BLDVER00 Level 0 software version number. BLDVER01 Level 1 software version number. BLDVER15 Level 1.5 software version number. Data descriptive name INSTRUME MDI. DATANAME Dataname is currently left blank COMMENT Comment, usually a reference to online documentation and source of data. DFNAME0 DNAME0 Descriptive name of the first variable in a data set DNOTE0 Comment field for var 0. SITE 'md' for MDI. observable DTYPE Data type. V=dopplergram B=magnetic field C=continuum M=modulation DUNIT0 Currently blank. should be copy of DATANAME for each var. BUNIT Physical units of the data. For example, m/s. DATASIGN Sign convention. The value is -1 for velocity data,... DSIGN0 Sign convention of first variable (currently the only variable). INTERVAL Integration time in seconds. X_OPAXIS Instrument field of view axis (i.e. optical axis) arc-seconds ... Y_OPAXIS Instrument field of view axis (i.e. optical axis) FD_SCALE Nominal full-disk plate scale = 1.97784. HR_MAG Magnification factor of the high-resolution... IM_SCALE Nominal pixel scale in arc-seconds/pixel. IM_SCALE = FD_SCALE/MAGNIFY MAGNIFY Magnification factor used. The value is 1 for all images other than high-resolution BFITZERO Magnetogram zero offset. MEAN_FLD Sum of B over pixels within radius (.95 * R_SUN) divided by NPIXFLUX. NPIXFLUX Number of pixels within radius .95 * R_SUN. TOT_FLUX Sum of |B| over pixels within radius .95 * R_SUN. Data mapping time axis definitions DATE-OBS Date of T_OBS in UT as DD/MM/YY. DATE_OBS UT start time of obs in CCSDS format (e.g.1996-03-19T23:07:02.000Z) TIME-OBS Time of T_OBS in UT as hh:mm:ss.ss. MDIREF T_REF as a number. I_DREC Record ID number. CADENCE Time step in seconds between adjacent data samples. ITIME GONG keyword. Same as CADENCE. T_EARTH Time of observation had it occured on Earth. T_EARTH = T_OBS + EARTH_DT. T_EPOCH Epoch for this time series. T_FIRST UT start time of observation (center of averaging interval). T_LAST UT end time of observation (center of averaging interval). T_OBS Actual (center) of integration time. T_REC Intended observation time. T_REF Local on-board time (LOBT) stamp. T_START Beginning time of first image in a data set. T_STOP Just past ending time of last image in a data set. spatial axes definitions X0 Distance along x-axis to center of solar disk from first pixel center... MDI_X0 Full Disk Image x-center in pixels. Value taken from pointing info. CENTER_X X0 + 1.0 CRPIX1 SolarSoft keyword. Disk center x-coordinate, lower left = (1,1). FNDLMBXC X-center of image in pixels. PLATE_X Pixel x-coordinate of image center. 0.5*({cols,rows} - 1) for reconstructed 2-d images. XCEN The location of the x-center of the image array on the Sun, arc-sec X_OFFSET Sampled field of view origin distance from full field of view origin. Y0 Distance along y-axis to center of solar disk from first pixel center in array pixels. MDI_Y0 Full Disk Image y-center in pixels. Value taken from pointing info. CENTER_Y Y0 + 1.0 CRPIX2 SolarSoft keyword. Disk center y-coordinate, lower left = (1,1). FNDLMBYC Y-center of image in pixels. PLATE_Y Pixel y-coordinate of image center. 0.5*({cols,rows} - 1) for reconstructed 2-d images. YCEN The location of the y-center of the image array on the Sun measured in arc-seconds Y_OFFSET Sampled field of view origin distance from full field of view origin.... CTYPE1 SolarSoft keyword. X-axis is EW on disk in arcsec from disk center. CTYPE2 SolarSoft keyword. Y-axis is NS on disk in arcsec from disk center. CDELT1 SolarSoft keyword. Same as XSCALE. PIXLENX Pixel x-dimension. 1.0 for SOI. XSCALE XSCALE = X_SCALE * IM_SCALE X_SCALE CCD pixels per bin. CDELT2 SolarSoft keyword. Same as YSCALE. PIXLENY Pixel y-dimension. 1.0 for SOI. YSCALE YSCALE = Y_SCALE * IM_SCALE Y_SCALE CCD pixels per bin. X{Y}_SCALE are the size of image ... S_ANGLE Position angle of S_MAJOR axis. Default is 0 for MDI. S_MAJOR Scale for semi-major axis of squished Earth-based images. Default is 1 for MDI. S_MINOR Scale for semi-minor axis of squished Earth-based images. Default is 1 for MDI. FNDLMBAN Angle between y-axis and major-axis in degrees. FNDLMBMA Major-axis length in pixels. FNDLMBMI Minor-axis length in pixels. map projections location of map, pointing direction, etc R_SUN Semi_major axis length of the apparent solar image ... SEMIDIAM Semi-diameter in radians. ORIENT The orientation of the Sun's image in the file/array is ... B0 Heliographic coordinate of the sub-observation point in degrees. L0 Heliographic coordinate of the sub-observation point in degrees. P_ANGLE Angular location of the solar north pole on the image after mappings have been performed. SOLAR_B0 Same as OBS_B0 - Heliographic Latitude of the observer's disk center. SOLAR_P Original position angle of the solar north pole measured eastward SOLAR_P0 Same as SOLAR_P - position angle of the Solar North pole. EARTH_B0 Heliographic Latitude of the center of the earth. EARTH_CR Heliographic rotation number for EARTH_L0. EARTH_D Sun-center to Earth-center distance in AU. EARTH_DT Delay time between T_OBS and T_EARTH (T_EARTH = T_OBS + EARTH_DT). EARTH_L0 Heliographic Longitude of the center of the earth. EARTH_R0 Radius of the Sun in arc seconds, as viewed from earth. EARTH_VN "Northward" velocity of Earth in m/s. Positive is in direction of solar north. EARTH_VR Radial velocity of Earth in m/s. Positive direction toward the Sun. EARTH_VW "Westward" velocity of Earth in m/s. Positive is in direction of Earth's orbit. OBS_B0 Heliographic Latitude of the observer's disk center. OBS_CR Carrington rotation number for OBS_L0. OBS_DIST Distance of observer to Sun center in AU. OBS_L0 Heliographic Longitude of the observer's disk center. OBS_MODE DPC description. For example, 'HR_Filtergram' / High-Resolution Filtergram. OBS_R0 Apparent semi-diameter of Sun in arc seconds from SOHO. OBS_TYPE Observable code determined from DPC. OBS_VN "Northward" velocity of observer in m/s. Positive is in direction of solar north. OBS_VR Radial velocity of observer in m/s. Positive direction is away from the Sun. OBS_VW "Westward" velocity of observer in m/s. Positive is in direction of Earth's orbit. OBT_TIME Local On Board Time of start of data. VCOR1 Observer's velocity in m/s. Data integrity quality CMPERRS Number of compression errors. MISSPKTS Number of missing packets. MISSVALS Number of missing values in data record. DATAVALS Number of non-missing values in data record. DVALS0 Number of non-missing values in all records in a data set. QUALITY Status summary, 0 == no known problems. SIZERRS Potential number of size errors from compressed data (used as a quality flag). mean and other statistics ABS_MIN Minimum of the absolute values of the data AVG_FLUX TOT_FLUX divided by NPIXFLUX. DATAKURT Kurtosis (4th moment of the data distribution). DATAMAX Maximum data value in units specified by BUNIT. DATAMEAN Mean value of data in units specified by BUNIT. DATAMEDN Approximation of data median - may not be accurate. DATAMIN Minimum data value in units specified by BUNIT. DATASKEW 3rd moment of the data distribution. DATA_RMS RMS value of data in units specified by BUNIT. D_MAX0 Maximum value of all records in a data set. D_MEAN0 Mean value of all records in a data set. D_MIN0 Minimum value of all records in a data set. D_RMS0 RMS value of all records in a data set. D_VARS Number of variables in a data set. Data structure END Mandatory FITS. Marks the end of the FITS header. SIMPLE Mandatory. File type. Mandatory in primary header. CONFORMS Used by gather_info to determine time step. DATAFILE SOI data file name. Generated by the vds library. DATAKIND Pointer to keyword list. Not fully implemented. T_BLOCK Specifies time increment that the dataset is stored (or blocked) in. PROTOCOL Conforming dataset file format. VDS_VERS VDS version number. dimensions NAXIS Mandatory. Number of axes. Must be third keyword in header. NAXIS1 Mandatory. Size of first dimension. Must follow NAXIS in header. NAXIS2 Mandatory. Size of second dimension. Must follow NAXIS1 in header. BITPIX Mandatory FITS data type. Must be second keyword in header. number representation BLANK Undefined integer pixels are set to this value. BSCALE Scaling factor to convert data to float. FITS only. BZERO Offset applied to true pixel values. FITS only.