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IV. NEOWISE Data Processing

IV.2. Scan/Frame Pipeline Updates


IV.2.e.i. Known Solar System Object Possible Association List (KSSOPAL) Column Descriptions

The Known Solar-System Object Possible Associations List is a compendium of asteroids, comets, planets or planetary satellites, with orbits known at the time of NEOWISE data processing, that were predicted to be within the field-of-view at the time of individual NEOWISE Single-exposures. Individual objects were observed multiple times, so may have multiple entries in the list. When the predicted position of a solar system object is in proximity to a detection in the NEOWISE Single-exposures, the NEOWISE detection position and brightness information are also provided.

CAUTION: This is not a vetted list of solar system object detections. For a reliable, well-vetted list of NEOWISE solar system object detections, please use the Moving Object Tracklets. See also the tips for selecting reliable solar system object detections in II.3.c.

The following table contains brief descriptions of the parameters provided for each record in the NEOWISE Release Known Solar-System Object Possible Association List. The columns in the table are:

Column NameFormatUnitsnullsDescription 
cntr%19ld----no Unique identification number for the KSSOPAL table entry created sequentially in the order of the Archive load processing.  
objid%36s----yesSolar System Object (SSO) The identifier field may contain any combination of MPC number, object name (e.g., Ceres), and (provisional-)designation; comets and planets have no MPC numbers.

Note - The identifiers for numbered asteroids that were observed by NEOWISE prior to mjd=59500 (13 October 2021) or after mjd=59950 (6 January 2023) may contain the MPC number, object name, and the designation. (e.g., (2643) Bernhard 1973 SD). The identifiers for numbered asteroids observed between mjd=59500 and mjd=59950 will contain only the MPC number (e.g., (2643)).

 
t%1s----yes Type of Solar System object:
  • A - Asteroid, numbered
  • U - Asteroid, unnumbered
  • C - Comet, periodic
  • N - Comet, non-periodic, and Interstellar
  • P - Planet
  • S - Planetary Satellite

Note that the interstellar objects 1I/'Oumuamua 2017 U1 and 2I/Borisov 2019 Q4 were assigned a classification of t='N' for the purposes of the NEOWISE Known Solar System Object processing.

 
ra%10.6fdegyesPredicted Right Ascension (J2000) of SSO at time of NEOWISE observation.  
dec%10.6fdegyesPredicted Declination (J2000) of SSO at time of NEOWISE observation.  
mu%7.3farcsec/secyesPredicted proper motion of SSO at time of NEOWISE observation.  
theta%5.1fdegyesDirection of predicted proper motion (E of N) of SSO at time of NEOWISE observation.  
emj%4.1farcsecyesSemimajor axis of the error ellipse of the SSO predicted position.  
emn %4.1farcsecyesSemiminor axis of error ellipse of the SSO predicted position.  
erang%5.1fdegyesPosition angle of emj axis (E of N).  
rhelio%9.5fAUyesSSO heliocentric distance at the time of the NEOWISE observation.  
rtopo%9.5fAUyesSSO Topocentric (spacecraft) distance at the time of the NEOWISE observation.  
phase%7.3fdegyesSSO phase angle at the time of the NEOWISE observation.  
amag%5.2fmagyesSSO absolute magnitude.  
vmag%6.3fmagyesSSO predicted visual magnitude at the time of the NEOWISE observation.  
slope%5.2f----yesSlope parameter for computing phase-dependent term in visual mag  
perdist%10.7fAUyesSSO perihelion distance at the time of the NEOWISE observation.  
ecc%9.7f----yesSSO orbital eccentricity  
incl%12.8fdegyesSSO orbital inclination  
pv1%11.8s----yesSSO orbit P vector (unit vector of Sun toward perihelion) X component  
pv2%11.8f----yesSSO orbit P vector (unit vector of Sun toward perihelion) Y component  
pv3%11.8f----yesSSO orbit P vector (unit vector of Sun toward perihelion) Z component  
qv1%11.8f----yesSSO orbit Q vector (unit vector orthogonal to P in orbit plane, right-handed about orbital angular momentum vector) X component  
qv2%11.8f----yesSSO orbit Q vector (unit vector orthogonal to P in orbit plane, right-handed about orbital angular momentum vector) Y component  
qv3%11.8f----yesSSO orbit Q vector (unit vector orthogonal to P in orbit plane, right-handed about orbital angular momentum vector) Z component  
pertime%13.5mjdateyesSSO orbit perihelion passage time, modified Julian date  
err%4.1f----yesSSO orbital element quality estimate  
mjd%14.8fmjdateyesModified Julian date of the mid-point of the observation of the frameset within which the FOV the SSO is predicted to fall.

N.B. - The true observation mid-point times for NEOWISE W1 and W2 detections are slightly earlier than the times given by the mjd value (see I.2.c.iii.1). For source detections made on images acquired before June 23, 2015 11:29:30.47 UTC (mjd=57196.47882488), the observation times are approximately 1.57±0.25sec earlier than the mjd values. For source detections after that date, the observation times are approximately 0.57±0.25 sec earlier than the mjd value.

 
scan_id%6s----no Identifier of the NEOWISE survey scan in which the predicted position of this SSO was observed.

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 boresight 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 related to the NEOWISE 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. Up through scan number 99799, SSSSS is twice the orbit number. Following scan number 99799, SSSSS rolls over to 01000, and is twice the orbit number, minus 98800. Scan numbers following the rollover are also distinguished by having different values of x.

  • x   is a letter assigned based on a sequential count of scans started in a specific half-orbit. For scans up to and including 99799, x="a" unless there is a second scan in the same half-orbit, in which case x="b". For scans after 99799, x="r" unless there is a second scan in the same half-orbit, in which case x="s".

The first scan whose data are used in the NEOWISE Data Release is scan 44212a. This was the first scan after the NEP crossing in the 22,106th WISE/NEOWISE orbit. The final scan included in the Release is 57041r, the first scan after the SEP crossing in the 77,920th orbit.

 
frame_num%3d----no Number of the Single-exposure frameset within which lies the predicted position of the SSO during the NEOWISE observation.

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:

fr_num = int[((frame_utc - dt_beg) - scan_start_utc)/bin_size] + 1

where

  • int[] means truncate to an integer
  • frame_utc is the nominal frame exposure center UTC (when the boresight 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.
 
source_id%16s----yesIdentifier of the NEOWISE Single-exposure Database detection that is spatially associated with the SSO predicted position at the time of the NEOWISE observation.

CAUTION: A spatial association between the predicted SSO position and the position of a NEOWISE Single-exposure extraction does not necessarily mean that this is a NEOWISE 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 NEOWISE extraction may be a chance alignment with a spurious extraction or an inertial background astrophysical source. See II.3.c for suggestions on how to identify reliable SSO detections.

This column is "null" if there is not a NEOWISE 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.
 
mconf%6.2f----yesSpatial association match confidence: 2-D chi-square parameter, max 99.99. This column is null if there is no associated NEOWISE extraction.  
n%4d----yesNumber of NEOWISE Single-exposure extractions within association threshold (max 9), 0 if no association  
m%4d----yesNumber of SSOs to which the associated NEOWISE detection is positionally matched (max 9), 0 if there the SSO does not have a NEOWISE detection association.  
dra%6.1farcsecyesRA distance between associated NEOWISE detection and predicted SSO position (NEOWISE - SSO).  
ddec%6.1farcsecyesDeclination distance between associated NEOWISE extraction and predicted SSO position (NEOWISE - SSO).  
w1mpro%7.3fmagyesSingle-exposure W1 profile-fit magnitude or magnitude upper limit for the NEOWISE detection spatially associated with the SSO. The column is null if there is no associated NEOWISE detection.  
w1sgmp%5.3fmagyesSingle-exposure W1 profile-fit photometric measurement uncertainty for the associated NEOWISE detection. This column is null if there is no associated NEOWISE extraction, or the W1 profile-fit magnitude of an associated detection is a 95% confidence upper limit.  
w2mpro%7.3fmagyesSingle-exposure W2 profile-fit magnitude or magnitude upper limit for the NEOWISE detection spatially associated with the SSO. The column is null if there is no associated NEOWISE detection.  
w2sgmp%5.3fmagyesSingle-exposure W1 profile-fit photometric measurement uncertainty for the associated NEOWISE detection. This column is null if there is no associated NEOWISE detection, or the W2 profile-fit magnitude of an associated detection is a 95% confidence upper limit.  
x%19.16f----yesUnit sphere (x,y,z) position x value  
y%19.16f----yesUnit sphere (x,y,z) position y value  
z%19.16f----yesUnit sphere (x,y,z) position z value  
spt_ind%9d----yesHTM spatial (x,y,z) index key  
htm20 %19ld ---- no Level 20 HTM spatial index key  


Last Updated: 9 February 2024


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