V. AllWISE Data Processing

V.2. Single-exposure Modifications In Preparation For AllWISE

V.2.b. Multiframe Position Reconstruction (MFPRex)—Updating band-frame positions

Table of Refined Single-exposure WCS Information

As described in V.2.b.i, the nominal Single-exposure image band-frame positions reconstructed during the original Scan/Frame processing were refined in preparation for AllWISE Multiframe processing. These refinements were derived by Multiframe Position Reconstruction (MFPRex) processing using proper motions from UCAC4 to adjust 2MASS Reference star positions while taking into account simultaneously the much larger set of source frame-to-frame position differences in image overlap regions. Because only stars with good quality UCAC4 proper motions are used, the number of reference stars is greatly reduced. However, the use of the large number of stars in the frame-to-frame overlaps compensates by indirectly transmitting reference star inputs from nearby frames.

This table contains the refined center positions, position angles and x and y pixel scales for each Single-exposure band frame. Note that WCS parameters in the Single-exposure image headers were not replaced with these refined values. The AllWISE Multiframe pipeline retrieved and utilized the MFPRex position refinements in the image coaddition and source extraction procedure.

The following table contains a description of the format and content of the Refined Single-exposure WCS Information table. The columns in the description table are:

Column Name: The parameter name in the Database table.

Format: The ASCII-equivalent format of the field in the Database, expressed in "C"-readable notation. This is useful when parsing the aligned tabular output from the IRSA General Catalog Search Engine. Although the data values will conform to these formats, the actual width of the field in the IRSA output may be padded with extra blank spaces to accommodate column headers. Note that some fields contain null values that will require special handling when parsing Database tables from IRSA General Catalog Search Engine output.

Units: The units of the parameter. A value of "----" in this column means that the parameter is dimensionless or non-numeric.

nulls: A "yes" in this column means that this parameter can be null in the Database. A "no" means that there will always be a value in this column in the Database.

Description: A brief description of the parameter and its values.

Column Name	Format	Units	nulls	Description
frmID	%9s	----	no	Frameset identifier. This is a nine character string that identifies the survey scan and individual frameset of this Single-exposure. The frame_id has the general form SSSSSxMMM, 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". MMM is a zero-filled three-digit number that gives the individual frameset in the scan. 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 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. The first frameset whose data are used in the AllWISE Multiframe Processing is frame 001 from scan 00712a, the first scan after the NEP crossing in the 356th WISE orbit. The final frameset included in the Database is frame 216 from scan 12514a, the first scan after the NEP crossing in the 6257th WISE orbit.
w1MFra	%10.6f	deg	no	Revised right ascension (J2000) of the W1 frame center.
w1MFdec	%10.6f	deg	no	Revised declination (J2000) of the W1 frame center.
w1MFpa	%10.6	deg	no	Revised image twist of the W1 frame: the position of the image y-axis West of North at the EQUINOX; in the opposite direction of the conventional Position Angle, where position angle (P.A.) = -CROTA0.
w1MFsfx	%14.11f	deg/pix	no	Revised X pixel scale factor of the W1 frame at the reference position of the image (crpix1,crpix2).
w1MFsfy	%14.11f	deg/pix	no	Revised Y pixel scale factor of the W1 frame at the reference position of the image (crpix1,crpix2).
w2MFra	%10.6f	deg	no	Revised right ascension (J2000) of the W2 frame center.
w2MFdec	%10.6f	deg	no	Revised declination (J2000) of the W2 frame center.
w2MFpa	%10.6	deg	no	Revised image twist of the W2 frame: the position of the image y-axis West of North at the EQUINOX; in the opposite direction of the conventional Position Angle, where position angle (P.A.) = -CROTA0.
w2MFsfx	%14.11f	deg/pix	no	Revised X pixel scale factor of the W2 frame at the reference position of the image (crpix1,crpix2).
w2MFsfy	%14.11f	deg/pix	no	Revised Y pixel scale factor of the W2 frame at the reference position of the image (crpix1,crpix2).
w3MFra	%10.6f	deg	yes	Revised right ascension (J2000) of the W3 frame center. A null value in this column indicates that this frameset did not have W3 data.
w3MFdec	%10.6f	deg	yes	Revised declination (J2000) of the W3 frame center. A null value in this column indicates that this frameset did not have W3 data.
w3MFpa	%10.6	deg	yes	Revised image twist of the W3 frame: the position of the image y-axis West of North at the EQUINOX; in the opposite direction of the conventional Position Angle, where position angle (P.A.) = -CROTA0. A null value in this column indicates that this frameset did not have W3 data.
w3MFsfx	%14.11f	deg/pix	yes	Revised X pixel scale factor of the W3 frame at the reference position of the image (crpix1,crpix2). A null value in this column indicates that this frameset did not have W3 data.
w3MFsfy	%14.11f	deg/pix	yes	Revised Y pixel scale factor of the W3 frame at the reference position of the image (crpix1,crpix2). A null value in this column indicates that this frameset did not have W3 data.
w4MFra	%10.6f	deg	yes	Revised right ascension (J2000) of the W4 frame center. A null value in this column indicates that this frameset did not have W4 data.
w4MFdec	%10.6f	deg	yes	Revised declination (J2000) of the W4 frame center. A null value in this column indicates that this frameset did not have W4 data.
w4MFpa	%10.6	deg	yes	Revised image twist of the W4 frame: the position of the image y-axis West of North at the EQUINOX; in the opposite direction of the conventional Position Angle, where position angle (P.A.) = -CROTA0. A null value in this column indicates that this frameset did not have W4 data.
w4MFsfx	%14.11f	deg/pix	yes	Revised X pixel scale factor of the W4 frame at the reference position of the image (crpix1,crpix2). A null value in this column indicates that this frameset did not have W4 data.
w4MFsfy	%14.11f	deg/pix	yes	Revised Y pixel scale factor of the W4 frame at the reference position of the image (crpix1,crpix2). A null value in this column indicates that this frameset did not have W4 data.
BID	%8s	----	no	MFPrex Bundle ID. An eight character strong that identifies the group or "bundle" of contiguous images, containing this particular Single-exposure image. For computational efficiency, MFPRex operated on 12,288 roughly equally spaced bundles of images. Each bundle covers approximately 3.36 deg².
cntr	%12d	----	no	Unique sequential identification number for the revised position table entry.

Last Update: 2017 February 17