These represent the current grading rules used for nightly QA evaluations. Older grading rules are archived elsewhere.

Survey Scan Grading

• 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)

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 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

*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

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

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

• Untracked seeing extent (any band) > 900"

fct5/Airglow

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

Other Downgrades

• 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)

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

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

Calibration Scan Grading

• 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

Default Grading and Overrides

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

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.