III. NEOWISE Single-exposure Images

III.1. General Properties

III.1.a. Description and Format

The Final NEOWISE Data Release brings to 26,888,166 the total number of NEOWISE Single-exposure image sets available. These were produced using improved calibrations and data processing algorithms than those used to support earlier WISE releases (section IV.1.b).

Each Single-exposure image set consists of three 1016 x 1016 pixel images @ 2.75"/pix formatted in the Flexible Image Transport System (FITS). The FITS headers contain World Coordinate System (WCS) information following the standard for astronomical image data with field-of-view distortion represented in the "Simple Imaging Polynomial" (SIP) format. See section III.1.b for an example header.

The three elements of each image set are:

Intensity images - Two images, one in the W1 and W2 bands, that contain the calibrated sky images for each individual 7.7 sec W1 and W2 exposure. Instrumental calibrations have been applied to these images to remove instrumental signatures. The FITS headers contain photometric zero points and full WCS information.

Uncertainty maps - Two images, one in the W1 and W2 bands, that give the 1-σ uncertainty estimate for each pixel in the corresponding intensity images. These maps provide the instrumental noise component for photometric uncertainty estimates.

Bit-masks - Two images, one in the W1 and W2 bands, that provide information about the status of each pixel in the single-exposure intensity images.

Section III.3 provides advice on how to use these products.

The single-exposure image products have the following generic filenames:

Intensity image: frameID-wBAND-int-1b.fits

Uncertainty image: frameID-wBAND-unc-1b.fits

Bit-Masks: frameID-wBAND-msk-1b.fits

where BAND = 1 or 2 and frameID is a unique identification string pertaining to the image set. frameID has the form SSSSxMMM, where SSSSSx is the identifier of the scan in which the frameset was taken, scan_id, and MMM is the frame number, frame_num, within the scan. BAND and frameID are variables that match the values of keywords with the same name in FITS headers. The WISE Single-exposure Image FITS header content is described in III.1.b.

The Single-exposure (L1) Image Metadata Table provides additional information about the WISE Single-exposure image sets including much of the image header content and derived statistical and quality assessment information pertaining to both the Single-exposure images and extracted source database. This metadata table can be searched using the IRSA Catalog Query Engine.

CAUTION: The NEOWISE single-exposure image archive contains all images in the scans that are part of the NEOWISE Data Release scope (section I.3), regardless of their quality. Many of these framesets suffer from the following problems:

Degraded image quality due to spacecraft jitter and bad tracking during exposures

Contamination by severe scattered light artifacts from the moon and bright planets

Contamination by bright satellite streaks both on and off the FOV

Contamination by large numbers of cosmic ray strikes because they were taken while the spacecraft was passing through the South Atlantic Anomaly (SAA)

Contamination by electronic noise signatures.

Example images showing some of these problems can be seen in section III.2, the Single-exposure Cautionary Notes.

You can identify single-exposure image sets that are of good quality using several of the keywords in the FITS headers and/or values in the metadata tables as follows:

qual_fact > 0 - Good overall quality score (includes image quality and pixel noise levels; available in the Frame Metadata and Image Inventory Tables only)

SAA_SEP (saa_sep) > 0 - Outside of the nominal boundaries of the South Atlantic Anomaly

MOON_SEP (moon_sep) > 24° - Beyond the worst of the scattered moonlight (use larger values to be more conservative)

III. NEOWISE Single-exposure Images

III.1. General Properties

III.1.a. Description and Format

III.1.b. Single-exposure Image Header Descriptions

III.1.c. Single-exposure Image Metadata Column Descriptions

III.1.d. Single-exposure Image Inventory Table Column Descriptions