2MASS QUALITY SUBSYSTEM
PARAMETER REVIEW

I. QUALITY Objectives

• ENFORCER of the Level 1 Science Requirements.
  
  
• Rapid turn-around Telescope/Camera System health monitoring.
  
  
• Monitor long-term instrumental and site trends for the Survey.
  
  
• 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. Basic Acceptance Criteria For Survey Scan

1. Tape is readable and contents agree with log file.
   
2. Difference between nightly Instrumental Calibration images and canonicals within threshold.
   
3. Photometric quality of night passes minimum acceptable criteria.
   
4. Nominal sensitivity of detectors 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. Rescan if data-related failure, reprocess if processing related.
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 levels do not exceed maximum allowable value in any band.
   
6. Background variations indicate no clouds (no frame-frame BG variations exceeding 1-sigma) (3.7um sky channel?)
7. Image shape (focus) within tolerances.
8. Seeing FWHM does not exceed maximum allowable value at any time during scan (3.5 arc-seconds FWHM - TBD).
   
9. Seeing variations smaller than threshold for tracking reliability in star-galaxy separation.
   
10. Relative source detections in each band consistent with galactic location.
    
11. Net band-band position uncertainties from bandmerging within acceptable limits.
    
12. Reconstructed positions of Tycho stars within Level 1 Specifications.
    
13. Number and distribution of Tycho stars sufficient for accurate solution.
    
14. Net position uncertainties with respect to high density optical catalogs within acceptable limits.
    
15. External reliability as gauged by optical source associations within minimum limits (taking environment into account)
    
16. Photometric and astrometric dispersion with adjacent scans satisfies Level 1 Specifications. If scan is in contiguous block,
    
17. Other subsystem quality indicators:....
    
    

IV. Sample QA Parameters By Subsystem

1. Tape Format and Contents

1. Intrinsic dispersion in darks and flats
   
2. Numbers of masked pixels
   
3. Variation of nightly darks and flats with respect to canonicals
   

1. Average dispersion in sky-offset frames in each scan
   

1. Average, minimum and maximum frame background values
   
2. Average frame noise
   
3. Average number of sources extracted per frame
   

1. Average Frame-frame offsets and dispersions
   
2. Array rotations
3. Band-band and R1 vs. R2-R1 array registration
4. Telescope pointing (with respect to tile position)
5. Reconstructed positions of Tycho stars
6. Number and distribution of Tycho stars
7. Match rates with high density optical catalog

1. Number of 'solos' blanked
2. Image background and noise
3. Mean, maximum and dispersion in seeing
4. Number sources extracted in each band

1. Average reduced chi-squared in psf-fit for high and low SNR stars
2. Average sigma in aperture magnitudes for high and low SNR stars
3. Number of times psf was changed in scan

1. Number of R1 sources with no matching R2-R1
2. Aperture correction and magnitude (ap-psf and R1/R2) normalizations
3. Numbers of 'purged' sources per scan

1. Band-combination summary (i.e. N(JHKs), N(JH), N(J)....)
2. Average band-band position dispersions

1. Dispersion in background
2. Number of galaxy candidates
3. Number of LCSB candidates

1. Bright Planet Alert

1. Photometric zero point offset dispersion
2. Extinction coefficients
3. Sensitivity measurements (repeatability)
4. Completeness and Reliability measurements

1. Photometric offsets in scan overlaps
2. Positional offsets in scan overlaps
3. Image background offsets in scan overlaps

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.