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KPDC - Continuum Photoheliograms
2k x 2k CCD Full Disk Continuum (Broadband) Photoheliograms at 546 nm (10 nm FWHM)
»go direct to the KPDC synoptic data archives directory...
» Instrument Operations Timeline
» Synoptic Full Disk Continuum Photoheliograms on film - PhoKa (before July 2007)
Data Description - Contents
» Observing Programme
» Coordinate System and Image Orientation
» Data Levels
» Data Processing Pipeline
» Data Formats and File Names
» Daily Synoptic Data Archives Directory Structure"
»Kanzelhöhe Specific FITS Keywords and FITS Sample Headers
more information
» KPDC - Instrument and Data Processing Procedures Description...
Observing Programme
| A. | Patrol of the solar photosphere. Obtain a continuous time series of full disk continuum images whenever weather conditions permit. Instrumental cadence standard is 1 image/min. The cadence in the long term archives may be reduced to 1 image/hour on periods with low or no visible solar activity by selecting the "best image" of that time interval. |
| B. | Publish a representative daily synoptic image of the solar photosphere out of the time series. |
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Coordinate System and Image Orientation
- Coordinate System
- Basically the images are mapped as the solar disk would be seen in the sky with the eye, i. e. N is up, E is to the left. The correction angle Θ specifies the alignment between the x-axis of the image array and the E-W direction. For details about Θ see the » KPDC - Instrument and Data Processing Procedures Description
- Coordinate Origin
- The first pixel in the data array is the left bottom edge of the image.
- Heliographic Coordinates
- P is the position angle of the solar rotation axis (solar N), reckoned positive from (celestial) N towards E.
Data Levels
| A. Raw Level | Data as written by the image acquisition software. Basically all data are in FITS, specific keywords denote properties which have to be recorded at observation time and cannot be restored or recalculated at a later time. A dark current frames (DC) is recorded each day. |
| B. Archive Level | Basically raw data, i. e. the image itself or the pixel data remain unchanged but prepared for archiving and better usability. The processing comprises a quality check of the individual images and a cadence reduction. We avoid any rebinning, averaging or other pixel value manipulation except a) a shifting of the solar disk towards the center coordinates of the field of view (pixel array) by shifting an integer number of pixels and b) setting pixels far outside the solar disk to 0 for a better compression of the data. More keywords are inserted into the FITS headers to make the data compliant with common accepted data standards. |
| C. Synoptic Level | A gain table correction (flatfield) which assumes circular symmetry on large scales on the solar disk ("Burlov"-method) is applied to archive level data. This method delivers also a center to limb variation (CLV) profile and therefore a "quiet Sun map". Dividing the flatfielded image by this "quiet Sun map" yields a normalized ("flat") solar disk image where the quiet sun level corresponds to 1 in the data array. In particular for the JPEG copies the contrast is enhanced by unsharp masking and a linear rescaling of the actual intensity range (e.g. 0...120% of the int. at disk center) to full byte scale (0...255), for individual properties of the data products see the formats and the data processing pipeline section.
The daily synoptic image is processed according to this level and published in various formats. |
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Data Processing Pipeline
The data processing pipeline describes the work flow from the data acqusition to the final data repository in the archives and substantial processing steps.
At Observation Time |
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| -- expose to constant "density" | vary exposure time to adapt for equal average intensities in AOI in each frame |
| -- frame selection on pixel contrast | calculate standard deviation of intensities in AOI and select frame with max. std. dev. within a certain number of frames |
| --» A. Raw Level Data | FITS, normally not available |
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After Observation Processing |
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| -- discard corrupted images | check for reasonable disk radii and intensities in all quadrants |
| -- cadence reduction | select "best of hour" by the Optimum Window Method, or keep all during high activity periods |
| -- determination of actual disk center coord. and radii | |
| -- shift disk to center of FoV | only by integer number of pixel to avoid any data averaging |
| -- calculate properties and parameters for achive level data | e. g. angle Θ, image scale,... |
| -- mask outside disk = 0 | set pixels far outside the disk to zero for a better data compression |
| --» B. Archive Level Data | FITS, optional JPEG available |
| -- application of a gain table (flatfield) | "Burlov"-method, which assumes and reduces the image to a circular symmetry on large scales and delivers also a CLV profile |
| -- calculate properties and parameters for synoptic level data | e. g. P, B0, L0 and SOHO standard FITS keys for synoptic observations |
| -- contrast enhancement and derotation | unsharp masking, intensity range rescaling, rotated by P and Θ to have solar N up |
| --» C1 Synoptic Level Data | denominated as "low contrast", FITS and JPEG available. |
| -- normalization | divide by CLV (quiet Sun map) |
| -- contrast enhancement and derotation | unsharp masking, linear intensity range rescaling, rotated by P and Θ to have solar N up |
| --» C2 Synoptic Level Data - normalized | denominated as "high contrast", FITS and JPEG available. |
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Optimum Window Method (see Giammanco, 2000, Astron. Astrophys. Suppl. Ser. 147, 1)
Data Formats and File Names
| File | Explanation |
| A. Raw Level Data |
wlYYYYMMDD_hhmmss.fts.gz
| raw level image frame, 2 Byte integer, compressed FITS |
dcYYYYMMDD_hhmmss.fts.gz
| raw level dark current frame, 2 Byte integer, compressed FITS |
YYYYMMDD.NAM
| list of available raw level images which passed the quality checking and cadence reduction procedure of the corresponding date, ASCII text |
| B. Archive Level Data |
YYYYMMDD_hhmmss.fts.gz
| archive level image frame, 2 Byte integer, compressed FITS |
YYYYMMDD_hhmmss.jpg
| archive level image frame, half scale, JPEG |
| C. Synoptic Level Data |
kanz_bband_fd_YYYYMMDD_hhmm.ar.fts.gz
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archive level representation of the daily synoptic image, 2 Byte integer, compressed FITS |
kanz_bband_fd_YYYYMMDD_hhmm.clv.fts.gz
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center to limb variation (CLV) profile, derived by the flatfielding procedure, compressed FITS ASCII table |
kanz_bband_fd_YYYYMMDD_hhmm.hi.fts.gz
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normalized image (CLV contrast compensated), rescaled to by use of BSCALE=0.01 to 1 Byte integer, compressed FITS |
kanz_bband_fd_YYYYMMDD_hhmm.hi.jpg
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normalized image (CLV contrast compensated), unsharp masking, intensity rescaling 40...120% -> 0...255, derotated for P and angle Θ, heliograph. coordinate grid, half scale, JPEG |
kanz_bband_fd_YYYYMMDD_hhmm.lo.fts.gz
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gain table corrected image, 2 Byte integer, compressed FITS |
kanz_bband_fd_YYYYMMDD_hhmm.lo.jpg
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gain table corrected image, unsharp masking, intensity rescaling 0...120% -> 0...255, derotated for P and angle Θ, half scale, JPEG |
YYYYMMDD_hhmm[ss]...date and time of the observation, daily synoptic files may appear without seconds [ss] in filename
The file names comply with the SOHO
file name convention for synoptic data.
Daily Synoptic Data Archives Directory Structure (rel. to web-root)
»go to the KPDC synoptic data archives directory...
YYYY... subdirectory according to the year of observation
Kanzelhöhe Specific FITS Keywords and FITS Sample Headers
In the list below there are explanations of Kanzelhöhe specific FITS keywords and essential hints for the interpretation of FITS standard keywords, some other keywords might be self explaining. The FITS data files comply fully with the FITS standard and make use of the proposed keywords for SOHO. Please refer to these documentations for a comprehensive explanation of standard or SOHO specific keywords.
» FITS standard
» Proposed keywords for SOHO
Explanations
- coordinate system
- pixel 0,0...left, bottom
- NAXIS1
- CCD x-axis, roughly parallel to E-W
- NAXIS2
- CCD y-axis, roughly parallel to N-S
- CTYPE1, CTYPE2
- description of the physical meaning of the coordinate axes
- CRPIX1, CRPIX2
- position of physical coordinate origin within the data array, here position of the solar disk center
(standard FITS keyword)
- CRVAL1, CRVAL2
- optional offsets of the origin defined by CRPIX1, CRPIX2
- CDELT1, CDELT2
- scale of the physical units per pixel [arcsec/px]
- CENTER_X, CENTER_Y
- position of solar disk center in coordinates of the data array
- SOLAR_R
- actual solar radius in pixels
- ANGLE
- derotation angle P + Θ: rotate the image by ANGLE to have the solar rotational axis parallel to NAXIS2 (solar N up)
- SOLAR_P0, SOLAR_B0
- actual physical ephemeris P and B0 at the time of observation
- pixel values
- ADU = BZERO + BSCALE * D,
ADU...intensity level at the CCD in data units (for a 10 bit Cam from 0...1023),
D...value (as a 2 byte integer) of the corresponding array element in the FITS data array
- DATAMIN, DATAMAX
- min and max of of the CCD pixel values in data units (ADUs)
- descriptive
- observing conditions and data processing
- EXP_TIME
- actual exposure (integration) time used for the frame either in msec or sec
- EXP_MODE
- exposure mode:
0...exposure time is controlled by the image acquisition application to reach a preselected level (PRE_INT) of pixel values in the area of interest (a rectangle defined by A_O_INT),
1...the actual expsoure time is twice the value which is needed to reach the PRE_INT level,
2...the actual exposure time is fixed to the value given by EXP_TIME,
3...combination of 1 and 2
- PRE_INT
- preselected level (mean of pixel values in the area of interest) which should be reached by adapting the integration time
- A_O_INT
- the vector defines the area of interest (AOI) in pixel coordinates. The AOI is used for the calculation of a mean value and a standard deviation needed of exposure time control and frame selection
- TYPE-DP
- data processing level:
raw...raw data level
archive...archive data level
low...synoptic data level, normal contrast
high...synoptic data level, normalized (CLV compensated)
- TELESCOP
- telescope used for observation, original string 'KANZELHOEHE PHOTOSPHERE TELESCOPE' was changed to 'KPT'
- ORIGIN
- observing programme which created the observations
Reading und Understanding the CLV Profile from the FITS ASCII Data Tables
The CLV profile is saved as a ACSII data table which is defined in an extension of the FITS header (see section D.). The meaning of the standard keywords is a little bit different as for image data. The 42 characters of each line form 3 columns of E14.7 format numbers written digit behind digit, TBCOLi gives the starting column of the i-th number of the line. There are 2045 lines of data representing the steps for the profile calculation from solar disk center towards the limb and beyond. The first number of each line gives the distance r from disk center in units of solar radii, the second the same distance measured in μ (μ2 = 1-r2), and the third the calculated intensity level of a quiet sun in data units (ADUs) at that position.
A. Raw Level Data: FITS Sample Header
SIMPLE = T / file does conform to FITS standard
BITPIX = 16 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 2048 / length of data axis 1
NAXIS2 = 2048 / length of data axis 2
BZERO = 32768 / offset data range to that of unsigned short
BSCALE = 1 / default scaling factor
DATE_OBS= '2007-11-12T10:30:24Z' / Date of observation
EXP_TIME= 5.886 / Exposure Time [ms]
EXP_MODE= 0 / Exp. Mode (0=auto,1=dbl,2=fix,3=both)
PRE_INT = 850 / Preselected PixInt in AOI
A_O_INT = '900,1000,1100,1009' / Rect. for PixInt [X0,Y0,X1,Y1]
OBJECT = 'SUN ' / NOAA # or SUN for full disk
OBSTYPE = 'BBAND '
TYPE-DP = 'RAW ' / Data Processing Type
TELESCOP= 'KANZELHOEHE PHOTOSPHERE TELESCOPE'
INSTRUME= 'TM4100 ' / Camera Type
ORIGIN = 'KANZELHOEHE PHOTOSPHERE PATROL'
HISTORY Raw data from aquisition software, no processing applied
COMMENT coord-origin: left bottom
COMMENT Kanzelhoehe Observatory, A-9521 Treffen
COMMENT Univ. of Graz, Austria
END
B. Archive Level Data: FITS Sample Header
SIMPLE = T
BITPIX = 16
NAXIS = 2
NAXIS1 = 2048
NAXIS2 = 2048
BUNIT = 'CCD COUNTS'
BSCALE = 1.00000
BZERO = 32768.0
DATAMIN = 0
DATAMAX = 957
CTYPE1 = 'SOLAR X ' / [arcsec/px]
CTYPE2 = 'SOLAR_Y ' / [arcsec/px]
CRPIX1 = 1025.22
CRPIX2 = 1025.31
CRVAL1 = 0.00000
CRVAL2 = 0.00000
CDELT1 = 1.02376
CDELT2 = 1.02376
DATE_OBS= '2007-11-21T08:09:23Z'
CENTER_X= 1025.22 / [pix]
CENTER_Y= 1025.31 / [pix]
SOLAR_R = 948.802 / [pix]
ANGLE = 18.8725 / [deg]
SOLAR_P0= 19.6450 / [deg]
SOLAR_B0= 2.14354 / [deg]
OBJECT = 'SUN '
TYPE-DP = 'ARCHIVE ' / Data Processing Type
OBS_TYPE= 'BBAND '
TELESCOP= 'KPT '
INSTRUME= 'TM4100 '
WAVELNTH= 5460 / [ANG], FWHM=100 [ANG]
EXPTIME = 0.0143880 / [sec]
EXP_MODE= 0 / Exp. Mode (0=auto,1=dbl,2=fix,3=both)
PRE_INT = 850 / Preselected PixInt in AOI
A_O_INT = '900,1000,1100,1009' / Rect. for PixInt [X0,Y0,X1,Y1]
ORIGIN = 'KANZELHOEHE PHOTOSPHERE PATROL'
DATE = '2007-11-21' / Date of FITS Creation
COMMENT Orientation: N up, W right, first pix is left bottom
COMMENT Pixels far outside disk are set to 0
COMMENT KANZELHOEHE SOLAR OBSERVATORY
COMMENT A-9521 TREFFEN, AUSTRIA
END
C. Synoptic Level Data: FITS Sample Header
SIMPLE = T
BITPIX = 16
NAXIS = 2
NAXIS1 = 2048
NAXIS2 = 2048
BUNIT = 'CCD COUNTS'
BSCALE = 1.00000
BZERO = 32768.0
DATAMIN = 0
DATAMAX = 902
CTYPE1 = 'SOLAR X ' / [arcsec/px]
CTYPE2 = 'SOLAR_Y ' / [arcsec/px]
CRPIX1 = 1025.76
CRPIX2 = 1025.26
CRVAL1 = 0.00000
CRVAL2 = 0.00000
CDELT1 = 1.02324
CDELT2 = 1.02324
DATE_OBS= '2007-11-21T07:58:16Z'
CENTER_X= 1025.76 / [pix]
CENTER_Y= 1025.26 / [pix]
SOLAR_R = 949.285 / [pix]
ANGLE = 22.8817 / [deg]
SOLAR_P0= 19.6474 / [deg]
SOLAR_B0= 2.14447 / [deg]
OBJECT = 'SUN '
TYPE-DP = 'LOW ' / Data Processing Type
OBS_TYPE= 'BBAND '
TELESCOP= 'KPT '
INSTRUME= 'TM4100 '
WAVELNTH= 5460 / [ANG], FWHM=100 [ANG]
EXPTIME = 0.0113370 / [sec]
ORIGIN = 'KANZELHOEHE PHOTOSPHERE PATROL'
DATE = '2007-11-21' / Date of FITS Creation
HISTORY Large scale asymmetries corrected by fitting
HISTORY polynomials into rings of the Solar disk
COMMENT Orientation: N up, W right, first pix is left bottom
COMMENT KANZELHOEHE SOLAR OBSERVATORY
COMMENT A-9521 TREFFEN, AUSTRIA
END
D. Synoptic Level Data: FITS Sample Extension Header for CLV Data Tables
XTENSION= 'TABLE '
BITPIX = 8
NAXIS = 2
NAXIS1 = 42
NAXIS2 = 2045
PCOUNT = 0
GCOUNT = 1
TFIELDS = 3
TBCOL1 = 1
TFORM1 = 'E14.7 '
TBCOL2 = 15
TFORM2 = 'E14.7 '
TBCOL3 = 29
TFORM3 = 'E14.7 '
BUNIT1 = 'FRACS OF DISK'
BUNIT2 = '1-R*R '
BUNIT3 = 'CCD COUNTS'
TTYPE1 = 'RADIUS '
TTYPE2 = 'MIU '
TTYPE3 = 'CLVSA_R '
END
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