II. User's Guide to the WISE Preliminary Data Release

4. Ancillary Products

h. Single-Exposure (L1) Image Inventory Table Format

The following table contains brief descriptions of all metadata information characterizing single-exposure image frames. The table also contains some processing-specific information, such as the date and time when the archive preparation software was run, and basic photometric parameters used for photometry.

The columns in the following table are:

Column NameFormatUnitsnullsDescription 
band %1d ---- no WISE band number for the image.  
naxis %1d ---- no Number of data axes; it is always '2' for two-dimensional images.  
naxis1 %4d pixels no Length of data axis 1 or number of columns in the image.  
naxis2 %4d pixels no Length of data axis 2 or number of rows in the image.  
wrelease %20s ---- no The version number of the WISE multiframe pipeline used for this current data release.  
crpix1 %6.1f pixel no Axis 1 reference pixel at position crval1,crval2: 0.5*(naxis1+1)  
crpix2 %6.1f pixel no Axis 2 reference pixel at position crval1,crval2: 0.5*(naxis2+1)  
crval1 %16.12f degrees no Reference Right Ascension at crpix1,crpix2 for EQUINOX.  
crval2 %16.12f degrees no Reference Declination at crpix1,crpix2 for EQUINOX.  
ctype1 %13s ---- no Projection type for axis 1. It is always set to use the SIN (orthographic) projection; for the definition, see Calabretta & Greisen, 2002.  
ctype2 %13s ---- no Projection type for axis 2. It is always set to use the SIN (orthographic) projection; for the definition, see Calabretta & Greisen, 2002.  
equinox %6.1f degrees no Equinox of the World Coordinate System (WCS).  
bunit %20s ---- no Image pixel units: Data Number (DN) for intensity and uncertainty filetypes; the mask filetype is unitless. Image filetypes are described in section IV.3a.  
elon %16.12f degrees no Ecliptic longitude of the reference pixel. CAUTION: This coordinate should not be used as an astrometric reference.  
elat %16.12f degrees no Ecliptic latitude of the reference pixel. CAUTION: This coordinate should not be used as an astrometric reference.  
glon %16.12f degrees no Galactic longitude of the reference pixel. CAUTION: This coordinate should not be used as an astrometric reference.  
glat %16.12f degrees no Galactic latitude of the reference pixel. CAUTION: This coordinate should not be used as an astrometric reference.  
ra1 %16.12f degrees no Right ascension (J2000) at corner #1 (crpix1,crpix2=-0.5,-0.5)  
dec1 %16.12f degrees no Declination (J2000) at corner #1 (crpix1,crpix2=-0.5,-0.5)  
ra2 %16.12f degrees no Right ascension (J2000) at corner #2 (crpix1,crpix2=naxis1+0.5,-0.5)  
dec2 %16.12f degrees no Declination (J2000) at corner #2 (crpix1,crpix2=naxis1+0.5,-0.5)  
ra3 %16.12f degrees no Right ascension (J2000) at corner #3 (crpix1,crpix2=naxis1+0.5,naxis2+0.5)  
dec3 %16.12f degrees no Declination (J2000) at corner #3 (crpix1,crpix2=naxis1+0.5,naxis2+0.5)  
ra4 %16.12f degrees no Right ascension (J2000) at corner #4 (crpix1,crpix2=-0.5,naxis2+0.5)  
dec4 %16.12f degrees no Declination (J2000) at corner #4 (crpix1,crpix2=-0.5,naxis2+0.5)  
magzp %9.5f mag no Relative photometric zero-point magnitude for the image.  
magzpunc %9.6f mag no 1-sigma uncertainty in the photometric zero-point magnitude for the image.  
scan_id %6s ---- no Scan identifier. This is a six character string that identifies a block of survey exposures that are acquired between two flight system maneuvers, such as reorientation of the instrument boresight near the ecliptic poles, or slews to acquire TDRSS for data downlink contacts. Because maneuvers often take place near the ecliptic poles, the scan number is roughly associated with a half-orbit's worth of images. However, scans can cover less or more than half of the arc between ecliptic poles.

The scan_id has the general form SSSSSx, where

  • SSSSS is a zero-filled, five-digit integer that is twice the WISE orbit number. The orbit number increments each time the flight system passes the north ecliptic pole (NEP). Orbit number 1 was defined to start with the fictitious NEP passage immediately prior to WISE launch.

  • x   is a letter assigned based on sequential count of scans started in a specific half-orbit. The first scan has x="a", the next x="b", up to a maximum of x="d" for scans in the Preliminary Release.

The first scan whose data are used in the Preliminary Data Release is scan 00936a. This was the first scan after the NEP crossing in the 468th WISE orbit. The final scan included in the Release is 04125a, the first scan after the SEP crossing in the 2062nd WISE orbit.

 
scangrp %2s ---- no Scan group identifier (the last two characters of the scan_id, used to group scan data on the disks).  
frame_num %3d ---- no Number of the frameset for this image. The identifier has the general form MMM, a zero-filled three-digit number.

The frameset number is computed based on time bins which count from the scan start time:

fr_num = int[(((frame_utc - dt_beg) - scan_start_utc)/bin_size] + 1

where

  • int[] means truncate to an integer
  • frame_utc is the nominal frame exposure center UTC (when the boresite crosses the image center) in seconds
  • dt_beg is 4.4s. This is a nominal offset to approximate when the exposure began
  • scan_start_utc is the scan start time in seconds
  • bin_size is 10s.

For example, a frame with a start time 1234 secs after the scan start time would have a frame number of 124.

N.B.

  • Frame_num is not a frameset sequence number

  • As a result of using a 10 sec bin, every 11th frame skips a number, so it is normal to see breaks in the frame numbering and it doesn't indicate missing data.

  • Because frameset numbering is based on the predicted scan start time from the survey plan, and because frameset data may not start being acquired until well after the start of the scan, frameset numbers often do not start at 1 for a scan.
 
l0file %200s ---- no The corresponding level 0 image file name.  
date_obs %24s datetimeZ no The date and time of the mid-point of the frameset exposure, in UTC. The mid-point is defined as the time the optical boresight crosses the center of the WISE focal planes. This time is the same for all bands, whereas the exposure times in W1 and W2 are different than in W3 and W4.  
mjd_obs %14.8f mjdate no The Modified Julian Date of the mid-point of the frameset exposure.  
dtanneal %18.11f seconds no Elapsed time in seconds since the last anneal.  
utanneal %24s datetimeZ no The date and time of the last anneal, UTC.  
unixt %16.5f seconds no UNIX date-time in seconds of the mid-point of the frameset exposure, in UTC. The mid-point is defined as the time the optical boresight crosses the center of the WISE focal planes. This time is the same for all bands, whereas the exposure times in W1 and W2 are different than in W3 and W4.  
ephemt %16.6f seconds no Ephemeris date-time in seconds of the mid-point of the frameset exposure, in UTC. The mid-point is defined as the time the optical boresight crosses the center of the WISE focal planes. This time is the same for all bands, whereas the exposure times in W1 and W2 are different than in W3 and W4.  
exptime %4.1f seconds no Single image frame exposure time in seconds; exposure times in W1 and W2 are different than in W3 and W4.  
tsamp %4.1f seconds no The time interval between non-destructively read samples-up-the-ramp in on-board processing.  
wcdelt1 %21.18f degrees/pixel no Axis 1 pixel scale at the reference pixel crpix1, crpix2, in degrees per pixel. See pxscal1 for the arcsec equivalent.  
wcdelt2 %21.18f degrees/pixel no Axis 2 pixel scale at the reference pixel crpix1, crpix2, in degrees per pixel. See pxscal2 for the arcsec equivalent.  
crder1 %20.14e degrees no Uncertainty in crval1 (right ascension).  
crder2 %20.14e degrees no Uncertainty in crval2 (declination).  
csdradec %20.14f degrees no Costandard deviation in crval1 and crval2 (RA and Dec), the square root of the absolute value of the covariance between RA and Dec with the sign of the covariance re-attached to the square-root if it was originally negative.  
pxscal2 %17.14f arcsec/pixel no Axis 1 arcsec per pixel scale at the reference pixel crpix1, crpix2.  
pxscal2 %17.14f arcsec/pixel no Axis 2 arcsec per pixel scale at the reference pixel crpix1, crpix2.  
uncrts1 %20.14e degrees/pixel no Uncertainty in the pixel scale wcdelt1.  
uncrts2 %20.14e degrees/pixel no Uncertainty in the pixel scale wcdelt2.  
wcrota2 %18.13f degrees no Image twist: the position of the image y-axis (axis2) West of North at the EQUINOX in the opposite direction of the conventional Position Angle, where position angle (P.A.) = -CROTA for J2000.  
pa %18.13f degrees no The position angle of the positive image y-axis (axis2), East of North at the EQUINOX.  
uncrtpa %21.18f degrees no The uncertainty in the position angle (PA).  
skew %5.1f ---- no The measurement of non-orthogonality of the image frame axes.  
cd1_1 %21.18f degrees/pixel no WCS rotation matrix element 1,1 encoding frame rotation and pixel scale.  
cd1_2 %21.18f degrees/pixel no WCS rotation matrix element 1,2 encoding frame rotation and pixel scale.  
cd2_1 %21.18f degrees/pixel no WCS rotation matrix element 2,1 encoding frame rotation and pixel scale.  
cd2_2 %21.18f degrees/pixel no WCS rotation matrix element 2,2 encoding frame rotation and pixel scale.  
debgain %10.3f e-/DEB ADU no On-board Digital Electronics Box gain (with units of e-/observed DN). This factor is used to convert DN to electrons.  
febgain %10.4f e-/SUR ADU no Flight electronics box gain for individual non-destructive read samples up-the-ramp.  
qa_status %9s ---- no This string indicates Quality Assurance status for the scan and frameset:
  • "Prelim" means only preliminary Quality Assurance has been performed by the automated QA subsystem;
  • "Reviewed" means the QA data has been examined and scores corrected by a QA team member;
  • "Final" means the QA scores have been finalized.
 
qual_frame %2d ---- no This integer indicates the quality score value for the Single-exposure image frameset, with values of 0 (poor quality), 5, or 10 (high quality). The value is determined by the minimum of the quality factors qc_fact, qn_fact, and qi_fact, multiplied by ten.  
qc_fact %3.1f ---- no This quality factor gauges the quality of completion of the Single-exposure image frameset. If the status value from the processing pipeline was equal to 0 (indicating a problem-free completion), then qc=1.0. Otherwise, qc=0.0 because the frameset failed to complete processing. All framesets in the Database have received qc values of 1.0.  
qi_fact %3.1f ---- no This quality factor gauges the image shape quality of the Single-exposure image frameset. It checks for potential image smearing by using the axial ratio of the PSF calculated from a subset of sources in the frameset. The value of qi is 1.0 if the axial ratio b/a > 0.60; otherwise it is 0.0.  
qn_fact %3.1f ---- no This quality factor indicates the background and noise characteristics quality of the Single-exposure frameset.  
qa_fact %3.1f ---- no This quality factor gauges the astrometric quality. If the standard deviation of WISE positions with respect to the 2MASS Point Source Catalog positions is < 0.5 arcsec on each axis (or 0.71 arcsec RSS), for sources having SNR > 20 in at least one band, then qa=1.0. Otherwise, qa=0.0  
qual_scan %2d ---- no This integer indicates the quality score value for the scan containing the Single-exposure image frameset, with values of 0 (poor quality), 5, or 10 (high quality). The value is determined by the minimum of the quality factors qs1_fact, qs5_fact, and qp_fact, multiplied by ten.  
qs1_fact %3.1f ---- no This quality factor indicates the quality of scan synchronization as judged from the overall 1x1 PSF grid computed by the PSF Moments routine and evaluated based on the effective number of noise pixels.  
qs5_fact %3.1f ---- no This quality factor indicates the quality of scan synchronization as judged from the overall 5x5 PSF grid computed by the PSF Moments routine and evaluated based on the effective number of noise pixels.  
qp_fact %3.1f ---- no This quality factor indicates the scan photometric quality. If the scan's photometric zero-point offset computed using profile-fit photometry (pzp) falls within a certain range about 0, the value of qp_fact is 1.0; otherwise it is 0.0.  
qs_fact %4.1f ---- no This quality factor is not currently used.  
date_imgprep %20s datetimeZ no The date and time when the data was prepared by the WISE archive software DBPREP for the archive loading, in UTC.  
load_id %4d ---- no A unique integer that identifies the archive data load batch in the archive ingest procedure that contains the frame image.  
cntr %12d ---- no Unique sequential identification number for the image metadata table entry.  

Last Update: 2011 April 13

Previous page    Next page
Return to Explanatory Supplement TOC