Data processing for 2MASS was conducted using the highly automated 2MASS
Production Processing System (2MAPPS) which converted each night's raw
imaging data from each telescope into calibrated images and extracted source
lists.
Processing was done in two stages. Preliminary processing
was carried out while the Survey was ongoing using a version of
2MAPPS (v2.x) that was allowed to evolve and improve
continuously as our knowledge
of the telescopes, cameras, detectors, atmosphere and the near infrared sky
improved. The 2MASS Sampler, First and Second Incremental Data Releases
were derived from the results of the preliminary data processing. A second,
complete reprocessing of all Survey data following the completion of the
Survey observations was performed, and enabled all data to be reduced
using a single, stable software platform, 2MAPPS v3.0. 2MAPPS v3.0
incorporated lessons learned during the preliminary processing and feedback
provided by users of the Incremental Data Release products. It also made
use of reference datasets not available earlier, such as the Tycho 2
astrometric reference catalog, and information gathered from analysis of
the complete survey data set. 2MAPPS v3.0 also contained numerous upgrades
that improved the general quality and yield of data from the survey. Finally,
2MAPPS v3.0 included more extensive Quality Assurance tied explicitly to
metrics derived from scientific investigations of the data.
An overview of the basic processing steps are given below in
Section b, and a summary of the improvements incorporated into
2MAPPS v3.0 for final data processing are given in Section c.
Sections IV.2-10 provide a detailed description of data processing
algorithms and results.
Approximately 17 GB of raw digital image data were acquired each clear night
at the 2MASS observatories. These data were written to DLT
tape (one tape per observatory per night) and transported to the
Infrared Processing and Analysis Center (IPAC).
At IPAC,
the observatory data tapes were read and validated, and the data were reduced
using the 2MASS Production
Processing System (2MAPPS). 2MAPPS was designed to exploit the Survey's
innovative data acquisition techniques
to produce image, point and extended source data.
The 2MAPPS High Level Flowchart (Figure 1)
illustrates the basic components of the 2MAPPS system.
Data from one night and one observatory were processed as a unit.
For each telescope-night, each 1° calibration or 6° survey scan
was processed individually, with
the J, H and Ks frame data in each scan processed in parallel.
Scan data processing within 2MAPPS was a linear process with the
output of each step being the input for each subsequent step.
Iterations were held to a minimum for efficiency.
a. Data Processing Strategy
b. Nightly Data Processing Steps
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| Figure 1 |
The basic scan processing steps are the same for calibration and survey scans, and are as follows:
Once all scan processing for data taken at one observatory in one night is completed, post-scan-processing is carried out. The nightly post-scan-processing steps include:
Pipeline processing yields lists of band-merged, photometrically and astrometrically calibrated point and extended source "detections" from each Survey and Calibration scan. These lists are accumulated into the Point Source and Extended Source Working Databases from which the 2MASS Point and Extended Source Catalogs are drawn. The process of generating the Catalogs from the Working Databases is described in Section V.
Final 2MASS Survey data processing using 2MAPPS v3.0 began on 2 August 2001 and was completed on 6 February 2002. All Survey data acquired under photometric conditions were included in the final processing. This included scans of 70,712 Tiles taken on 1415 survey nights (691 northern and 750 southern) spanning 7 June 1997 UT to 15 February 2001 UT. The final processing Working Databases contain 1,314,981,867 Point and 2,590,500 Extended source extractions, and an Atlas of 4,879,128 calibrated FITS images
The following list summarizes the major improvements relative
to earlier versions that were incorporated
in 2MAPPS v3.0. Because of these improvements, the quality of
the 2MASS All-Sky Release data products surpass those
from the Incremental Releases, and the All-Sky products are
designed to supersede the products from the earlier releases.
[Last Update: 10 March 2003, by R. Cutri]
c. Improvements Incorporated in Final Processing (2MAPPS v3.0)
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