Here is a sample header. Comments and explanations are in curly brackets {} and refer to the lines below them. The sample header is all in capital letters.
SIMPLE = T / FITS FILE: SKYLAB-ATM-WLCE BITPIX = 16 / 2-BYTE TWOS-COMPL INTEGER NAXIS = 2 / NUMBER OF DIMENSIONS{There are 481 pixels in the horizontal 'x' direction.}
NAXIS1 = 481 / SIZE OF 'X' DIMENSION IN PIXELS{There are usually 480 pixels in the vertical 'y' direction, but this number does vary.}
NAXIS2 = 480 / SIZE OF 'Y' DIMENSION IN PIXELS{This is the date the header and image were created. Day/Month/Year}
DATE = '22/01/96' / DATE HEADER WRITTEN: DD/MM/YY [UT]{These four lines do not change.}
ORIGIN = 'HIGH ALTITUDE OBSERVATORY' INSTRUME= 'SKYLAB-APOLLO TELESCOPE MOUNT' TELESCOP= 'S-052 WHITE LIGHT CORONAGRAPH EXPERIMENT: ATM-WLCE' OBJECT = 'SOLAR CORONA IN WHITE LIGHT (3700-7000 ANGSTROMS)'{The day of year, date, and time of the observation.}
DOY-OBS = '148' / OBSERVATION DOY (DAY OF YEAR) : DDD [UT] DATE-OBS= '28/05/73' / OBSERVATION DATE: DD/MM/YY [UT] TIME-OBS= '18.50.17' / OBSERVATION TIME: HH.MM.SS [UT]{BUNIT tells whether the the data is measured in density or intensity. These imply BSCALE=800.0 or BSCALE=1.e11, respectively.}
BUNIT = 'DENSITY' / DENSITY UNITS BSCALE = 800.0 / PHYSICAL VALUE = BZERO + BSCALE * (ARRAY VALUE){This field always equals 0.00}
BZERO = 0.00 COMMENT THERE IS A STRAY LIGHT FIELD AND VIGNETTING FUNCTION IMPOSED COMMENT BY THE INSTRUMENT ON THE DATA. TO ARRIVE AT TRUE SOLAR COMMENT INTENSITY AND PB, THESE MUST BE REMOVED. HENCE THE COMMENT FOLLOWING PARAMETERS.{These fields are 'Y' (yes) if the function is still in the data, and 'N' (no) if it is not.}
STRAYIN = 'Y' / STRAY LIGHT FIELD IS STILL IN IF 'Y' VIGNETIN= 'Y' / VIGNETTING FUNCTION IS STILL IN IF 'Y' COMMENT BOTH THE STRAY LIGHT FIELD AND VIGNETTING FUNCTION BECOME COMMENT LESS AND LESS RELIABLE BELOW 2.3 SOLAR RADII. THUS COMMENT ********* DATA BELOW 2.3 RSUN ARE UNRELIABLE. ***************{These fields give the exact location of the sun's center.}
CTYPE1 = 'X' / AXIS 1 TYPE: X CRPIX1 = 240.342 / X SUN CENTER [PIXEL] CRVAL1 = 0.00 / X SUN CENTER [ARCSEC] CDELT1 = 24.00 / X COORD INCREMENT [ARCSEC/PIXEL] CTYPE2 = 'Y' / AXIS 2 TYPE: Y CRPIX2 = 248.900 / Y SUN CENTER [PIXEL] CRVAL2 = 0.00 / Y SUN CENTER [ARCSEC] CDELT2 = 24.00 / Y COORD INCREMENT [ARCSEC/PIXEL] **********************************************************************{The film frame number. The first frame, 1, was exposed in May 1973, and the last frame was 35798 from February of 1974.}
FRAME = 61 / FILM FRAME NUMBER{Images can be exposed for 3, 9, or 27 seconds.}
EXPOSURE= 9 / SECONDS THAT FILM WAS EXPOSED{There are four filters.
FILTER = 'CL' / CLEAR FILTER{There were nine camera loads: 1, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B.}
FILMLOAD= '1' / CAMERA FILM LOAD
----------------------------------------------------------------------
COMMENT IMAGE ORIENTATION IS WITH THE PYLON ON THE RIGHT, AND
COMMENT IMAGE ORIGIN IN THE LOWER LEFT.
COMMENT IMAGE ORIGIN IS PIXEL POSITION 0,0
----------------------------------------------------------------------
COMMENT MUCH OF THE WORK DONE ON THE ORIGINAL FILM WAS DONE IN
COMMENT MEASUREMENTS OF MICROMETERS (THE ABBREVIATION MICRONS IS
COMMENT USED BELOW) HENCE THE REFERRAL TO MICRONS IN MANY OF THE
COMMENT MEASUREMENTS BELOW.
COMMENT UNFORTUNATELY, THE MICRON MEASUREMENT SYSTEM WAS DONE WITH
COMMENT THE IMAGE ORIGIN IN THE LOWER *RIGHT* CORNER, AND THE
COMMENT X DIRECTION INCREASING TO THE LEFT, THE REVERSE OF CONVENTION.
COMMENT ALL POSITIONS OF STEP WEDGES, SUN, VIGNETTING, AND STRAY LIGHT
COMMENT CENTERS WERE DONE IN THIS REVERSE X COORDINATE SYSTEM.
COMMENT SO, TO KEEP THINGS UNDERSTANDABLE,
COMMENT ALL PIXEL POSITIONS AND ARCSEC POSITIONS ARE
COMMENT IN "NORMAL" X INCREASING TO THE RIGHT COORDINATES.
COMMENT ALL MICRON POSITIONS ARE GIVEN
COMMENT IN "REVERSE" X INCREASING TO THE LEFT COORDINATES.
COMMENT TO CONVERT FROM MICRONS TO PIXELS:
COMMENT X PIXEL = 480 - (X MICRONS)/50.
COMMENT Y PIXEL = (Y MICRONS)/50.
COMMENT TO CONVERT FROM PIXELS TO MICRONS:
COMMENT X MICRONS = 24000 - (X PIXELS)*50.
COMMENT Y MICRONS = (Y PIXELS)*50.
RSUN-PIX= 40.0 / RADIUS OF THE SUN IN PIXELS
RSUN-MIC= 2000.0 / RADIUS OF THE SUN ON THE FILM IN MICRONS
RSUN-ARC= 960.0 / RADIUS OF THE SUN IN ARC SECONDS
FILM-SCL= 50.0 / MICRONS PER PIXEL ON THE FILM
---------------------------------------------------------------------
COMMENT ON THE IMAGES THERE ARE FOUR FIDUCIAL DOTS. THEY ARE NEAR
COMMENT THE FOUR CORNERS OF THE IMAGE AND APPEAR AS WHITE DOTS
COMMENT IN A STANDARD WHITE TO BLACK COLOR TABLE.
COMMENT AGAIN, IMAGE ORIGIN IS PIXEL POSITION 0,0
FIDUM-LR= '1200,1200' / X,Y POSITION OF LOWER RIGHT FIDUCIAL IN MICRONS
FIDUP-LR= '456,24' / X,Y POSITION OF LOWER RIGHT FIDUCIAL IN PIXELS
FIDUM-LL= '23400,1200' / X,Y POSITION OF LOWER LEFT FIDUCIAL IN MICRONSFIDUP-LL= '12,24' / X,Y POSITION OF LOWER LEFT FIDUCIAL IN PIXELS
FIDUM-UR= '1200,23400' / X,Y POSITION OF UPPER RIGHT FIDUCIAL IN MICRONSFIDUP-UR= '456,468' / X,Y POSITION OF UPPER RIGHT FIDUCIAL IN PIXELS
FIDUM-UL= '23400,23400' / X,Y POSITION OF UPPER LEFT FIDUCIAL IN MICRONSFIDUP-UL= '12,468' / X,Y POSITION OF UPPER LEFT FIDUCIAL IN PIXELS
----------------------------------------------------------------------
COMMENT ROLL IS THE DIRECTION OF SOLAR NORTH W.R.T -Y AXIS IN ARC-MINUTES
COMMENT +ROLL IS IN THE CCW DIRECTION.
COMMENT ROLL= 10800: NORTH AT TOP, EAST ON LEFT, SOUTH AT BOTTOM,
COMMENT WEST UNDER THE PYLON ON THE RIGHT.
COMMENT ROLL= 5400: EAST AT TOP, SOUTH ON LEFT, WEST AT BOTTOM,
COMMENT NORTH UNDER THE PYLON ON THE RIGHT.
COMMENT ROLL= 0: SOUTH AT TOP, WEST ON LEFT, NORTH AT BOTTOM,
COMMENT EAST UNDER THE PYLON ON THE RIGHT.
COMMENT ROLL= -5400: WEST AT TOP, NORTH ON LEFT, EAST AT BOTTOM,
COMMENT SOUTH UNDER THE PYLON ON THE RIGHT.
{Actual value for the spacecraft roll in arc-minutes. It is
the angle, Counter ClockWise (CCW) where **North** is located
with respect to the negative 'Y' axis. }
ROLL = -7372 / DIR OF SOLAR NORTH W.R.T -Y AXIS IN ARC-MINUTES
----------------------------------------------------------------------
COMMENT FINDING SUN CENTER AND THE CENTER OF THE VIGNETTING FUNCTION
COMMENT IS BASED ON PRE-FLIGHT POSITIONS FOR SUN CENTER AND
COMMENT VIGNETTING CENTER. THE PRE-FLIGHT POSITIONS ARE THEN
COMMENT MODIFIED BY POINTING ERRORS AND OFFSETS INTRODUCED BY
COMMENT HOW THE FILM WAS LOADED.
COMMENT THE CENTER OF THE STRAY LIGHT FUNCTION WAS ASSUMED TO BE CONSTANT.
{These are the expected, pre-flight values for the sun, vignetting,
and stray light centers.}
PRESUNX = 12075 / PRE-FLIGHT X SUNCENTER IN MICRONS
PRESUNY = 12479 / PRE-FLIGHT Y SUNCENTER IN MICRONS
PREVIGX = 12234 / PRE-FLIGHT X VIGNETTING CENTER IN MICRONS
PREVIGY = 12440 / PRE-FLIGHT Y VIGNETTING CENTER IN MICRONS
STRYCENX= 12000 / PRE-FLIGHT X STRAY LIGHT CENTER IN MICRONS
STRYCENY= 12000 / PRE-FLIGHT Y STRAY LIGHT CENTER IN MICRONS
----------------------------------------------------------------------
COMMENT PES AND IAS ERRORS ARE POINTING ERRORS.
COMMENT UD REFERS TO UP/DOWN ( Y AXIS )
COMMENT RL REFERS TO RIGHT/LEFT ( X AXIS )
COMMENT IAS IS "INTERNAL ALIGNMENT SENSOR" ERROR AND IS USED FOR
COMMENT QUALITY INFORMATION ONLY.
COMMENT PES IS "POINTING ERROR SENSOR" AND IS USED TO DETERMINE
COMMENT SUN CENTER ON THE FILM FRAME.
COMMENT "SUNOFFDX" AND "SUNOFFDY" ARE OFFSETS THAT ARE CAMERA FILM LOAD
COMMENT SPECIFIC. SEE BELOW.
COMMENT BOTH PES AND IAS WERE SUPPOSED TO BE IN ARCSEC. BUT THE
COMMENT EQUATION FOR SUNCEN BELOW INDICATES THAT THEY ARE NOT.
COMMENT THE UNITS ARE UNCLEAR, BUT THE X DIRECTION SIGN IS TAKEN
COMMENT CARE OF BELOW.
PESUDOK = 17.0 / REASONABLE VALUE FOR PESUD ERROR
PESRLOK = 11.0 / REASONABLE VALUE FOR PESRL ERROR
PESLIM = 5.0 / PES ERRORS ARE OK WITHIN +-PESLIM OF PES..OK
IASUDOK = 0.0 / REASONABLE VALUE FOR IASUD ERROR
IASRLOK = 0.0 / REASONABLE VALUE FOR IASRL ERROR
IASLIM = 10.0 / IAS ERRORS ARE OK WITHIN +-IASLIM OF IAS..OK
PESUD = -7.0 / PES UP-DOWN (Y AXIS) MEASUREMENT
PESRL = -11.0 / PES RIGHT-LEFT (X AXIS) MEASUREMENT
IASUD = -13.0 / IAS UP-DOWN (Y AXIS) MEASUREMENT
IASRL = 10.0 / IAS RIGHT-LEFT (X AXIS) MEASUREMENT
SUNOFFDX= 68.0 / X OFFSET IN CENTER FROM FILM LOADING (MICRONS)
SUNOFFDY= 47.0 / Y OFFSET IN CENTER FROM FILM LOADING (MICRONS)
----------------------------------------------------------------------
COMMENT +++RAW DATA+++ SUN CENTER IS CALCULATED THUSLY:
COMMENT SUNCENX = PRESUNX - SUNOFFDX + 2.19*PESRL (IN MICRONS)
COMMENT SUNCENY = PRESUNY - SUNOFFDY - 1.86*PESUD (IN MICRONS)
SUNCENX = 11982.9 / TRUE SUN CENTER X POSITION IN MICRONS
SUNCENY = 12445.0 / TRUE SUN CENTER Y POSITION IN MICRONS
----------------------------------------------------------------------
COMMENT +++RAW DATA+++ VIGNETTING FUNCTION CENTER IS CALCULATED THUSLY:
COMMENT VIGCENX = PREVIGX - SUNOFFDX (IN MICRONS)
COMMENT VIGCENY = PREVIGY - SUNOFFDY (IN MICRONS)
VIGCENX = 12166.0 / VIGNETTING FUNCTION X CENTER IN MICRONS
VIGCENY = 12393.0 / VIGNETTING FUNCTION Y CENTER IN MICRONS
----------------------------------------------------------------------
{And here's the orientation of an image when the roll is -5400 arc-minutes.
The +'s are the corona, and the 0's are the pylon and other instrument
parts.}
COMMENT SAMPLE OF ROLL= COMMENT -5400 ARC MINUTES WEST COMMENT COMMENT ++ COMMENT ++ COMMENT +++ + COMMENT +++++ COMMENT OOOO OOOOOOOOOOO COMMENT OOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOO COMMENT NORTH OOOOOOOOOO OOOOOOOOOOOOO PYLON SOUTH COMMENT OOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOO COMMENT ^ ++OOOO OOOOOOOOOOO COMMENT ^ + + +++ COMMENT | + + +++ COMMENT | + + ++ COMMENT Y-INCREASING ++ COMMENT + COMMENT 0,0 0,0 COMMENT IN PIXEL COORDINATES EAST IN MICRON COORDINATES COMMENT PIXEL-X INCREASING -----> <----- MICRON-X INCREASING ---------------------------------------------------------------------- COMMENT COMMENT ORIGINAL TAPE.FILE.FRAME.EXPOSUREFILTER.YRDDOY.HHMMSS COMMENT USED IN THE PRODUCTION OF THIS IMAGE ARE AS FOLLOWS: COMMENT XXXXXX.FF.FR00000.00PP.??D???.?????? COMMENT XXXXXX.FF.FR00000.00PP.??D???.?????? COMMENT XXXXXX.FF.FR00000.00PP.??D???.?????? COMMENT XXXXXX.FF.FR00000.00PP.??D???.?????? COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT COMMENT END
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Comments written by: Cathy Andrulis