2MASS QA Scoring Rules RULES FOR QUALITY SCORING OF 2MASS SCANS
R. L. Hurt, J. D. Kirkpatrick (IPAC/Caltech), December 2000

These represent the current grading rules used for nightly QA evaluations.

Survey Scan Grading

Each scan is scored using a base quality number multiplied by the minimum of a series of quality factors as detailed below.

score = (base) * min(fct1, fct2, fct3, fct4, fct5)
fct1 ranges from 0.0 to 1.0; all others range from 0.1 to 1.0
score will always be >= 1 unless the photometric quality factor fct1 = 0
an additional fct7 is carried along with the score to flag untracked seeing but does not affect scoring (see below)

The "new" strategy of calibration is for observing a single calibration block at 1 hour intervals.

Base quality

For optimally dithered scans (after 970606n), base = 10.
For scans not optimally dithered (on or before 970606n), base = 5.

fct1/Photometric quality

A photometric quality factor applies to each photometric interval during a night. It roughly corresponds to a probability in meeting Level 1 specs.

A photometric interval is defined as 2 or more cal sets spanning photometric survey sets. The standard photometric grading strategy follows the form:

fct1 = (mult1) * (mult2) * (mult4)
fct1 is always rounded up to 0.1 unless the scan is non-photometric.
mult3 is a separate factor no longer implemented in QA but appears in archival rules.
A survey block is considered to be non-photometric under any of the following conditions:

It is not bounded on either side by calibration blocks passing CALMON with a photometric solution.
Scatter in overlaps summary exceeds 0.1 mag in any band (mult4).
Reasonable evidence for clouds is found in any of the scans in the block.

mult1/Number of Cal Blocks

Downgraded if number of cal sets in block < 5.

# of cal sets	mult1
4	0.9
3	0.8
2*	0.3 (0.8**)

* A solitary 2-cal interval is allowed to pass only if it is photometrically perfect in its cals' dispersions and overlaps and if its zero-point appears to be consistent.

**A factor of 0.8 applies for a 2-cal photometric interval that is spanned by a photometric solution spanning 3 or more cal sets; see below. Such a 2-cal subset of a longer interval is not subject to the stringent photometric requirements of a solitary 2-cal interval.

mult2/Photometric Dispersion

Downgraded if dispersion in photometry for field stars> 0.04 mag for one or more cal sets.
mult2 = 2 - ((worst dispersion)/0.04)
Downgrade used is the worst for any cal set in a given photometric interval.
Downgrade is waived if it occurs only for a high airmass (> ~1.5) cal set in an otherwise photometrically stable night. It may also be waived if it applies to only a single band of a single cal set which still has a zero point highly consistent with the other zero points that night.

mult4/Scatter in Overlaps

Downgraded if peak-peak spread of photometric repeatablility in overlaps region > 0.05 mag.
The worst observed overlaps downgrade within a single survey set applies to the entire survey set (sometimes a survey set may have two or more disjoint overlaps intervals or include unoverlapped scans).

Peak-Peak Scatter	mult4
< 0.05 mag	1.0
< 0.075 mag	0.7
< 0.1 mag	0.4
>= 0.1 mag	0.0

Downgrades for overlaps can be waived under the following conditions:

Overlaps are based on very few stars due to low source densities (poor statistics).
Dec overlap is limited to only a small portion of the scan (as with disjoint pole scans or N/S overlaps).
Overlap statistics are strongly biased by stars with poorly measured photometry (such as stars falling in bright star haloes or ones that are close doubles).
Peak-to-peak scatters that are a reflection only of the PSF cross-scan bias residual and not of the transmission of the atmosphere (as verified by lack of evidence of clouds in the background and/or magndec plots); this condition has been sometimes called "K-only clouds".

Clouds & Photometric Downgrades

If any evidence for clouds exist within a given survey set, then the photometric quality for that entire set will be set to fct1 = 0.0. Conditions indicating clouds include:

Large jumps in the overlaps summary plot
Swings in the magndec plots of > 0.2 mag across a scan.
K-bright jumps in the background frame median plots (can be J-bright under a full moon).
High numbers of K jump counter counts

Scans with no overlaps information that show suspicious background frame median plots should be considered to be non-photometric (guilty until proven innocent).

Note that under special circumstances a cloud event may be determined to be localized to a single scan, and only that scan is deemed non-photometric. Such an event is sometimes called a "con trail" and characteristically shows up on an otherwise perfectly clear night with no hint of clouds in either the observer's log or weather imagery. The cloud signature is very brief in the scan, suggestive of a very isolated event.

Clouds & Contiguous Photometric Intervals

Sometimes a valid photometric solution will span one or more non-photometric survey sets . In this case the photometric solution spanning this survey block should be allowed to stand as long as it appears to be a stable across the non-photometric period.

The survey scans to either side of this break will be graded as if that were an actual photometric break, with mult1 calculated from the number of cal sets that span the photometric interval (however a 2-cal interval will be downgraded only to 0.8, not 0.3). Any mult2 photmetric dispersion downgrades will apply to all intervals covered by the photometric solution, however, since it reflects uncertainty in the overall zero-point solution.

If the zero-point solution is not consistent across the interval, CALMON will be rerun after "breaking" the interval into photometric sub intervals by altering the .lgo file and setting the appropriate overrides.

fct2/Sensitivity

A sensitivity quality factor is computed from a convolution of the seeing shape and background level (PSP or point-source probability), and corresponds roughly to the probability that a scan will meet the Level 1 specs for sensitivity. The grades are dependent upon hemisphere and date (reflecting differing sensitivities of detectors).

Probability	North K PSP (& H before 990701)	North H PSP (after 990701)	South H PSP	South K PSP	fct2
>75%	<= 10.85	<= 9.0	<= 9.6	<= 10.6	1.0
50-75%	<= 11.11	<= 9.3	<= 9.8	<= 10.9	0.8
25-50%	<= 11.35	<= 9.5	<= 10.3	<= 11.7	0.5
0-25%	<= 11.85	<= 9.7	<= 11.7	<= 11.7	0.3
0%	> 11.85	> 9.7*	> 11.7	> 11.7	0.1

*Note that current Northern H PSP downgrades are only allowed to go down to 0.3, not 0.1, so this last condition does not apply.

fct3/Seeing Shape

Scans with poor seeing shapes are downgraded to fct3 = 0.1. Any of the following conditions warrants a downgrade:

Max J seeing shape > 1.3
Average J seeing shape > 1.25

A downgrade override is also warranted if there is any indication that the seetracker score is in error and does not properly detect a known problem (i.e. many false extended sources seen across a coadd).

Note that in a related downgrade, a scan with a 2nd image moment < 0.81 receives a maximum final quality grade of 1.

fct4/Untracked Seeing

Scans with extensive runs of untracked seeing are downgraded to fct4 = 0.1. The following conditions warrants a downgrade:

Untracked seeing extent (any band) > 900"

All untracked seeing scans are inspected to verify the downgrade is warranted and not caused by a galaxy cluster.

fct5/Airglow

Scans with strong residual structure in the coadds induced by OH airglow variations are downgraded to fct5 = 0.1. The following condition warrants a downgrade:

H cnoise4 > 4.5 & log(max source density) < 4.2

All airglow scans are inspected to verify the downgrade is warranted . The cnoise4 statistic is the difference between the measured coadd background noise (after modelling large-scale gradients & structure) and the theoretical noise expected from the overall background level. Reviewers should note that this theoretical noise level varies with time and may need to be updated periodically by Tom Jarrett.

Other Downgrades

Individual scans should also be set to quality 0 for any of the following reasons:

Bugs crawling on the window
Bright airplane passing through field
Transient illumination problems that generate significant structure in coadds (e.g. strong Dome jumps)
Transient electronics glitches or power failures
Image blurring due to earthquakes
Scans that fail due to unrecoverable problems in the data (e.g. observing too close to moon)

Single-frame electronics glitches (so far seen only in north H band) should not receive grades higher than 4 (however, there is currently no quality factor associated with this downgrade, but such cases will also be flagged with Bla0 = 1 in the SIT file).

Grades of scans may also be overridden on recommendation by UMASS (e.g. to force a single scan with a high grade to match the low grades of the rest of the block).

fct7/Untracked Seeing Eyeball Estimate

This final QA factor is carried along with the database transaction and SIT files for the night as a record of untracked seeing problems that have caused false extended source detections, even if the incident is not bad enough to warrant a downgrade. Reviewers inspect every scan with marginally high seetracker scores to look for obvious signs of point sources misidentified as extended. If such an incident is noted in at least two stars then the fct7 score is set to 0.0 for the scan (otherwise it is 1.0). The default is for fct7 to be set equal to fct4.

Currently fct7 is not used for grading scans but may be a useful flag in selecting candidates for reobservation.

Calibration Scan Grading

Calibration scans receive grades of either 0 or 10. Conditions sufficient to fail a single calibration scan (grade 0) are:

the scan failed processing at any stage
scan is in a block that CALMON does not pass as photometric
there is any evidence for clouds during the cal block, even if it technically passes

Conversely, any cal block that technically passes as photometric, even if it bounds non-photometric survey data or is not part of a solution spanning multiple blocks, should receive a grade of 10 for inclusion in the calibration working database. This is a change from previous rules in which cal blocks that bounded non-photometric data were themselves considered to be non-photometric.

Default Grading and Overrides

Much of the grading is computed automatically by the SCANSCI subsystem. This includes generation of the template QAreview and tile/database transaction files. If a default grade needs to be overridden the reviewer should enter that override into the YYMMDDH.qagrade file (found in the datequal directory) and use the /home/hurt/bin/run_scansci script to update the grading.

When overrides have been implemented they will show up on the second set of quality factors found on the "Scan Grading" section of the QA Report web pages.

Post-Processing Downgrades

A number of scans have been observed that do not overlap any adjacent tiles on the same night. To find potential photometric problems that would otherwise have been noticible in these overlaps, comparisons have been run between them and tiles from other nights to look for any photometric biases or evidence for clouds.

Scans in which clouds have been found are given retroactive downgrades to quality = 3, and they are also flagged with Bla1 = 1 in the SIT file.

Other scans have been found in which a clear, constant photometric bias is seen with respect to tiles on other nights. This indicates an incorrect zero-point determination, likely the result of weather-induced problems in these or nearby cal scans. If the bias is deemed sufficiently large to be a problem (~> 0.15 mag), the affected scans are flagged with Bla2 = 1 in the SIT file and their final quality scores are downgraded to 5 if they were higher than 5.

Last Updated 10/01/01 by R. Hurt