I. Introduction

1. Mission Overview

Contents

a. WISE
b. NEOWISE
c. WISE At-A-Glance
d. WISE Data Releases

i. The All-Sky Data Release
ii. The WISE 3-Band Cryo Data Release
iii. The NEOWISE Post-Cryo Data Release
iv. The AllWISE Data Release
v. The WISE Preliminary Data Release
vi. The NEOWISE Post-Cryo Preliminary Data Release

e. About this Document

a. WISE

The Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010, AJ, 140, 1868) is a NASA Medium Class Explorer mission that conducted a digital imaging survey of the entire sky in the 3.4, 4.6, 12 and 22 μm mid-infrared bandpasses (hereafter W1, W2, W3 and W4). WISE produced and released to the world astronomical and educational communities and general public a digital Image Atlas covering the sky in the four survey bands, and a reliable Source Catalog containing accurate photometry and astrometry for over 500 million objects. The WISE Catalog and Atlas enable a broad variety of research efforts ranging from the search for the closest stars and brown dwarfs to the most luminous galaxies in the Universe. WISE science data products serve as an important reference data set for planning observations and interpreting data obtained with future ground and space-borne observatories, such as JWST.

WISE conducted its survey using a 40 cm cryogenically-cooled telescope equipped with a camera containing four mid-infrared focal plane array detectors that simultaneously imaged the same 47x47 arcmin field-of-view on the sky (Figure 1). The spacecraft flew in a 526x531 km x 97.5°, 6pm ascending node, sun-synchronous polar orbit. The WISE telescope scanned continuously at near constant Ecliptic longitudes while a scan mirror temporarily froze the sky on the focal planes. Sets of exposures (7.7 sec in W1 and W2 and 8.8 sec in W3 and W4) were acquired at each point on the sky as the telescope scanned from pole-to-pole. The FOV of each successive exposure set overlaps the previous one by 10%, and the scan paths of adjacent orbits overlap by approximately 90% on the Ecliptic because of the WISE orbital precession. The number of independent exposures accumulated on each point on the sky was typically 12 or more on the Ecliptic plane and increases to several hundred at the Ecliptic poles.

WISE was launched on a Delta II 7320 rocket from Space Launch Complex 2 at Vandenberg Air Force Base at 14:09:33 UTC on December 14, 2009 (Figure 2). The cryogenic telescope cover was ejected on December 29, 2009, two weeks into the in-orbit checkout (IOC) period (Figure 3). Survey observations were started at 01:45:14.1 UTC on January 7, 2010 following the successful completion of the IOC. Full, 4-Band Cryogenic survey operations continued uninterrupted until August 6, 2010 when the solid hydrogen in the outer cryogen tank was exhausted. WISE surveyed the sky approximately 1.2 times during the full cryogenic phase. WISE continued to survey another 30% of the sky in the 3-Band Cryo phase using the 3.4, 4.6 and 12 μm detectors until September 29, 2010 when the last of the solid hydrogen cryogen in the inner tank sublimated. After cryogen exhaustion, the two short wavelength detectors remained operational at near cryogenic survey sensitivity. WISE continued to survey the sky through February 1, 2011 in the NEOWISE Post-Cryo mission phase to complete the coverage of the inner edge of the main asteroid belt. Data collection with WISE was halted after acquisition of the final Post-Cryo survey image at 11:03:01.3 UTC on February 1, 2011 (Figure 4). Final contact with the WISE flight system was made on February 17, 2011. WISE remains in orbit, hibernating in an inertial pointing mode with the telescope at right angles to the Sun.

During its 413 day IOC and operational phase, WISE orbited the Earth 6240 times, collecting 2.7 million exposures containing 7.9 trillion pixels of information. 15.6 TB (8.6 TB compressed) of image and engineering data were transmitted to the ground via the TDRSS network, and ingested and processed to produce calibrated image and extracted source data products. No survey time was lost due to unplanned safe holds or other unexpected behavior, and fewer than 100 image frames were lost due to downlink errors.

Prof. Edward Wright of the University of California Los Angeles is the WISE Principal Investigator. The WISE program is overseen by the NASA Explorer Office at Goddard Space Flight Center. Overall project management, project science and mission operations is the responsibility of the Jet Propulsion Laboratory, California Institute of Technology. Ball Aerospace and Technologies Corporation is the prime contractor for the WISE spacecraft, and managed the Integration and Test for the program. The Space Dynamics Laboratory at Utah State University is the prime contractor for the WISE payload that includes the cyrogenic telescope, optics and detector assemblies. The Infrared Processing and Analysis Center at Caltech is responsible for WISE data ingest, processing, archiving and distribution to the user community. Education and Public Outreach for WISE is conducted by the University of California Berkeley. Funding for the WISE mission is provided by the Astrophysics Division of NASA's Science Mission Directorate.

Figure 1 - WISE flight system inside one-half of the fairing on the Delta II rocket at Vandenberg AFB. The domed telescope cover was ejected two weeks after launch.	Figure 2 - WISE launch from Vandenberg AFB at 14:09:33 12/14/09 UTC (credit: United Launch Alliance)
Figure 3 - WISE "first-light" image taken on 12/31/10 during IOC. This is a four-band color composite image showing a region in the constellation Carina.	Figure 4 - WISE "last-light" image taken on 2/1/2011. This is two-band color composite image showing a region in the constellation Perseus.

b. NEOWISE

NEOWISE (Mainzer et al. 2011 ApJ, 731, 53) is an enhancement to the primary WISE mission data processing and archive system, funded by the NASA Science Mission Directorate's Planetary Science Division, that enhances the Solar System science return of WISE data. Dr. Amanda Mainzer of the Jet Propulsion Laboratory, California Institute of Technology is the NEOWISE Principal Investigator. The NEOWISE program consists of two parts. The first component, the WISE Moving Object Pipeline System (WMOPS), exploits the WISE observing cadence that images repeatedly the same region of sky to detect and characterize moving solar system objects, with special emphasis on the search for Near Earth Objects. The second component of NEOWISE provides an archive of image and source data from individual WISE exposures to enable pre-covery of WISE detections of objects that are discovered after the end of the WISE mission.

NEOWISE/WMOPS is a software system that links non-inertial detections made on the single-exposure WISE images made near the same point on the sky to form candidate moving object tracklets (Figure 5). WMOPS reported candidate tracklets to the IAU Minor Planet Center (MPC) within 10 days of the midpoint of the WISE observations. The MPC computed initial orbits and posted objects on their websites for follow-up and confirmation by ground-based observers. The first tracklet was reported to the MPC on January 9, 2010. Since then, over 279,000 tracklets were reported, and nearly two million individual vetted WISE mid-infrared detections of over 158,000 unique small bodies are available from the MPC. WISE/NEOWISE has been credited with the discovery 135 previously unknown NEOs, 20 comets (Figure 6), and over 30,000 main belt asteroids.

The archive component of the NEOWISE program provides for the release of WISE single-exposure images and extracted source working database to the science community in conjunction with the WISE primary mission data releases. These products are accessed via the on-line services of the NASA/IPAC Infrared Science Archive (IRSA). This enhancement also provides a query capability to the IRSA services to enable searching for WISE single-exposure images that cover the predicted position of a moving object, or source detections from the single-exposure images that are in proximity to predicted positions of moving objects using the object name or orbital elements.

The NASA Planetary Division also funded the NEOWISE Post-Cryo survey phase to enable the continuation of the WISE Moving Object search.

Figure 5 - WISE 4-band color-composite of the Tadpole Nebula illustrating moving object tracklets. This image was formed by combining multiple independent WISE exposures of the region without pixel outlier rejection, so that moving objects appear multiple times. The rectangles outline the tracklets produced by asteroids 1719 Jens and 1992 UZ5. The circled streak near the top of the image is a residual trail left by a satellite detected in one of the WISE exposures.

Figure 6 - Montage of the 20 comets that were either discovered by the NEOWISE program, or for which the WISE observations revealed their activity. These are 3-band (4.6-12-22μm) color composite images formed by coadding many independent exposures on the position of the comets.

c. WISE At-A-Glance

d. WISE Data Releases

i. The All-Sky Data Release

The WISE All-Sky Data Release includes data from the full cryogenic mission phase, taken between January 7 and August 6, 2010, and covers >99% of the sky. The All-Sky Release image and extracted source data products were generated from a complete second-pass processing of the full cryogenic survey data set. The second-pass processing used an updated version of the WISE Science Data System (WSDS) that incorporated improved calibrations and processing algorithms developed from analysis of the full mission data set, and corrections to deficiencies in first-pass processing.

While the All-Sky Release products reflect the best available calibrations and data reduction algorithms, they are known to contain a number of features and limitations. Users are strongly encouraged to review the Cautionary Notes section of the Explanatory Supplement to best exploit the products in your research.

The All-Sky Data Release products supersede the products from the April 2011 Preliminary Data Release. Whenever possible, All-Sky Release image and extracted source products should be used instead of those from the Preliminary release.

ii. The WISE 3-Band Cryo Data Release

The WISE 3-Band Cryo Data Release contains W1, W2 and W3 image and extracted source data that were acquired following the exhaustion of solid hydrogen in the satellite's payload outer cryogen tank. WISE surveyed 30% of the sky between 6 August and 29 September 2010 UTC while the detectors continued to be cooled by the hydrogen ice in the inner cryogen tank. During the 3-Band Cryo survey phase, the W1 and W2 detectors operated with nearly the same sensitivity as during the 4-band cryogenic survey. Higher operating temperatures and elevated thermal emission from the warming telescope reduced the sensitivity of the W3 measurements and fully saturated the W4 detector.

The 3-Band Cryo Release images and extracted source data were generated from second-pass of the 3-Band Cryo data that incorporated all improvements realized for the All-Sky Data Release processing, along with modifications that were necessary for the special characteristics of the 3-Band Cryo data.

The 3-Band Cryo survey, contents and cautionary notes for the release products, and data processing modifications are described in Section VII of this Explanatory Supplement.

iii. The NEOWISE Post-Cryo Data Release

The 2013 NEOWISE Post-Cryo Data Release contains W1 and W2 Single-exposure image and extracted source data that were acquired following the exhaustion of solid hydrogen in the both inner and outer cryogen tanks. WISE surveyed 70% of the sky between 29 September 2010 and 1 February 2011 UTC while the telescope and focal plane assemblies warmed to 73.5 K. During the Post-Cryo survey phase, the W1 and W2 detectors continued to operate with nearly the same sensitivity as during the 4-band cryogenic survey, but the W3 and W4 detectors were fully saturated.

The Post-Cryo Release products were generated from second-pass data processing that utilized improved calibrations and reduction algorithms tuned specifically for the performance of the warmer detectors and telescope during the Post-Cryo survey phase. These products provide the best individual flux measurements for solar system objects that were identified by WMOPS during the Post-Cryo survey phase, and they enable follow-up of inertial sources found in the WISE All-Sky Release Catalog to investigate time-dependent properties such as flux variability and proper motion. The Post-Cryo Release does not include coadded Atlas Images or a deep source detection Working Database like the All-Sky and 3-Band Cryo Releases.

Post-Cryo survey operations, the contents and cautionary notes for the Release data products, and data processing are described in Section VIII of this Explanatory Supplement.

iv. The AllWISE Data Release

Data from the WISE Full Cryogenic, 3-Band Cryo and NEOWISE Post-Cryo survey phases were combined to generate the products for the AllWISE Data Release that was made on 13 November 2013.

WISE surveyed the sky more than two complete times during the three survey periods. The W1 and W2 Single-exposure images from all phases and the W3 and W4 images from the full cryogenic phase were coadded to generate an enhanced Image Atlas and Source Catalog. The enhanced images and source extractions probe approximately 0.4 mags deeper at the short wavelengths than the All-Sky Release Atlas and Catalog in unconfused regions, and have improved coverage in areas that were adversely affected by the moon in the individual phases. AllWISE also exploits the multiple survey coverage epochs by measuring apparent motions for the Catalog sources, and by compiling a Multi-epoch database of "forced" profile-fit photometry of each deep Catalog source on all of the individual Single-exposure images.

The user's guide to the AllWISE data products, their cautionary notes, and updates to the data processing made for their production are described in the Explanatory Supplement to AllWISE Data Release Products.

v. The WISE Preliminary Data Release

The WISE Preliminary Data Release was the first release of a large quantity of WISE image and extracted source data to the scientific and educational community. The Preliminary Release included data from the first 105 days of the WISE full cryogenic survey and covered approximately 57% of the sky. The goal of this early release was to provide a significant data set to the scientific community as quickly as possible following the end of mission operations to introduce users to the WISE data and to enable a broad range of investigations. The Preliminary Data Release also enabled the WISE Project Team to exercise and refine data preparation and release processes prior to the All-Sky Release.

The Preliminary Release products were generated from the results of first-pass WISE data processing that started just three months following the survey start. Processing was done with an early version of the WSDS that was based on pre-launch and very early survey calibrations and reduction algorithms. Detection thresholds and source selection criteria for the Preliminary Release Source Catalog were conservative with the emphasis put upon providing a reliable yet representative sample of WISE data. As a result of the rapid deployment necessary to meet the schedule for the Preliminary Data Release, the Preliminary Release products did not benefit from much of the experience gained over the full mission lifetime. Consequently, the Preliminary Release products contain a number of known features and limitations that are documented in the Preliminary Release Explanatory Supplement.

The Preliminary Data Release products are superseded by the products from the WISE All-Sky Data Release.

vi. The NEOWISE Post-Cryo Preliminary Data Release

The NEOWISE Post-Cryo Preliminary Data Release made on July 31, 2012 contains W1 and W2 Single-exposure image and extracted source data that were acquired during the Post-Cryo survey phase following the exhaustion of solid hydrogen in the both inner and outer cryogen tanks.

The Post-Cryo Preliminary Release products were generated from first-pass WISE data processing that utilized early calibrations and reduction algorithms that were not optimized for the performance of the warm system. The early processing provided quality assessment to support survey operations and input for the WMOPS that identified and reported candidate moving object tracklets to the MPC within 10 days of their observation for timely ground-based recovery and confirmation. The Post-Cryo Preliminary Release products did not receive the same level of scrutiny as the cryogenic mission data products.

The Post-Cryo Preliminary Data Release products are superseded by the products from the 2013 Post-Cryo Data Release.

Data products, processing algorithms and cautionary notes for the Post-Cryo Preliminary Release are integrated in Section VIII of this Explanatory Supplement, along with general descriptions of the Post-Cryo survey operations and the 2013 Post-Cryo Release.

e. About this Document

This Explanatory Supplement provides users of WISE products with a description of the overall WISE survey and data products. An executive summary of the All-Sky Data Release products is available in Section I.2, and known features and limitations in Section I.4. Section II contains a more detailed user's guide to the products, with information about their content and characteristics. In Section III, the WISE flight system, operations and survey strategy are presented. Detailed descriptions of the functions and algorithms of the WSDS are described in Section IV. Generation of the All-Sky Image Atlas and Source Catalog are described in Section V, and detailed descriptions of the achieved performance and quality of the All-Sky Release data products are presented in Section VI.

Section VII contains the description of the 3-Band Cryo Data Release products and data processing.

Section VIII contains the description of the Post-Cryo survey phase operations, data processing and the 2013 Post-Cryo and Post-Cryo Preliminary Data Release products.

This Explanatory Supplement is a living document that will be updated frequently to provide the most current information for users of the WISE data products. Please see the Document Change History for a record of the latest updates.

Last update: 2017 May 11