Validation of 2MASS V3 Image Product

Summary

This page summarizies validation done on the 2MASS V3 Image Product. The images are produced and used for galaxy processing during the 2MASS 2MAPPS pipeline processing. At the completion of the scan processing for each night the night is calibrated, and then all the image headers for that night are updated with the zero points adjusted for the calibrated zero point corrections and the extinction corrections. These images are written to tape, and also compressed using the STSCI Hcompress program and copied to the on-line compressed image archive for use by the quicklook image visualizer.

The validation of the image products includes the following:

  • Assuring all compressed images are on line for that set of survey scans processed for V3.
  • Checking a primary subset of items in all the fits headers for accuracy, including the astrometric and photometric information. This will assure that each grid on line has the proper astrometric keywords and the calibrated zero point was updated and accurate.
  • Spot checking a subset of images for photometric and astrometric accuracy using DAOPHOT, the community standard photometric package. These checks found no problems with either the photometry or astrometry of the images.

    Additional validation of the image product comes from the demonstrated astrometry and photometry of the 2MASS extended source processing , which was done using the 2MASS image product, and the extensive use of the 2MASS v3 visualizer which uses the compressed image archive.

    Validation

    Pursuant to accounting for the images and checking the fits headers in the on-line archive, a program was written to read the calibration files (cYYMMDD.cal and pipe.cal) from the 2MAPPS V3 on-line processing archive, and for each survey scan processed in V3, read the corresponding fits headers from the on-line image archive, output a critical subset of the astrometric and photometric header information, range check them, and recompute the calibrated zero point (MAGZP) and assure the information from the header agrees to 0.01 magnitude. This process checked for:

  • MAGZP > 18.0 && |MAGZP- recalulation| < 0.01 magnitude
  • 0.87 < SEESH < 1.4
  • 3600*CDELT2 = 1 arcsec 

                        north        south       total
scans processed       30269        40443       70712
scans downgraded 0       15           37          52
images archived     2088561      2790567     4879128
seeing range  error       0           15          15
read errors               0            0           0
null header values        0            0           0
zero point errors         0            0           0

    There are 15 images with SEESH = 4.00 in the headers all from scans 000211s/s013,014, & 021. The seestatus, coadd log, and values passed to PROPHOT were all properly in the range 0.95-1.05. This phenomenon was traced to a bug in the header update program which caused it to pick up the wrong value when two columns were not separated by whitespace. This bug was only triggered in 15 cases out of 4879128. A fix has been tested and is being implemented to correct this problem in the on-line and tape archives.

    The right ascension, declination, seeing shape parameter, and other parameters in the image headers are also extracted from the coadd processing logs and may be found in the coadd_dat database table. Range checking on the coadd_dat table in the V3 database may be found here.

    The following plots show the full range of the parameters for the photometric survey scans selected for the V3 catalog. In the first 2 plots, all three bands are plotted, separating into 3 groups with J on top, then H and Ks.

    Northern Telescope Image Keyword Zeropoint vs Airmass

    Southern Telescope Image Keyword Zeropoint vs Airmass

    Image Keyword Declination vs Right Ascension

    This page last updated on Sept 3, 2002.

    Gene Kopan - gene at ipac.caltech.edu