III. NEOWISE Single-exposure Images

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 the 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 the 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 NEOWISE scan is 64272r, the first scan after the NEP crossing in the 81,536th orbit.

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 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 001 for a scan.

N.B. - The true observation mid-point times for NEOWISE images are slightly earlier than time reported in this column (see I.2.c.iii.1). For 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 report time. For images acquired after that date, the observation times are approximately 0.57±0.25 sec earlier than the reported value.

N.B. - The true observation mid-point times for NEOWISE images are slightly earlier than time reported in this column (see I.2.c.iii.1). For 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 report time. For images acquired after that date, the observation times are approximately 0.57±0.25 sec earlier than the reported value.

N.B. - The true observation mid-point times for NEOWISE images are slightly earlier than time reported in this column (see I.2.c.iii.1). For 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 report time. For images acquired after that date, the observation times are approximately 0.57±0.25 sec earlier than the reported value.

N.B. - The true observation mid-point times for NEOWISE images are slightly earlier than time reported in this column (see I.2.c.iii.1). For 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 report time. For images acquired after that date, the observation times are approximately 0.57±0.25 sec earlier than the reported value.

CAUTION: Single-exposure source database entries having negative or small positive (< 5.0) values of saa_sep should be used with caution. The large flux of charged particles within the SAA produces a very high incidence of radiation hits that can lead to contamination of real source measurements and to many spurious Single-exposure source extractions. Looking at the Single-exposure images taken of the same position when NEOWISE was not within the SAA is a good way to assess source reliability.

CAUTION: Single-exposure source database entries having qual_frame=0 should be used with extreme caution. They may be spurious detections of noise, transient events or scattered light, or if real, their position and/or flux measurements may be contaminated.

• SSSSSss = Scan identifier scan_id, with the letter in the last position translated into two zero-filled digits corresponding to the letter's place in the alphabet.


• MMM = Frame number frame_num, which is three zero-filled digits.


• IIIIII = six-digit, zero-filled, sequential extracted source number, src, within the frameset.

For example, a source in scan 44212a, frame number 057, with a source_id of 44212a057-000100, would have a cntr value of 4441201057000100.