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2MASS Final Release Validation Page

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The page summarizes the validation tasks being performed on the final release catalog datasets for 2MASS. The aims of this process are to

• ensure that the distributed results are globally consistent with the project's Level 1 specifications and expectations of overall quality and uniformity.
• inspect the dataset for local significant violations of specifications which may not appear in global analyses
• track the efficacy of corrections applied to the data
• provide characterization of the release datasets to aid users analyses via explanatory material.

1. Sky Coverage

   - Effective coverage for Images, PSC, XSC -- where are the holes?
        -- Does sum of sources per scan used equal total draw?
        -- Does the distribution of release sources reflect the
             tile boundaries
        -- Do "A" sources have the same spatial distribution as the
            tile boundaries
   - Effect of Bright Stars and Large Galaxies
        -- Compile total area "lost" to bright stars (will depend
          on flagging -- star blanking areas are not "opaque")
        -- Stack many different bright stars and plot nearby points
   
2. Sensitivity, Completeness and Reliability  (Level 1 Specifications)

   -- Atmospheric Effects (PSP+zero point maps)
   -- Source Density/Confusion Effects (Point and Extended Source count slope
        and roll-over maps, mean color distributions)
   -- System Effects (telescope, camera, software)
           effects of J-band zeropoint variation, array change,
           primary mirror washing, recollimation, image elongation.
   -- Calibration scan repeatability analysis -- Completeness/reliability

3. Astrometry

   - Independent confirmation by Zacharias
   - Mean accuracy with respect to Tycho 2 and other large scale
        external catalogs, such as UCAC, FIRST (for extended sources)
   - Internal consistency (scan overlaps)
   - Large-scale trends (cross-scan position, pole dependencies)
   - Characterization of astrometric uncertainties

4. Photometry (PSC and XSC)

   - Internal Consistency (repeatability, overlaps)
   - Uniformity (mean colors, CMDs, color maps, star-counts rollover,
          -- evaluate for regions of different spatial dimension
             (great circles, declination bands...)
          -- Fundament question:  How to tune selection to remove 
              survey scan pattern systematics
    - Large-scale trends 
        cross-scan, confusion, seeing shape dependence,
	background/zeropoint dependence
        -- Look at histogram of prox vs. seeing
   - Nature and origin of sources with obviously wrong colors 
         -- exploit new image servers
         -- tchester looks at xsc
   - Statistics of SNR's and _msigs
         -- global validation of cmsig (range check)
         -- range check msigcom
   - Characterization of aperture photometry vs. PSF photometery
         -- develop rules for user to favor aperture over psf 
   - Photometric characteristics vs. proximity
   - Characterization of the photometric quality flag.
         -- outline rationale for flagging and suggested uses
   - Comparison with 2nd Incremental release 
         -- join catalogs look for expected and unexpected deltas
 

5. Photometric System and Calibration

   - Calibration uniformity/stability (photometry of standards in PSC)
   - System transformations
   - Absolute Calibration
   - North vs. South overlap
       -- mean colors between hemispheres
       -- duplicate whole tiles
6. Comparison to External Catalogs

      Huchra XSC
      NOAO wide deep
      Sloan

7. General and Sanity Checks

   - Range Checking
   - All sky flux, counts, and color maps
   - Comparison to Galactic star counts models
   - Angular correlation functions and edge detection
   - Hemispheric boundary effects
   - Linearity (comparison with deep coadds)