This file is a the present draft keywords document. It will likely change. SOI level-2 input keywords The keywords needed for level-2 processing are divided into several groupings. The keywords have been chosen to avoid collisions with FITS standard keywords and SOHO adopted keywords. In general we have adopted different keywords even when SOHO has a similar keyword function to avoid double meanings. Some of these keywords describ attributes of the entire dataset and some describe all data for a particular variable and some for each record of each variable. They are all listed here for completeness. Keywords found in conforming dataset overview files have an "o" in col 1. Keywords found in conforming dataset per-record header files have an "r" in col 2. Keywords found in conforming dataset data files have an "d" in col 3. Indexing rd I_DREC SOI record number or other index unique to each record rd T_REC SOI Nominal time for data record. T_REC will normally only occur in level-1.5 and above datasets. It should be expressed in UT. Time OBT_REF SOI LOBT from CCD header in TAI seconds. OBT_REFC SOI Corrected OBT_REF, gross errors removed. OBT_DP SOI Data Product time in LOBT OBT_OBS SOI Time of observation with drifts corrected, seconds TAI T_REF SOI OBT_REF as ascii date - as TAI T_REFC SOI OBT_REFC as ascii date - as TAI T_DP SOI OBT_DP as ascii date - as TAI r T_OBS SOI UT time of observation (center of averaging interval). All times with OBT_XXX names are in LOBT TAI seconds. T_REF and T_DP are the intended LOBT, not corrected for SOHO LOBT drifts. Thus the LOBT values are traceable back to telemetry packets. T_DP will usually be the same as T_REF for Dynamics and Structure program data but shifted by 30 secs for Campaign data. LOBT times are ascii "floats" and are in seconds from the SOHO TAI epoch which is the CCSDS standard of 1 January 1958 (EID-A, 3.3.9.2). r T_EARTH SOI UT time if observation had been made from Earth o T_FIRST SOI T_OBS of start of data o T_LAST SOI T_OBS of end of data All times with T_XXX names are in the SOI ascii time format which is: yyyy.mm.dd_hh:mm:ss.ss_ZZ where the timezone part "_ZZ" is optional and defaults to "_UT". The fractional second part may be omitted or may have as many digits as are needed. T_OBS or T_EARTH will usually be used by Level-2 processing. T_OBS is the UT time at SOHO that corresponds to the center of the averaging interval over which the observable was measured. T_OBS is corrected for all known errors. T_FIRST and T_LAST are the times of the first and last "image" in a set of data. EXPTIME SOI&soho The CCD EXPosure Time for a filtergram (secs). r INTERVAL SOI Integration time in seconds. CADENCE SOI Interval between measurements in a set (seconds). Durations are always recorded in seconds (fits floats). The CCD_EXPT value will usually only be present when the data is individual filtrgrams. INT_TIME is the duration of the set of filtergrams that make up the observable quantity. E.g. for Dynamics, INT_TIME is almost 60 seconds and synoptic magnetograms have INT_TIME of usually 300 seconds. For individual filtergrams INT_TIME is the same as CCD_EXPT. DATE fits file creation date DATE-OBS fits UT 'DD/MM/YY' date of observation These names may be present (TBD) but will not be used by any SSSC program DATE_OBS soho UT start time of obs in CCSDS format DATE_END soho UT end time of obs in CCSDS format These will be present and will be T_FIRST and T_LAST in CCSDS format OBT_TIME soho LOBT of start of data OBT_END soho LOBT of end of data These will be present and will be DP_TIME of the first and last observables of a set of data. They will be in the same format as DP_TIME. DEL_TIME soho delta time within obs in seconds since DATE_OBS DEL_TIME will be computed as T_SOHO - T_FIRST. "Record-axis" and "Series-axis" blocking information When datasets are stored as time series several parameters are specified to allow record and dataset location. These four parameters are the same for all datasets in a given dataseries and are found in the Oracle DataSetName table as well as in the overview files. o T_UNITS SOI Specifies the "units" of the "record-axis" and the data_series "axis" of the dataset. In the case of times, the units are always seconds and the T_UNITS parameter specifies the kind of time. Examples are: 'UT' and 'LOBT'. T_UNITS is also the units for T_OBS, T_FIRST, and T_LAST. o T_EPOCH SOI Specifies epoch for this time series. The epoch can be used to find the nominal time for any record. T_EPOCH is stored as a string. o T_BLOCK SOI Specifies the "time" increment for dataset within the data_series. T_BLOCK is stored as a string. Typical examples are for hourly blocked data, '1h' or equivalently '60m' or '3600s'. o T_STEP SOI Specifies the number of seconds per record for an equally spaced series. Observer location. The observer location will be available in several coordinate systems. At least two heliocentric systems will be used. One is the normal Carrington system as defined by Lord Carrington. Three quantities are required, the heliographic longitude, the heliographic latitude, and the rotation number. A second derived coordinate system will also be used. This will be a heliocentric frame which rotates with a period of 365.2425 days and which has its zero longitude in the direction of the first point of Aries at the time of the Vernal Equinox in the year TBD. In this system the longitude of the disk center will vary in a 4 degree range during the year. We may want to move the reference date to center the excursion about zero. Since this derived system is easily calculable from the Carrington system, it will be done inside the level-2 mapping functions when needed. r OBS_B0 SOI Carrington Latitude of the observer's disk center. r OBS_L0 SOI Carrington longitude of observer's disk center. r OBS_CR SOI Carrington rotation number for OBS_L0. EARTH_B0 SOI Carrington Latitude of the center of the Earth. EARTH_L0 SOI Carrington longitude of the center of the Earth. EARTH_CR SOI Carrington rotation number for EARTH_L0 EARTH_CT SOI "Carrtime" OBS_CT SOI "Carrtime" Note that these are digits "0" not letters "o". For compatibility with customary usage, B0 and L0 are given in degrees in the ascii forms. r OBS_DIST SOI Distance from observer to sun center in AU. EARTH_AU SOI Distance of center of Earth from center of Sun, AU. Observer Velocity r OBS_VR SOI Radial velocity of observer in m/s, plus is away from sun. r OBS_VW SOI "Westward" velocity of observer in m/s. plus is in direction of Earth's orbit. r OBS_VN SOI "Northward" velocity of observer in m/s. Plus is motion toward solar north. Pointing r X0 SOI Location of solar disk center in pixel coordinates. r Y0 SOI Location of solar disk center in pixel coordinates. The coordinate system for these disk center locations is the memory order for the image array as read from the file, with the first pixel as (x,y) location of (0,0) and the second pixel addressed as (1,0). Scale r X_SCALE SOI Pixel scale along the x-axis in Nominal_pixels/pixel. r Y_SCALE SOI Pixel scale along the y-axis in Nominal_pixels/pixel. The coordinate system for X_SCALE and Y_SCALE is the same as for X0 and Y0. For MDI, these will likely be fixed for the mission and will come from the calibration data made using the Air Force Target. These ({XY}_SCALE) parameters should account optical and detector characteristics. They will be the same or nearly the same for MDI but may differ for GONG if rectangular pixels are used. They reflect the deviations from a nominal pixel scale for the image. Typical values are 1.0, 1.0. These are the geometrical optics scalings. No account is made for distortions or refraction. r IM_SCALE SOI Nominal pixel scale in arc-seconds/pixel. The Image Scale in arc-sec per pixel is independant of axis in the image. It can be used along with a standard SOI definition of the Solar radius in arc-seconds so that the apparent radius in pixels will be e.g. 959.627/(IM_SCALE*OBS_DIST). Orientation The orientation of the Sun's image in the file/array is defined by a character string indicating the "side" of the sun that corresponds to the origin and x-axis used for the pointing and scale parameters. This string contains 4 characters from the set N,S,E,W and tells the "corner" for the (0,0) pixel and the corner for the (xmax,0) pixel. In the soho nominal image orientation this would be "SESW". This orientation assumes the solar position angle is zero. The actual position angle of the solar pole is then given in the "X0,Y0" coordinate system. r ORIENT SOI Orientation string, e.g. 'SESW' r SOLAR_P SOI Position angle of the Solar North pole.(degrees) The P angle is measured counterclockwise from the plus-y axis and is reported in radians. A picture showing the "nominal" image orientation can be of great help here. The P_angle here is the angular location of the solar north pole on the image after mappings are done for {XY}0, {XY}SCALE, and ORIENT to produce SESW, in order. If the image is not stored SESW then SOLAR_P will not describe the pole position in the as-stored orinetation. Normally, ORIENT will indicate an intention and will not change within a given dataset, rather SOLAR_P may have a range of 0:360 in the case of rotating images. Thus the set SESW, SWNW, NWNE, NESE will all be shown as SESW with SOLAR_P corrected as needed. Similarly, the set SWSE, SENE, NENW, NWSW will be converted to SWSE with corresponding corrections to SOLAR_P. Refraction Parameters Since we want the level-2 programs to operate on ground based data as well as MDI space data we must also include the definition of possible image scale due to atmospheric refraction. The following scale parameters will be 1.0 for MDI. The scale-angle is undefined for for MDI and will be reported as 0.0. r S_MAJOR SOI scale for semi-major axis of squished image r S_MINOR SOI scale for semi-minor axis of squished image r S_ANGLE SOI position angle of S_MAJOR axis. (degrees) The values for S_MAJOR and S_MINOR will be those to correct the arc-sec per pixel scale, and will thus be near 1.0. These values are given in the coordinate system of the initial image before any of the above implied transformations may have taken place. The S_ANGLE is measured counterclockwise from the +y axis. If these attributes are not present, the default values are 1.0, 1.0, 0.0 respectively. Derived Values The solar radius in pixels will be derived from a number of sources. It can be computed from the IM_SCALE and OBS_DIST parameters, it can be computed from analysis of the current image, or it could be derived from analysis of other contemproary datasets (e.g. the structure program limb data). There will be uncertainty depending on the method used. Programs which need R_SUN will compute it from IM_SCALE and OBS_DIST if it is not present. r R_SUN SOI Apparent radius of sun in pixels. Observable Finally, we should say what we have. The observable quantity will also be reported in a standard way. The following parameters describe that data in a given record. r DATANAME SOI Character string containing observable quantity. r DATAUNIT SOI Character string containing units of DATANAME. r DATASIGN SOI Sign convention. r DATA_MIN SOI Minimum value for data found given record r DATA_MAX SOI Maximum value for data found in given record r DATA_RMS SOI RMS value of data in record r DATAMEAN SOI Mean value of data in record r DATAVALS SOI Number of non-missing values in record For MDI standard names will be used. Examples are 'V', 'I0', 'B', etc. Units for V are m/s, for B are Gauss, for I0 are TBD. There are similar names for the data descriptors applicable to the entire dataset. o D_VARS SOI Number of variables in dataset o DNAMEx SOI Name of variable x o DFNAMEx SOI Filename prefix of variable x o DUNITx SOI Units of variable x o DSIGNx SOI Sign convention of variable x o D_MINx SOI Min value of all recored of variable x o D_MAXx SOI MAx value of all recored of variable x o D_RMSx SOI RMS value of all recored of variable x o DMEANx SOI Mean value of all recored of variable x o DNOTEx SOI Descriptive name of variable x o DVALSx SOI Number of non-missing values in all records of variable x DFNAMEx is a string which along with the record number, can be used to generate the file name for the file containing the variable. This name must be appended to the basename to generate the full file name. The leading "." must be included after the basename if basename is not null. The storage protocol must also be appended based on the PROTOCOL keyword. e.g. if the records are fits files, the name for record 20 for some data, e.g. V_mdi.000019.Vobs.0020.fits would have DFNAME0 of: "Vobs.%04d". The variable counting starts at zero. The DSIGNx parameter describes the sign convention used. It should be present for velocity data where the conventions are: DSIGNx = -1 Astronom Conv, + is redshift -> motion away from obs DSIGNx = 1 post-Copernican view, + is upward on the sun If it is absent, the default must be taken as 1. Conforming Dataset Description o CONFORMS SOI String describing which standard dataset conforms to. Examples are: TS_EQ Equally spaced time series TS Not equally spaced time series o PROTOCOL SOI String describing the storage protocol for the image data file(s) and for the record information file(s) The header protocol is first, followed by the data protocol. Standard file extensions are used, delimited by a ".". Examples are: RDB.FITS .rdb per-record info and fits images FITS.FITS .fits table record-info, fits images RDB.CDF .rdb record info and cdf file with data Reserved by standard protocols ord SIMPLE fits ord NAXIS fits ord END fits d NAXIS1 fits d NAXIS2 fits d BITPIX fits