2MASS QUALITY ASSURANCE
AND DATA VALIDATION

I. Objectives and Scope

• Assure that Survey data meets Level 1 Science Requirements.
  
  
• Provide rapid turn-around Telescope/Camera System health monitor.
  
  
• Monitor long-term instrumental trends for the Survey.
  
  
• Essential for System that must process ~15GB / night / telescope
  
  
• QUALITY Subsystem will provide information for designated 2MASS Team member, in conjunction with IPAC analysts, to sign off on every survey scan.
  
  
• Assign quality indicator to every scan and feed back to survey scheduler.
  
  

II. Implementation

III. Levels of Quality Control

• Nightly:
  
  
  1. Verify tape and raw data integrity:
  
  
  - Are tapes readable?
  - Do tape contents agree with observatory tape log?
  
  
  2. Monitor health of Camera/Telescope:
  
  
  - Pointing, tracking and scanning.
  - Focus/Image quality.
  - System gain and sensitivity.
  - Array health (bias and responsivity).
  
  
  3. Evaluate photometric quality of night (calibration scan analysis):
  
  
  - Gross photometric characteristics (zero point stability and extinction terms).
  - Photometric repeatability and sensitivity.
  - Seeing and background range and variation.
  
  
  4. Verify quality of data within each scan:
  
  
  - Diagnostics from each 2MAPPS subsystem to assess quality of data and processing.
  - Flat, bad pixel maps, sky stats reasonable? (DARKS, DFLAT, PIXPHOT)
  - Pointing terms, scan/dither pattern and residuals reasonable? (POSMAN)
  - Source density reasonable for latitude? (PIXPHOT, GALWORKS)
  - Is scan within seeing limits? (SEEMAN)
  - Are photometric corrections reasonable? (MAPCOR)
  - Are extended source parameters and thresholds reasonable? (GALWORKS)
  
  
  5. Verify scan-to-scan consistency within a night:
  
  
  - Photometric and positional consistency in scan overlap regions.
  - Completeness estimates from overlap (# repeats vs. magnitude).
  - Fractions of sources with various band combinations.
  - Position comparisons with Tycho and USNOA optical catalogs.
  
  
• Longer Term Database Functions:
  
  
  1. As each new scan is loaded in Survey Database, verify scan quality through comparison with other nights:
  
  
  - Analyze multiple sightings for photometric and positional consistency in Point and Extended Source Working Database.
  - Search for missing sources (i.e. sources previously detected not found, and new sources not previously detected).
  
  
  2. Weekly or Monthly examine large scale photometric and astrometric uniformity.
  
  3. Monitor long-term trends in photometric zero points and extinction terms and update and improve standard star archive photometry.
  
  
• End of Survey:
  
  
  1. Complete reprocessing of data with optimal parameters, and full scan overlap information.
  
  

IV. Basic Acceptance Criteria For Survey Scan

1. Tape successfully validates.
   
2. Instrumental Calibration images (DARKS, FLATS) within nominal ranges.
   
3. Photometric quality of night passes minimum acceptable criteria.
   
4. Nominal sensitivity of camera as gauged from calibration scan repeats is within Level 1 specifications, in context of seeing and BG conditions.
   
5. System gain (DN->mJy) is within nominal limits.
   
6. Nightly averaged scan step size and array rotations within tolerances for optimal dithering pattern.
   
7. Optical system does not exhibit problems related to focus, distortion, etc.
   
   

1. Scan is bounded in time by at least 3 valid calibration intervals.
   
2. Scan data nominally completes processing. If processing fails, determine
   if due to data or processing related reasons. If data-related, mark scan as having failed Q/A and request rescan. If processing related, queue for reprocessing.
   
3. Camera/Telescope operating within nominal limits, as determined from:
   
   
   a. Scan Step Size
   b. Array Rotation Angles
   c. Telescope Pointing
   e. Band-band array alignment
   f. R1 vs. R2-R1 registration
   
   
4. Output data passes basic value checking:
   
   
   a. RA and DEC min/max within corners?
   b. Magnitudes within physical range?
   
   
5. Frame background (BG) levels do not exceed maximum allowable value in any band.
   
6. BG variations indicate no clouds (no frame-frame BG variations exceeding 1-sigma (BG)) (3.7um sky channel?)
   
7. Seeing does not exceed maximum allowable value at any time during scan (3.5 arc-seconds FWHM - TBD).
   
8. Seeing does not vary faster than it can be reliably tracked for star galaxy separation.
   
9. Relative numbers of sources detected in each band is consistent with galactic location.
   
10. Reconstructed positions of astrometric reference stars within Level 1 Specifications (1-sigma < 0.5" for SNR>20).
    
11. Net position uncertainties from bandmerging within acceptable limits.
    
12. Net position uncertainties with respect to high density optical catalogs within acceptable limits (TBD).
    
13. External reliability as gauged by optical source associations within minimum limits (taking environment into account)
    
14. If scan is in contiguous block, photometric and astrometric dispersion with adjacent scans satisfies Level 1 Specifications.
    
15. Other subsystem quality indicators:....