Appendix 3. Long Exposure (6x) Scan Databases, Catalogs and Images

5. Data Processing

a. Modifications Relative to Final Survey Processing

Reduction of the 2MASS Long Exposure (6x) scan data was carried out using a minimally modified version of the 2MASS Automated Production Pipeline (2MAPPS v3.0) that was used for final processing of all of the primary survey data (see IV.1). The basic processing steps shown in Figure 1 of IV.1 remained unchanged from the final survey processing, and the pipeline output products from 6x processing were very similar in form to those from the survey data processing.

The modifications to 2MAPPS for the 6x processing fell into three categories and priorities. Highest priority was given to the fundamental changes that were necessary so that the 6x data would successfully process without software failures, such as corrections dealing with the longer exposure times and resulting higher sky background count levels and structure. Second priority was given to changes that fixed software bugs that were known to exist 2MAPPS v3.0, or that were discovered since the release of the All-Sky Catalogs. Finally, modifications to the software and/or the quality assurance process that further improved data quality and brought output data formats closer to those of the release products were made as time and resources permitted.

Brief summaries of the major modifications made to each of the data reduction subsystems are given below. A link to the pertinent section of the main survey supplement is given for each subsystem. Further descriptions of the changes made to the astrometric and photometric calibration procedures, extended source processing and artifact identification for the 6x data are given in Sections A3.5.b, A3.5.c, A3.5.d, and A3.5.e, respectively.

As with the main survey, 6x data processing was done in two steps. Preliminary processing was carried out shortly after the 6x observations were made using a 2MAPPS version that was modified only to accommodate the longer exposure times of the 6x data. The results of the preliminary reduction were used to assess the basic 6x data quality for observatory support and to prepare for the final processing. Final 6x data processing was carried out as part of the 2MASS Extended Mission, and incorporated best practices learned from the survey itself, as well as analysis of the preliminary 6x processing results. Because final 6x processing followed the release of the final survey data products, it was possible to incorporate Quality Assurance steps that compared the 6x products to the well-characterized All-Sky Catalogs and Images.

i. Synopsis of Reduction Pipeline Changes By Subsystem

Instrumental Calibration (IV.2)

Atlas Image Generation (IV.3)

Point Source Photometry (IV.4.b)

Position Reconstruction (IV.6)

Optical Associations (IV.4.f)

Extended Source Processing (IV.5)

Artifact Identification (IV.7)

Photometric Calibration (IV.8)

Quality Assurance (IV.10)

[Last Updated: 2007 January 8; by R. Cutri]

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