IV. 2MASS Data Processing

10. Quality Assurance

a. Overview

Quality Assurance is the final analysis ensuring that the 2MASS data are meeting Level 1 specifications. It closes the loop with the observatory by determining which of the tiles can be forever checked off as ``done'' and which need high or low priority re-scans. It also informs the database team at IPAC of which scans have sufficient quality to be loaded into the working 2MASS database.

b. Steps in Quality Assurance

There are two steps in Quality Assurance (hereafter "QA"). The first step is referred to as "24-hr QA" and is a quick check of the data within 24 hours after the data tape reaches IPAC. The second step is referred to as "Nightly Science QA" and is the comprehensive check of the data performed after the night is fully processed. Both of these steps are described in more detail below.

i. 24-hr QA

The 24-hr QA report is generated after a night's data tape has reached IPAC. In this quick processing, only the darks, responsivities, and calibration scans are generally run. The 24-hr QA report checks that the telescope pointing, scanning, and focus are within tolerance. The report also checks that the intrument is behaving as expected by checking that the darks and responsivities are within nominal limits. The 24-hr QA report further determines whether with default processing the night is photometric or not. This pre-processing allows us to see if any overrides will be needed in full production processing, and if the night appears to be a disaster photometrically, we can triage the night at this step and not schedule it for full production processing. The observatory can also be immediately notified that these tiles need to be re-observed.

ii. Nightly Science QA

The Nightly Science QA report shows the quality parameters generated by each subsystem in the data processing pipeline. In this processing, all of the data are run with the exception of any scans triaged at the 24-hr step. The report generates an overall review of the night; scan-by-scan quality reports on telescope tracking and stepping, background/seeing/focus, astrometry, photometricity, and extended source processing; and a report on the preliminary quality scores for each scan. Diagnostic images and plots are also generated.

The quality reviewer uses the preliminary scores generated above as a baseline, then checks the quality reports along with the diagnostic images and plots to assign final scores to each scan. The final scores are then justified in a report which is mailed to UMass. UMass reviews the report, agrees with the recommendation or requests slight changes to the scoring, and then IPAC generates transaction files which (a) notify the observatory of the scores for each scan so it can prioritize any re-scanning that needs to be done and (b) which notify the database team at IPAC of scans that have sufficient quality to load into the working database.

Scans are given quality scores from 0 (scans that need immediate re-scanning) to 10 (scans that meet all Level 1 specifications). The recipe used by the reviewers to determine the quality of each individual scan is as follows: In general, each scan is scored using a base quality number multiplied by two individual quality factors (score = base * photometric factor * sensitivity factor), as detailed below.

However, there are several other checks performed on the data which can result in a scan being given a lower quality score than that computed from the formulae above. Any scans with problems like those mentioned below are not included in our working database, our intent being to re-scan them again later:

QUALITY = 0: First priority for re-scanning

QUALITY = 1: Second priority for re-scanning

QUALITY = 2: Third priority for re-scanning

Scans with final quality scores of 3 or greater are loaded into the 2MASS working database. These quality scores have been used as one of the primary criteria in deciding which scans are included in the final release of data to the astronomical community. (See Section
II.1 for full details.) For those interested in these final scan-by-scan scores, they are kept in the Survey Scan Information Table, under the column name "quality".

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