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VII. 3-Band Cryo Data Release

4. Atlas and Source Working Database Preparation


  1. Scope and Scan Selection
  2. Tile Selection
  3. Frameset and Frame Selection
  4. Duplicate Source Identification
  5. All-Sky Release Catalog Association

Preparation of the 3-Band Cryo and Source Working Database follows the general steps of the Final Product Generation (FPG) processing that were used for the All-Sky Data Release, as described in V.1. The scope of the 3-Band Cryo data to be included is first defined. Then the input data set to be used for Multiframe Pipeline processing is selected, and the set of Atlas Tiles are selected for which Single-exposure images are to be coadded and sources extracted. The most significant difference in FPG for the 3-Band Cryo is that primary extracted source product is the full Source Working Database produced from Multiframe Pipeline processing, rather than a highly reliable, vetted Catalog, as was the case for the All-Sky Release.

To facilitate best use of the 3-Band Cryo Source Working Database, the entries were positionally cross-correlated with the All-Sky Release Source Catalog as part of FPG, and the associated Catalog source information is added to the 3-Band Cryo WDB record. This association step is described in section VII.4.e below.

a. Scope and Scan Selection

The WISE 3-Band Cryo Data Release includes data acquired during the 3-Band Cryo survey phase, 6 August 2010 to 29 September 2010 UTC, while the inner payload cryogen tanks held solid hydrogen. During this time, WISE conducted 1,643 survey scans, 07101b to 08744a, and collected 392,879 framesets of image data. WISE obtained multiple, independent exposures of the sky in two broad ecliptic longitude bands covering 42.2°<λ<98.0° and 228.5°<λ<281.7° during the 3-Band Cryo phase. The nominal frame depth-of-coverage accumulated during the 3-Band Cryo phase is encoded by the different colors in Figure 1.

The 3-Band Cryo Single-exposure Images and Single-Exposure Source Database contain the calibrated image sets and extracted source lists from all 392,879 of the framesets contained in the 1,643 scans performed during the 3-Band Cryo survey phase.

Figure 1 - Ecliptic sky plot showing the average raw frameset depth-of-coverage for the WISE 3-Band Cryo survey period in 23'x23' spatial bins. The key on the left side of the image indicates the depth of coverage encoded by each color, and in parenthesis, the cumulative area (in square degrees) having that coverage or greater.

b. Tile Selection

The 3-Band Cryo Release includes 5,649 Atlas Tiles for the purpose of coadding Single-exposure images and extracting sources in Multiframe Pipeline processing.

The selected Tiles are the subset of the 18,240 Atlas Tiles that tesselate the sky that have at least 25% of their area covered by more than four 3-Band Cryo Single-exposure images in any one band. Coverage statistics were averages computed in 15'x15' spatial bins so the precise >4-deep coverage within a Tile may be less than 25%. In addition, the coverage statistics were computed using only nominal frame quality scores, but not the dynamic frame filtering that is done in the coadd module in the Multiframe Pipeline.

The names (coadd_id) and position information for the Atlas Tiles that comprise the 3-Band Cryo Data Release Atlas and Catalog are listed in Table 1.

Table 1 - Atlas Tiles Included in the 3-Band Cryo Release

c. Frameset and Frame Selection

Not all of the 392,879 individual framesets acquired during the 3-Band Cryo survey phase were used in the Multiframe processing. Framesets, and in some cases individual band-frames were used for image coaddition and source extraction only if they satisfied minimum quality requirements for the survey. Frameset and frame exclusion was done both as a static filtering of the inputs to the Multiframe Pipeline, and as dynamic frame filtering in the coaddition process.

Framesets and/or band-frames were filtered out of the inputs to the Multiframe Pipeline (i.e. static filtering) in the following cases:

Dynamic frame rejection was carried out in the image coaddition subsystem ( during 3-Band Cryo Multiframe processing. This filtering identified and excluded image frames that contain a large number of aberrant pixels as tagged in the Single-exposure Bit Masks. Frames were rejected if they are heavily contaminated by scattered moonlight, large numbers of saturated pixels, or large numbers of glitches and cosmic rays.

The total number of frames that contributed to the full set of coadded 3-Band Cryo Release Atlas Images in each band is listed in Table 2. The frame count differs between bands because some of the static and all of the dynamic frame filtering was band-dependent. Approximately 97%, 96% and 87% of the frames acquired during the WISE 3-Band Cryo survey phase were included in the construction of the Image Atlas and Source Database in W1, W2 and W3, respectively.

Table 2 - Number of Frames Used in Multiframe Processing for the 3-Band Cryo Sky Data Release
BandNumber of Frames

In addition to the frameset and frame-level filtering, pixel-level outlier rejection was performed during the Multiframe Pipeline coaddition process. Pixel outlier rejection affects the coverage on smaller scales in the resulting Atlas Images that can be tracked by their corresponding Depth-of-Coverage Maps. The coverage that was available for the measurement of each Catalog source is tabulated in the Source Working Database w1m, w2m and w3m columns. A detailed discussion of the 3-Band Cryo sky coverage is given in VII.5.a.

The achieved depth-of-coverage in each band after static and dynamic frameset and frame filters, and pixel-level outlier rejection in the Multiframe processing is shown in Figure 2. The gap in W3 coverage due to the inadvertent W3 saturation is clearly visible. Note that the horizontal bands of low coverage caused by magnetic torque rod enabling in the All Sky Release, shown in Figure 2 in V.2 are partially filled in by the 3-Band Cryo observations. These gaps were completely filled with W1 and W2 exposures during the Post-Cryo observations.

Framesets that contribute to each Atlas Image are tracked in the 3-Band Cryo Release Atlas Image Frame Cross-Reference Table. This table contains a listing of frameset identifiers that correspond to each Atlas Tile in each band, and can be used to determine which framesets were used to construct a particular Atlas Image, or to determine to which Atlas Images a particular frameset or frame contributed.

Figure 2 - Net Coverage in the W1, W2 and W3 bands for the WISE 3-Band Cryo Data Release. Colors encode the average frame depth-of-coverage in 14'x14' spatial bins as indicated by the legends on the left.

d. Duplicate Source Identification

The WSDS Multiframe Pipeline combines multiple Single-Exposure Images that fall within the footprint of predefined 1.56°x1.56° Atlas Tiles to construct the coadded Atlas Images and extracted Source Working Database. Atlas Tiles overlap by 180" in Declination and Right Ascension on the celestial equator. The RA overlap increases towards the equatorial poles. Source that fall within the Tile overlap region may be detected during Multiframe processing for each Tile, and thus appear multiple times in the L3 WDB. These detections are redundant because the same Single-exposure frame images contribute to each overlapping Tile. The duplicate resolution process that selected one unique apparition of duplicate detections for the All-Sky Release Source Catalog on the basis of pure geometric criteria is described in V.3.c.

The WISE 3-Band Cryo Source WDB contains redundant detections of objects that fall in the 3-Band Cryo Atlas Tile overlap regions. The same duplicate resolution processing used for the All-Sky Catalog was applied to the 3-Band Cryo Source WDB. The use_src parameter has been added to 3-Band Cryo WDB records to enable selecting only one apparition of redundant detections.

The use_src parameter is a one-digit integer that identifies 3-Band Cryo Source WDB entries that are either single, unique detections of sources, or members of redundant extraction groups that are selected to be the "best" member of the group according to the criteria described in V.3.c.

Select WDB entries that have use_src=1 to avoid duplicate, redundant detections of the same object.

Two other parameters that are included in the 3-Band Cryo WDB provide additional information about redundant detections.

e. All-Sky Release Catalog Associations

WISE All-Sky Release Source Catalog and Atlas are the best compendia of sources of mid-infrared radiation for the full-sky. Because the WISE 3-Band Cryo observations provided independent, second-epoch observations for 30% of the sky, the 3-Band Cryo Source Working Database and Atlas are best used as resources to learn more about objects that are found in the All-Sky Release products. To facilitate this, entries in the 3-Band Cryo Source WDB have been positionally cross-correlated with the All-Sky Release Catalog to find counterparts within 3 arcseconds of the 3-Band Cryo source position.

Included in the 3-Band Cryo WDB records are:

The All-Sky Catalog association process and information provided is analogous to that provided for associations with the 2MASS Point Source Catalog (IV.7).

Last update: 2012 July 26

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