Dark tiles 4014 and 11707 observed close to Moon on 20241020

[araichoor]

on 20241020, two dark tiles were observed clos-ish to the Moon:

• tileid=4014: expids=258979-258982, Moon distance: 56.7 deg;
• tileid=11707: expids=258984-258986, Moon distance: 49.2 deg.

they got 3-4 exposures, which all were >0.4 survey speed, and overall high efftime_spec. but their lrg success rate is lower than nominal.

here s the per-petal lrg success rate nightqa plot:

here s the sky map, with the grey shaded area showing 50 deg from the Moon:

and here are some stats for the five dark tiles observed that night, where one can see that tileids=4014 and 11707 are the dubious ones:

# TILEID NEXP EFFTIME_SPEC NGOOD_LRG/NLRG=GOOD_FRAC
8084    1    1103  637/649=0.98
6226    3    1295  330/339=0.97
5841    3    1421  309/315=0.98
4014    4    1506  635/665=0.95 # <- in des region, at dec~-17
11707   3    1314  823/905=0.91 # <- north of the ngc region

I guess we d want to mark those exposures as "bad" and reprocess?

for reference, slack threads:

• about the nts picking dark tiles issue: https://desisurvey.slack.com/archives/C01HNN87Y7J/p1729515239789439
• about those two dark tiles: https://desisurvey.slack.com/archives/C01HNN87Y7J/p1729534777365939

[sybenzvi]

I agree that 4104 and 11707 should be marked bad; these were mistaken observations and the redshift distribution looks off.