Section 7. Wide Field/Planetary Camera 2
Observation datasets produced by the Wide Field/Planetary Camera 2 u (WFPC 2) are calibrated by the calwp2 task. This task requires a set of reference files to perform the calibration, as described in this section.
All reference files for the WFPC 2 calibration must be in GEIS format. All files must contain four groups of two-dimensional data. The groups correspond to the CCD detectors in the WFPC 2 camera in the nominal readout order. That is, group 1 contains the image from CCD PC1, group 2 contains the image from CCD WFC2, group 3 contains the image from CCD WFC3, and group 4 contains the image from CCD WFC4. The keyword DETECTOR in the group parameter block should agree with this convention. The data is of either 2-byte integer (INTEGER*2) or singleprecision real (REAL*4) data type.
Reference file headers must be copies of the headers created during generic conversion for the WFPC 2 science image (*. D0H) file. This is to ensure a common header format throughout the WFPC 2 calibration process. This header format will be known as the WFPC 2 generic header. Additional keywords (especially comment and history keywords) may be appended to the headers. However, the size of the group parameter block should not be changed.
7.1 Data Quality Files
Most WFPC 2 reference files are accompanied by a data quality file (DQF) that flags unsatisfactory pixel values. This information is propagated in the output DQF produced by calwp2. The DQFs are all of short integer (INTEGER*2) data type, have the same number of dimensions as the files associated with them, and have headers in the same format as the WFPC 2 generic header.
By convention, DQF pixel values of 0 designate good pixels. The values of the DQFs of all images used in the processing are bitwise ORed together. Generic calibration defects are flagged with the value 2. Table 7-1 shows the DQF condition codes used in routine WFPC 2 pipeline processing.
Table 7-1. WFPC 2 Data Quality Flag Values
Condition |
Value |
Comment |
|---|---|---|
GOODPIXEL |
0 |
Unflagged pixel |
SOFTERROR |
1 |
R-S error in data transmission |
CALIBDEFECT |
2 |
Generic problem with reference file |
STATICDEFECT |
4 |
Static defect in WFPC 2 camera |
ATODSAT |
8 |
A-to-D converter was saturated - value unknown |
DATALOST |
16 |
Missing data BADPIXEL 32 Generic bad pixel - reason not specified |
OVERLAP |
64 |
Portion of image not corrected for aberration |
NOTUSED |
128 |
Flag value not used |
CTTRAPCOL |
256 |
Column above charge transfer trap |
UNFIXHOTPIX |
512 |
Highly variable hot pixel, cannot be fixed |
FIXABLEHOTPIX |
1024 |
Moderate hot pixel (fix via warmpix task) |
7.2 WFPC 2 Reference Files
WFPC 2 reference files are composed of a FITS header file and a binary data file. Although the header files do follow the FITS conventions, the header listings in this section do not adhere precisely to these conventions.
In the header listings contained in this section, beware of the following:
The single quotes required around character strings have been omitted.
Numerical values have not been right justified.
The third column in the listing denoting the variable type is additional information, not part of the FITS header itself.
All WFPC 2 reference files have image headers that contain the same keywords as shown in the following header listing. For the descriptions of the individual reference files only a partial header listing is given to show which keywords are essential and are likely to change from one reference file to another.
The following reference files are used for calibrating WFPC 2 observations:
Static Mask: Formerly known as the data quality mask, this file flags those pixels that always contain degraded values (e.g., blocked columns, hot pixels). This mask is routinely incorporated into the DQF generated in the RSDP pipeline by calwp2 (the .C1H file).
A-to-D Lookup Tables: These files are used to correct the image data for a pattern introduced by the analog-to-digital converter electronics. This correction replaces the short integer pixel values obtained from the WFPC 2 with floating-point values that remove the systematic degradation introduced by this hardware problem.
Bias Reference File and DQF: These files are subtracted from the image to remove the structure in the electronic bias.
Dark Reference File and DQF: The WFPC 2 CCDs generate a spurious signal during exposures known as dark current. This signal is a function of the time since the last erase command and the operating temperature of the CCD detectors and varies from pixel to pixel. The dark reference file is scaled by the time since the last erase command and subtracted from the image.
Flat Field Reference File and DQF: Variations in sensitivity between pixels in the CCD detectors are corrected by applying a flat field reference file. This file contains the normalized inverse sensitivity (gain) for each pixel in the detector. It is made from internal exposures in conjunction with streaked earth flats. The image is multiplied by the flat field file after correction for additive effects (i.e., bias and dark).
Shutter Shading Reference File: When a WFPC 2 exposure is relatively short, shutter shading (resulting from the finite time of flight of the shutter blade) gives rise to uneven illumination across the field of view. This is corrected by means of an additive correction that varies spatially according to the shutter shading reference file, which is scaled for the appropriate exposure time.
7.2.1 Generic Image Header: All WFPC 2 Reference Files
The following listing shows a standard header used by all WFPC 2 reference files.
Instrument: WIDEFIELD PLANETARY CAMERA II Revised: 20-AUG-93 File Type: SCIENCE DATA HEADER
SIMPLE = F data conforms to the fits standard L1
BITPIX = 16 bits per data value I2
DATATYPE= INTEGER*2 datatype of the group array C10
NAXIS = 2 number of data axes I2
NAXIS1 = length of 1st data axis I2
NAXIS2 = length of 2nd data axis I2
GROUPS = T data has groups L1
GCOUNT = 1 number of groups per observation (1-4) I2
PCOUNT = 38 number of parameters I2
PSIZE = 1760 bits in each parameter block I2
/ GROUP PARAMETERS: OSS
PTYPE1 = CRVAL1 right ascension of reference pixel (deg) C08
PDTYPE1 = REAL*8 C18
PSIZE1 = 64 I2
PTYPE2 = CRVAL2 declination of reference pixel (deg) C08
PDTYPE2 = REAL*8 C18
PSIZE2 = 64 I2
PTYPE3 = CRPIX1 x-coordinate of reference pixel C08
PDTYPE3 = REAL*4 C18
PSIZE3 = 32 I2
PTYPE4 = CRPIX2 y-coordinate of reference pixel C08
PDTYPE4 = REAL*4 C18
PSIZE4 = 32 I2
PTYPE5 = CD1_1 partial of the right ascension w.r.t. x C08
PDTYPE5 = REAL*4 C18
PSIZE5 = 32 I2
PTYPE6 = CD1_2 partial of the right ascension w.r.t. y C08
PDTYPE6 = REAL*4 C18
PSIZE6 = 32 I2
PTYPE7 = CD2_1 partial of the declination w.r.t. x C08
PDTYPE7 = REAL*4 C18
PSIZE7 = 32 I2
PTYPE8 = CD2_2 partial of the declination w.r.t. y C08
PDTYPE8 = REAL*4 C18
PSIZE8 = 32 I2
PTYPE9 = DATAMIN minimum value of the data C08
PDTYPE9 = REAL*4 C18
PSIZE9 = 32 I2
PTYPE10 = DATAMAX maximum value of the data C08
PDTYPE10= REAL*4 C18
PSIZE10 = 32 I2
PTYPE11 = MIR_REVR is the image mirror reversed? C08
PDTYPE11= LOGICAL*4 C18
PSIZE11 = 32 I2
PTYPE12 = ORIENTAT orientation of the image (deg) C08
PDTYPE12= REAL*4 C18
PSIZE12 = 32 I2
PTYPE13 = FILLCNT number of segments containing fill C08
PDTYPE13= INTEGER*4 C18
PSIZE13 = 32 I2
PTYPE14 = ERRCNT number of segments containing errors C08
PDTYPE14= INTEGER*4 C18
PSIZE14 = 32 I2
PTYPE15 = FPKTTIME time of the first packet C08
PDTYPE15= REAL*8 (Modified Julian Date) C18
PSIZE15 = 64 I2
PTYPE16 = LPKTTIME time of the last packet C08
PDTYPE16= REAL*8 (Modified Julian Date) C18
PSIZE16 = 64 I2
PTYPE17 = CTYPE1 first coordinate type C08
PDTYPE17= CHARACTER*8 C18
PSIZE17 = 64 I2
PTYPE18 = CTYPE2 second coordinate type C08
PDTYPE18= CHARACTER*8 C18
PSIZE18 = 64 I2
PTYPE19 = DETECTOR CCD detector: PC 1, WFC 2-4 C08
PDTYPE19= INTEGER*4 C18
PSIZE19 = 32 I2
/ GROUP PARAMETERS: PODPS
PTYPE20 = DEZERO mean bias level from EED extended register C08
PDTYPE20= REAL*4 C18
PSIZE20 = 32 I2
PTYPE21 = BIASEVEN bias level for even-numbered columns C08
PDTYPE21= REAL*4 C18
PSIZE21 = 32 I2
PTYPE22 = BIASODD bias level for odd-numbered columns C08
PDTYPE22= REAL*4 C18
PSIZE22 = 32 I2
PTYPE23 = GOODMIN minimum value of the "good" pixels C08
PDTYPE23= REAL*4 C18
PSIZE23 = 32 I2
PTYPE24 = GOODMAX maximum value of the "good" pixels C08
PDTYPE24= REAL*4 C18
PSIZE24 = 32 I2
PTYPE25 = DATAMEAN mean value of the "good" pixels C08
PDTYPE25= REAL*4 C18
PSIZE25 = 32 I2
/ GROUP PARAMETERS: DATA QUALITY FILE SUMMARY
PTYPE26 = GPIXELS number of "good" pixels (DQF=0) C08
PDTYPE26= INTEGER*4 C18
PSIZE26 = 32 I2
PTYPE27 = SOFTERRS number of "soft error" pixels (DQF=1) C08
PDTYPE27= INTEGER*4 C18
PSIZE27 = 32 I2
PTYPE28 = CALIBDEF number of "calibration defect" pixels (DQF=2) C08
PDTYPE28= INTEGER*4 C18
PSIZE28 = 32 I2
PTYPE29 = STATICD number of "static defect" pixels (DQF=4) C08
PDTYPE29= INTEGER*4 C18
PSIZE29 = 32 I2
PTYPE30 = ATODSAT number of "A to D saturated" pixels (DQF=8) C08
PDTYPE30= INTEGER*4 C18
PSIZE30 = 32 I2
PTYPE31 = DATALOST number of "data lost" pixels (DQF=16) C08
PDTYPE31= INTEGER*4 C18
PSIZE31 = 32 I2
PTYPE32 = BADPIXEL number of "generic bad" pixels (DQF=32) C08
PDTYPE32= INTEGER*4 C18
PSIZE32 = 32 I2
PTYPE33 = OVERLAP number of "image overlap" pixels (DQF=64) C08
PDTYPE33= INTEGER*4 C18
PSIZE33 = 32 I2
/ GROUP PARAMETERS: PHOTOMETRY
PTYPE34 = PHOTMODE photometry mode C08
PDTYPE34= CHARACTER*48 C18
PSIZE34 = 384 I2
PTYPE35 = PHOTFLAM inverse sensitivity C08
PDTYPE35= REAL*4 C18
PSIZE35 = 32 I2
PTYPE36 = PHOTZPT zero point C08
PDTYPE36= REAL*4 C18
PSIZE36 = 32 I2
PTYPE37 = PHOTPLAM pivot wavelength C08
PDTYPE37= REAL*4 C18
PSIZE37 = 32 I2
PTYPE38 = PHOTBW RMS bandwidth of the filter C08
PDTYPE38= REAL*4 C18
PSIZE38 = 32 I2
/ WFPC-II DATA DESCRIPTOR KEYWORDS
INSTRUME= WFPC2 instrument in use C06
ROOTNAME= rootname of the observation set C12
FILETYPE= SCI shp, ext, edq, sdq, sci C03
/ SCIENCE INSTRUMENT CONFIGURATION
MODE = instr. mode: FULL (full res.), AREA (area int.) C04
SERIALS = serial clocks: ON, OFF C03
/ IMAGE TYPE CHARACTERISTICS
IMAGETYP= EXT DARK/BIAS/IFLAT/UFLAT/VFLAT/KSPOT/EXT/ECAL C18
CDBSFILE= NO GENERIC/BIAS/DARK/FLAT/MASK/ATOD/SHAD/NO C18
PKTFMT = packet format code I4
DATE = date file written (dd/mm/yy) C08
/ FILTER CONFIGURATION
FILTNAM1= first filter name C08
FILTNAM2= second filter name C08
FILTER1 = first filter number (0-48) I2
FILTER2 = second filter number (0-48) I2
FILTROT = partial filter rotation angle (degrees) R4
LRFWAVE = linear ramp filter wavelength R4
/ INSTRUMENT STATUS USED IN DATA PROCESSING
UCH1CJTM= TEC cold junction #1 temperature (Celsius) R4
UCH2CJTM= TEC cold junction #2 temperature (Celsius) R4
UCH3CJTM= TEC cold junction #3 temperature (Celsius) R4
UCH4CJTM= TEC cold junction #4 temperature (Celsius) R4
UBAY3TMP= Bay 3 A1 temperature (deg C) R4
KSPOTS = status of Kelsall spot lamps: ON, OFF C03
SHUTTER = shutter in place during IFLAT (A or B) C01
ATODGAIN= analog to digital gain (Electrons/DN) R4
/ RSDP CONTROL KEYWORDS
MASKCORR= PERFORM do mask correction: PERFORM, OMIT, COMPLETE C08
ATODCORR= do A-to-D correction: PERFORM, OMIT, COMPLETE C08
BLEVCORR= do bias level correction: PERFORM, OMIT, COMPLET C08
BIASCORR= do bias correction: PERFORM, OMIT, COMPLETE C08
DARKCORR= do dark correction: PERFORM, OMIT, COMPLETE C08
FLATCORR= do flat field correction: PERFORM, OMIT, COMPLETE C08
SHADCORR= do shaded shutter correction: PERFORM, OMIT, COMPLETE C08
DOSATMAP= OMIT output saturated pixel map: PERFORM, OMIT, COMPLETE C08
DOPHOTOM= fill photometry keywords: PERFORM, OMIT, COMPLETE C08
DOHISTOS= OMIT make histograms: PERFORM, OMIT, COMPLETE C08
OUTDTYPE= REAL output image datatype: REAL, LONG, SHORT C06
/ CALIBRATION REFERENCE FILES
MASKFILE= name of the input DQF of known bad pixels C18
ATODFILE= name of the A-to-D conversion file C18
BLEVFILE= engineering file with extended register data C18
BLEVDFIL= engineering file DQF C18
BIASFILE= name of the bias frame reference file C18
BIASDFIL= name of the bias frame reference DQF C18
DARKFILE= name of the dark reference file C18
DARKDFIL= name of the dark reference DQF C18
FLATFILE= name of the flat field reference file C18
FLATDFIL= name of the flat field reference DQF C18
SHADFILE= name of the reference file for shutter shading C18
PHOTTAB = name of the photometry calibration table C18
GRAPHTAB= the HST graph table C18
COMPTAB = the HST components table C18
/ DEFAULT KEYWORDS SET BY STSCI
SATURATE= 4095 data value at which saturation occurs I2
USCALE = 1.0 scale factor for output image R4
UZERO = 0.0 zero point for output image R4
/ READOUT DURATION INFORMATION
READTIME= Length of time for CCD readout in clock ticks I4
/ PLANETARY SCIENCE KEYWORDS
PA_V3 = 0.0 position angle of v3 axis of HST R4
RA_SUN = 0.0 right ascension of the sun (deg) R8
DEC_SUN = 0.0 declination of the sun (deg) R8
EQNX_SUN= 2000.0 equinox of the sun R4
MTFLAG = F moving target flag L1
EQRADTRG= 0.0 equatorial radius of target R4
FLATNTRG= 0.0 flattening of target R4
NPDECTRG= 0.0 north pole declination of target R4
NPRATRG = 0.0 north pole right ascension of target R4
ROTRTTRG= 0.0 rotation rate of target R4
LONGPMER= 0.0 longitude of prime meridian R4
EPLONGPM= 0.0 epoch of longitude of prime meridian R4
SURFLATD= 0.0 surface feature latitude R4
SURFLONG= 0.0 surface feature longitude R4
SURFALTD= 0.0 surface feature altitude R4
/ PODPS FILL VALUES
PODPSFF = 0=(no PODPS fill), 1=(PODPS fill present) I2
STDCFFF = 0=(no ST DCF fill), 1=(ST DCF fill present) I2
STDCFFP = ST DCF fill pattern (hex) C04
RSDPFILL= -100 bad data fill value for calibrated images I2
/ EXPOSURE TIME AND RELATED INFORMATION
UEXPODUR= commanded duration of exposure (seconds) I4
NSHUTA17= number of AP17 shutter B closes I4
DARKTIME= dark time (seconds) R4
UEXPOTIM= major frame pulse time preceding exposure start I4
PSTRTIME= predicted obs. start time (yyyy:ddd:hh:mm:ss) C18
PSTPTIME= predicted obs. stop time (yyyy:ddd:hh:mm:ss) C18
/ EXPOSURE INFORMATION
EQUINOX = J2000 equinox of the celestial coordinate system C08
SUNANGLE= angle between sun and V1 axis (deg) R4
MOONANGL= angle between moon and V1 axis (deg) R4
SUN_ALT = altitude of the sun above Earth's limb (deg) R4
FGSLOCK = commanded FGS lock (FINE,COARSE,GYROS,UNKNOWN) C07
DATE-OBS= UT date of start of observation (dd/mm/yy) C08
TIME-OBS= UT time of start of observation (hh:mm:ss) C08
EXPSTART= exposure start time (Modified Julian Date) R8
EXPEND = exposure end time (Modified Julian Date) R8
EXPTIME = exposure duration (seconds)--calculated R4
EXPFLAG = exposure interruption indicator C13
/ TARGET & PROPOSAL ID
TARGNAME= proposer's target name C30
RA_TARG = right ascension of the target (deg) (J2000) R8
DEC_TARG= declination of the target (deg) (J2000) R8
PROPOSID= PEP proposal identifier I4
PEP_EXPO= PEP exposure identifier including sequence C15
LINENUM = PEP proposal line number C15
SEQLINE = PEP line number of defined sequence C15
SEQNAME = PEP define/use sequence name C15
END
7.2.2 Static Bad Pixel Mask Files (MSK): <uniquename>.R0H
The static mask files (formerly known as the data quality masks) contain flags for those pixels that always contain degraded values. This mask is routinely incorporated into the data quality file generated in the RSDP pipeline by calwp2.
Format: The static mask file is a short integer (INTEGER*2) image file of four groups with the same dimensions as the WFPC 2 science image. The image contains values of 0 in all pixels, except for those with known static defects. Defective pixels are flagged with the value 4.
Flags and Indicators: The flag and indicator used to select the static mask reference files is MODE (which can be either AREA or FULL).
Restrictions: The static mask reference file is not accompanied by a data quality file. The header of the static mask image is a copy of the WFPC 2 science data header.
The following listing shows a sample WFPC 2 static mask reference file.
BITPIX = 16 / bits per data value I2
DATATYPE= INTEGER*2 / data type of the array C10
PTYPE9 = DATAMIN / minimum value of the data C08
PDTYPE9 = REAL*4 C18
PSIZE9 = 32 I2
PTYPE10 = DATAMAX / maximum value of the data C08
PDTYPE10= REAL*4 C18
PSIZE10 = 32 I2
PTYPE19 = DETECTOR / CCD detector: PC 1, WFC 2-4 C08
PDTYPE19= INTEGER*4 C18
PSIZE19 = 32 I2
PTYPE23 = GOODMIN / minimum value of the "good" pixels C08
PDTYPE23= REAL*4 C18
PSIZE23 = 32 I2
PTYPE24 = GOODMAX / maximum value of the "good" pixels C08
PDTYPE24= REAL*4 C18
PSIZE24 = 32 I2
PTYPE25 = DATAMEAN / mean value of the "good" pixels C08
PDTYPE25= REAL*4 C18
PSIZE25 = 32 I2
PTYPE26 = GPIXELS / number of "good" pixels (DQF=0) C08
PDTYPE26= INTEGER*4 C18
PSIZE26 = 32 I2
PTYPE28 = CALIBDEF / number of "calibration defect" pixels (DQF=2) C08
PDTYPE28= INTEGER*4 C18
PSIZE28 = 32 I2
PTYPE29 = STATICD / number of "static defect" pixels (DQF=4) C08
PDTYPE29= INTEGER*4 C18
PSIZE29 = 32 I2
INSTRUME= WFII / instrument in use C04
ROOTNAME= / rootname of the observation set C12
FILETYPE= MSK / file type: msk, bas, drk, flt C03
MODE = / instr. mode: FULL (full res.), AREA (area int.) C04
SERIALS = / serial clocks: ON, OFF C03
IMAGETYP= SPECIAL / image type: EXT/BIAS/DARK/IFLAT/UFLAT/VFLAT/ECAL C18
CDBSFILE= MASK / CDBS: YES/NO/BIAS/DARK/FLAT/MASK/ATOD/SHAD C18
DATE = / date file written (dd/mm/yy) C08
FILTNAM1= / first filter name C08
FILTNAM2= / second filter name C08
FILTER1 = / first filter number (0-48) I2
FILTER2 = / second filter number (0-48) I2
SHUTTER = / shutter in place during IFLAT (A or B) C01
ATODGAIN= / analog to digital gain (Electrons/DN) R4
EXPTIME = / exposure duration (seconds) -- calculate R4
TARGNAME= / target name C30 END [Listing Version 01 09-JUL-1992]
7.2.3 A-to-D Lookup Table Files (A2D): <uniquename>.R1H
The A-to-D lookup table files are used to correct the image data for a pattern introduced by the analog-to-digital converter electronics. This is done by replacing the short integer pixel values obtained from the WFPC 2 with floating-point values that remove the systematic degradation introduced by this hardware problem.
Format: The A-to-D lookup table file is a single-precision (REAL*4) image file with a line length (NAXIS1) of 4096 and multiple lines. The first line contains a value of -1 in pixel 1 and the Bay 3 temperature (in degrees Kelvin) for each A-to-D lookup table in subsequent pixels.
The index of these pixels must correspond to the line containing that lookup table. The remainder of the first line is filled with -1 values.
Flags and Indicators: The flag and indicator used to select the A-to-D reference files is ATODGAIN.
Restrictions: The A-to-D lookup table is not accompanied by a data quality file. The header of the A-to-D lookup table image is a copy of the WFPC 2 science data header. The file must have four groups (one for each detector).
The following listing shows a partial image header for an A-to-D lookup table.
BITPIX = 16 / bits per data value I2
DATATYPE= INTEGER*2 / data type of the array C10
PTYPE10 = DATAMIN / minimum value of the data C08
PDTYPE10= REAL*4 C18
PSIZE10 = 32 I2
PTYPE11 = DATAMAX / maximum value of the data C08
PDTYPE11= REAL*4 C18
PSIZE11 = 32 I2
PTYPE21 = DETECTOR / CCD detector: PC 1, WFC 2-4 C08
PDTYPE21= INTEGER*4 C18
PSIZE21 = 32 I2
PTYPE23 = GOODMIN / minimum value of the "good" pixels C08
PDTYPE23= REAL*4 C18
PSIZE23 = 32 I2
PTYPE24 = GOODMAX / maximum value of the "good" pixels C08
PDTYPE24= REAL*4 C18
PSIZE24 = 32 I2
PTYPE25 = DATAMEAN / mean value of the "good" pixels C08 PDTYPE25= REAL*4 C18 PSIZE25 = 32 I2
PTYPE26 = GPIXELS / number of "good" pixels (DQF=0) C08
PDTYPE26= INTEGER*4 C18
PSIZE26 = 32 I2
PTYPE28 = CALIBDEF / number of "calibration defect" pixels (DQF=2) C08
PDTYPE28= INTEGER*4 C18 PSIZE28 = 32 I2 PTYPE29 = STATICD / number of "static defect" pixels (DQF=4) C08
PDTYPE29= INTEGER*4 C18
PSIZE29 = 32 I2
INSTRUME= WFPC2 / instrument in use C06 ROOTNAME= / rootname of the observation set C12
FILETYPE= A2D / file type: msk, a2d, bas, drk, flt, shd C03
MODE = / instr. mode: FULL (full res.), AREA (area int.) C04
SERIALS = / serial clocks: ON, OFF C03
IMAGETYP= SPECIAL / image type: EXT/BIAS/DARK.IFLAT/UFLAT/VFLAT/ECAL C18
CDBSFILE= ATOD / CDBS: YES/NO/BIAS/DARK/FLAT/MASK/ATOD/SHAD C18
DATE = / date file written (dd/mm/yy) C08
FILTNAM1= / first filter name C08
FILTNAM2= / second filter name C08
FILTER1 = / first filter number (0-48) I2
FILTER2 = / second filter number (0-48) I2
SHUTTER = / shutter in place during IFLAT: ( A or B) C01
ATODGAIN= / analog to digital gain (Electrons/DN) R4
EXPTIME = / exposure time (seconds) R4
TARGNAME= / target name C30
END
[Listing Version 01 24-MAY-1990]
7.2.4 Bias Files (BAS): <uniquename>.R2H
The structure in the electronic bias is removed by subtracting the bias reference file (with its accompanying data quality file).
Format: The bias reference file and its associated data quality file are REAL*4 image files with the same number of dimensions as the WFPC 2 science image. It is made from the average of a large number of bias readouts. The bias level removal correction must be done before averaging these files. This file therefore contains only the pattern superimposed upon the DC bias level.
Flags and Indicators: The flags and indicators used to select the bias reference files are MODE (which can take a value of either AREA or FULL) and ATODGAIN (which can take a value of either 7.0 or 15.0).
Restrictions: The bias reference file must be accompanied by a data quality file. The header of the bias image is a copy of the WFPC 2 science data header.
The following partial image header shows keywords used in the bias reference file.
BITPIX = 16 / bits per data value I2
DATATYPE= INTEGER*2 / data type of the array C10
PTYPE9 = DATAMIN / minimum value of the data C08
PDTYPE9 = REAL*4 C18
PSIZE9 = 32 I2
PTYPE10 = DATAMAX / maximum value of the data C08
PDTYPE10= REAL*4 C18
PSIZE10 = 32 I2
PTYPE19 = DETECTOR / CCD detector: PC 1, WFC 2-4 C08
PDTYPE19= INTEGER*4 C18
PSIZE19 = 32 I2
PTYPE23 = GOODMIN / minimum value of the "good" pixels C08
PDTYPE23= REAL*4 C18
PSIZE23 = 32 I2
PTYPE24 = GOODMAX / maximum value of the "good" pixels C08
PDTYPE24= REAL*4 C18
PSIZE24 = 32 I2
PTYPE25 = DATAMEAN / mean value of the "good" pixels C08
PDTYPE25= REAL*4 C18
PSIZE25 = 32 I2
PTYPE26 = GPIXELS / number of "good" pixels (DQF=0) C08
PDTYPE26= INTEGER*4 C18
PSIZE26 = 32 I2
PTYPE28 = CALIBDEF / number of "calibration defect" pixels (DQF=2) C08
PDTYPE28= INTEGER*4 C18
PSIZE28 = 32 I2
PTYPE29 = STATICD / number of "static defect" pixels (DQF=4) C08
PDTYPE29= INTEGER*4 C18
PSIZE29 = 32 I2
INSTRUME= WFPC2 / instrument in use C06
ROOTNAME= / rootname of the observation set C12
FILETYPE= BAS / file type: msk, a2d, bas, drk, flt, shd C03
MODE = / instr. mode: FULL (full res.), AREA (area int.) C04
SERIALS = / serial clocks: ON, OFF C03
IMAGETYP= SPECIAL / image type: EXT/BIAS/DARK/IFLAT/UFLAT/VFLAT/ECAL C18
CDBSFILE= BIAS / CDBS: YES/NO/BIAS/DARK/FLAT/MASK C18
DATE = / date file written (dd/mm/yy) C08
FILTNAM1= / first filter name C08
FILTNAM2= / second filter name C08
FILTER1 = / first filter number (0-48) I2
FILTER2 = / second filter number (0-48) I2
SHUTTER = / shutter in place during IFLAT (A or B) C01
ATODGAIN= / analog to digital gain (Electrons/DN) R4
EXPTIME = / exposure duration (seconds) -- calculated R4
TARGNAME= / target name C30
END
[Listing Version 01 09-JUL-1992]
7.2.5 Dark Files (DRK): <uniquename>.R3H
The WFPC 2 dark reference file and its associated data quality file are used to correct the dark current. The WFPC 2 CCDs generate a spurious signal during exposures know n as dark current. This signal is a function of the time since the last erase command and the operating temperature of the CCD detectors and varies from pixel to pixel. The dark reference file is scaled by the time since the last erase command and subtracted from the image.
Format: The dark reference file is a single-precision (REAL*4) image file with the same number of dimensions as the WFPC 2 science image. It is made from the average of a large number of dark images. The bias level removal and bias image subtraction corrections must be done to these files prior to averaging. Ideally, the CCD detectors should not have been saturated by sources for several hours prior to the acquisition of the dark images used to make this reference file. The dark reference file must be scaled to the equivalent of a 1-second exposure.
Flags and Indicators: The flags and indicators used to select the dark reference files are MODE (which can be either AREA or FULL), SERIALS (which can be either ON or OFF), and ATODGAIN (which can be either 7.0 or 15.0).
Restrictions: The dark reference file must be accompanied by a data quality file. The header of the dark reference file is a copy of the WFPC 2 science data header.
The following listing shows a partial image header for a sample dark reference file.
BITPIX = 16 / bits per data value I2
DATATYPE= INTEGER*2 / data type of the array C10
PTYPE9 = DATAMIN / minimum value of the data C08
PDTYPE9 = REAL*4 C18
PSIZE9 = 32 I2
PTYPE10 = DATAMAX / maximum value of the data C08
PDTYPE10= REAL*4 C18
PSIZE10 = 32 I2
PTYPE19 = DETECTOR / CCD detector: PC 1, WFC 2-4 C08
PDTYPE19= INTEGER*4 C18
PSIZE19 = 32 I2
PTYPE23 = GOODMIN / minimum value of the "good" pixels C08
PDTYPE23= REAL*4 C18
PSIZE23 = 32 I2
PTYPE24 = GOODMAX / maximum value of the "good" pixels C08
PDTYPE24= REAL*4 C18
PSIZE24 = 32 I2
PTYPE25 = DATAMEAN / mean value of the "good" pixels C08
PDTYPE25= REAL*4 C18
PSIZE25 = 32 I2
PTYPE26 = GPIXELS / number of "good" pixels (DQF=0) C08
PDTYPE26= INTEGER*4 C18
PSIZE26 = 32 I2
PTYPE28 = CALIBDEF / number of "calibration defect" pixels (DQF=2) C08
PDTYPE28= INTEGER*4 C18
PSIZE28 = 32 I2
PTYPE29 = STATICD / number of "static defect" pixels (DQF=4) C08
PDTYPE29= INTEGER*4 C18
PSIZE29 = 32 I2
INSTRUME= WFPC2 / instrument in use C06
ROOTNAME= / rootname of the observation set C12
FILETYPE= DRK / file type: msk, a2d, bas, drk, flt, shd C03
MODE = / instr. mode: FULL (full res.), AREA (area int.) C04
SERIALS = / serial clocks: ON, OFF C03
IMAGETYP= SPECIAL / image type: EXT/BIAS/DARK/IFLAT/UFLAT/VFLAT/ECAL C18
CDBSFILE= DARK / CDBS: YES/NO/BIAS/DARK/FLAT/MASK/ATOD/SHAD C18
DATE = / date file written (dd/mm/yy) C08
FILTNAM1= / first filter name C08
FILTNAM2= / second filter name C08
FILTER1 = / first filter number (0-48) I2
FILTER2 = / second filter number (0-48) I2
SHUTTER = / shutter in place during IFLAT (A or B) C01
ATODGAIN= / analog to digital gain (Electrons/DN) R4
EXPTIME = / exposure duration (seconds) -- calculated R4
TARGNAME= / target name C30
END
Listing Version 01 09-JUL-1992]
7.2.6 Flat Field Reference Files (FLT): < uniquename>.R4H
The variations in sensitivity between pixels in the CCD detectors are corrected by applying a flat field reference file. This file contains the normalized inverse sensitivity (gain) for each pixel in the detector. It is made from internal flat lamp exposures, the combination of streaked earth flats or processed observations of astronomical sources. The image is multiplied by the flat field file after correcting for bias and dark.
The flat field reference file is a single-precision (REAL*4) image file with the same number of dimensions as the WFPC 2 science image. The bias level removal and bias image subtraction corrections must be done to these files. The dark correction is not usually relevant to the short, bright flat field exposures (but may be in some cases). The flat fields must be normalized to 1.0 and inverted (1/x) to allow the correction process to use multiplication. Normalization should be based on all pixels not flagged in the flat field file’s data quality file in all four detectors (groups). It is important that the range of values in the flat field files have reasonable limits. Pixels that fall outside the acceptable range of sensitivity, or which are located in dead regions, should be set to 1 in the flat field file and flagged in the data quality file.
Flags and Indicators: The flags and indicators used to select the flat field reference files are MODE (the mode can be either AREA or FULL), FILTNAM1, and FILTNAM2. There are 71 filter elements; in addition, some filter elements can be used in combination with others. The variety of modes plus the time-dependencies of some of the flat fields requires that several hundred WFPC 2 flat fields reside in CDBS.
Restrictions: The flat field reference file must be accompanied by a data quality file. The header of the flat field reference file is a copy of the WFPC 2 science data header.
The following listing shows a partial image header from a sample flat field reference file.
BITPIX = 16 / bits per data value I2
DATATYPE= INTEGER*2 / data type of the array C10
PTYPE9 = DATAMIN / minimum value of the data C08
PDTYPE9 = REAL*4 C18
PSIZE9 = 32 I2
PTYPE10 = DATAMAX / maximum value of the data C08
PDTYPE10= REAL*4 C18
PSIZE10 = 32 I2
PTYPE19 = DETECTOR / CCD detector: PC 1, WFC 2-4 C08
PDTYPE19= INTEGER*4 C18
PSIZE19 = 32 I2
PTYPE23 = GOODMIN / minimum value of the "good" pixels C08
PDTYPE23= REAL*4 C18
PSIZE23 = 32 I2
PTYPE24 = GOODMAX / maximum value of the "good" pixels C08
PDTYPE24= REAL*4 C18
PSIZE24 = 32 I2
PTYPE25 = DATAMEAN / mean value of the "good" pixels C08
PDTYPE25= REAL*4 C18
PSIZE25 = 32 I2
PTYPE26 = GPIXELS / number of "good" pixels (DQF=0) C08
PDTYPE26= INTEGER*4 C18
PSIZE26 = 32 I2
PTYPE28 = CALIBDEF / number of "calibration defect" pixels (DQF=2) C08
PDTYPE28= INTEGER*4 C18
PSIZE28 = 32 I2
PTYPE29 = STATICD / number of "static defect" pixels (DQF=4) C08
PDTYPE29= INTEGER*4 C18
PSIZE29 = 32 I2
INSTRUME= WFPC2 / instrument in use C06
ROOTNAME= / rootname of the observation set C12
FILETYPE= FLT / file type: msk, a2d, bas, drk, flt, shd C03
MODE = / instr. mode: FULL (full res.), AREA (area int.) C04
SERIALS = / serial clocks: ON, OFF C03
IMAGETYP= SPECIAL / image type: EXT/BIAS/DARK/IFLAT/UFLAT/VFLAT/ECAL C18
CDBSFILE= FLAT / CDBS: YES/NO/BIAS/DARK/FLAT/MASK/ATOD/SHAD C18
DATE = / date file written (dd/mm/yy) C08
FILTNAM1= / first filter name C08
FILTNAM2= / second filter name C08
FILTER1 = / first filter number (0-48) I2
FILTER2 = / second filter number (0-48) I2
SHUTTER = / shutter in place during IFLAT (A or B) C01
ATODGAIN= / analog to digital gain (Electrons/DN) R4
EXPTIME = / exposure duration (seconds) -- calculated R4
TARGNAME= / target name C30
END
[Listing Version 01 09-JUL-1992]
7.2.7 Shutter Shading Reference Files (SHD): <uniquename>.R5H
When a WFPC 2 exposure is relatively short, shutte r shading (resulting from the finite time of flight of the shutter blade) gives rise to uneven illumination across the field of view. It is corrected by applying the shutter shading reference file in the following way:
output = input * (1 + reference time x shutter shading/exposure time)
where reference time is 1 second.
Format: The shutter shading reference file is a single-precision (REAL*4) image file with the same number of dimensions as the WFPC 2 science image.
Flags and Indicators: The flags and indicators used to select the shutter shading reference files are SHUTTER (which can have the value A or B) and MODE (which can be AREA or FULL).
Restrictions: The shutter shading reference file is not accompanied by a data quality file. The header of the shutter shading reference file is a copy of the WFPC 2 science data header.
The following listing shows a partial image header from a sample flat field reference file.
BITPIX = 16 / bits per data value I2
DATATYPE= INTEGER*2 / data type of the array C10
PTYPE9 = DATAMIN / minimum value of the data C08
PDTYPE9 = REAL*4 C18
PSIZE9 = 32 I2
PTYPE10 = DATAMAX / maximum value of the data C08
PDTYPE10= REAL*4 C18
PSIZE10 = 32 I2
PTYPE19 = DETECTOR / CCD detector: PC 1, WFC 2-4 C08
PDTYPE19= INTEGER*4 C18
PSIZE19 = 32 I2
PTYPE23 = GOODMIN / minimum value of the "good" pixels C08
PDTYPE23= REAL*4 C18
PSIZE23 = 32 I2
PTYPE24 = GOODMAX / maximum value of the "good" pixels C08
PDTYPE24= REAL*4 C18
PSIZE24 = 32 I2
PTYPE25 = DATAMEAN / mean value of the "good" pixels C08
PDTYPE25= REAL*4 C18
PSIZE25 = 32 I2
PTYPE26 = GPIXELS / number of "good" pixels (DQF=0) C08
PDTYPE26= INTEGER*4 C18
PSIZE26 = 32 I2
PTYPE28 = CALIBDEF / number of "calibration defect" pixels (DQF=2) C08
PDTYPE28= INTEGER*4 C18
PSIZE28 = 32 I2
PTYPE29 = STATICD / number of "static defect" pixels (DQF=4) C08
PDTYPE29= INTEGER*4 C18
PSIZE29 = 32 I2
INSTRUME= WFPC2 / instrument in use C06
ROOTNAME= / rootname of the observation set C12
FILETYPE= SHD / file type: msk, a2d, bas, drk, flt, shd C03
MODE = / instr. mode: FULL (full res.), AREA (area int.) C04
SERIALS = / serial clocks: ON, OFF C03
IMAGETYP= SPECIAL / image type: EXT/BIAS/DARK/IFLAT/UFLAT/VFLAT/ECAL C18
CDBSFILE= SHAD / CDBS: YES/NO/BIAS/DARK/FLAT/MASK/ATOD/SHAD C18
DATE = / date file written (dd/mm/yy) C08
FILTNAM1= / first filter name C08
ILTNAM2= / second filter name C08
FILTER1 = / first filter number (0-48) I2
FILTER2 = / second filter number (0-48) I2
SHUTTER = / shutter in place during IFLAT (A or B) C01
ATODGAIN= / analog to digital gain (Electrons/DN) R4
EXPTIME = / exposure duration (seconds) -- calculated R4
TARGNAME= / target name C30
END
[Listing Version 01 09-JUL-1992]