II. User's Guide to the WISE Preliminary Data Release

• A - Asteroid, numbered
• U - Asteroid, unnumbered
• C - Comet, periodic
• N - Comet, non-periodic
• P - Planet
• S - Planetary Satellite
• X - Unknown

Scan_id is a six character string that identifies a block of survey exposures that are acquired between two flight system maneuvers, such as reorientation of the instrument boresite near the ecliptic poles, or slews to acquire TDRSS for data downlink contacts. Because maneuvers often take place near the ecliptic poles, the scan number is roughly associated with a half-orbit's worth of images. However, scans can cover less or more than half of the arc between ecliptic poles.

The scan_id has the general form SSSSSx, where

• SSSSS is a zero-filled, five-digit integer that is twice the WISE orbit number. The orbit number increments each time the flight system passes the north ecliptic pole (NEP). Orbit number 1 was defined to start with the fictitious NEP passage immediately prior to WISE launch.
• x   is a letter assigned based on sequential count of scans started in a specific half-orbit. The first scan has x="a", the next x="b", up to a maximum of x="d" for scans in the Preliminary Release.

The first scan whose data are used in the Preliminary Data Release is scan 00936a. This was the first scan after the NEP crossing in the 468th WISE orbit. The final scan included in the Release is 04125a, the first scan after the SEP crossing in the 2062nd WISE orbit.

Frame_num has the general form MMM, a zero-filled three-digit number.

The frameset number is computed based on time bins which count from the scan start time:

where

• int[] means truncate to an integer
• frame_utc is the nominal frame exposure center UTC (when the boresite crosses the image center) in seconds
• dt_beg is 4.4s. This is a nominal offset to approximate when the exposure began
• scan_start_utc is the scan start time in seconds
• bin_size is 10s.

For example, a frame with a start time 1234 secs after the scan start time would have a frame number of 124.

N.B.

• Frame_num is not a frameset sequence number
• As a result of using a 10 sec bin, every 11th frame skips a number, so it is normal to see breaks in the frame numbering and it doesn't indicate missing data.
• Because frameset numbering is based on the predicted scan start time from the survey plan, and because frameset data may not start being acquired until well after the start of the scan, frameset numbers often do not start at 1 for a scan.

CAUTION: A spatial association between the predicted SSO position and the position of a WISE Single-exposure extraction does not necessarily mean that this is a WISE detection of the SSO. The Single-exposure Source Database contains a significant number of spurious detections of noise excursions, transient pixel events and image artifacts. Thus the spatial coincidence between the SSO position and WISE extraction may be a chance alignment with a spurious extraction or an inertial background astrophysical source. See IV.3.e.iv.1 for suggestions for identifying spurious associations.

This column is "null" if there is not a WISE Single-exposure extraction spatially associated with the predicted position of the SSO.

Source_id has the general form SSSSSxMMM-IIIIII, where

• SSSSSx is the scan_id,
• MMM is the frameset number within the scan, frame_num, and
• IIIIII is the zero-filled, six-digit source number, src, within the frameset.