Debug (rare) invalid airmass values

[dkirkby]

@akremin has compared airmass values from the ETC json and DESI raw data header and found some (rare) examples of large discrepancies. The worst case is:

Night: 20210513, exp: 00088274, airmass etc: 1.54272, airmass data:1.104157, difference:-0.43856

Can you post your plot comparing all exposures here @akremin?

This matters for the ETC since airmass is used for its EFFTIME calculation.

[dkirkby]

The ETC uses the header dictionary provided by ICS with the GFA acquisition exposure. This does not contain AIRMASS, so I calculate it from the provided MOUNTEL as:

X = desietc.util.cos_zenith_to_airmass(np.sin(np.deg2rad(hdr['MOUNTEL'])))

Digging into 20210513/00088274:

cd $DESI_SPECTRO_DATA/20210513/00088274
fitsheader -e 1 -k AIRMASS desi-00088274.fits.fz
fitsheader -e 1 -k MOUNTEL guide-00088274-0000.fits.fz

This gives X=1.10 from the DESI header and X=1.01 calculated from MOUNTEL=65.3 deg from the acq image header (guide-00088274-0000.fits.fz), which is about the level of agreement we should expect.

However, the ETC got MOUNTEL=40.4 deg via ICS (stored as etc['expinfo']['elevation'] in the ETC json).

Any idea how these elevation angles could be so different (by 25 deg) @daqiii ?

[daqiii]

David, AIRMASS comes from the telescope and so does mountel there is no obvious explanation except that you are getting/ using stale data. could you check the telemetry db and see what the mount el was for the previous exposure? Get Outlook for iOS<https://aka.ms/o0ukef>

…

________________________________ From: David Kirkby ***@***.***> Sent: Thursday, September 9, 2021 9:11:00 PM To: desihub/desietc ***@***.***> Cc: Honscheid, Klaus ***@***.***>; Mention ***@***.***> Subject: Re: [desihub/desietc] Debug (rare) invalid airmass values (#3) The ETC uses the header dictionary provided by ICS with the GFA acquisition exposure. This does not contain AIRMASS, so I calculate it from the provided MOUNTEL as: X = desietc.util.cos_zenith_to_airmass(np.sin(np.deg2rad(hdr['MOUNTEL']))) Digging into 20210513/00088274: cd $DESI_SPECTRO_DATA/20210513/00088274 fitsheader -e 1 -k AIRMASS desi-00088274.fits.fz fitsheader -e 1 -k MOUNTEL guide-00088274-0000.fits.fz This gives X=1.10 from the DESI header and X=1.01 calculated from MOUNTEL=65.3 deg from the acq image header (guide-00088274-0000.fits.fz), which is about the level of agreement we should expect. However, the ETC got MOUNTEL=40.4 deg via ICS (stored as etc['expinfo']['elevation'] in the ETC json). Any idea how these elevation angles could be so different (by 25 deg) @daqiii<https://urldefense.com/v3/__https://github.com/daqiii__;!!KGKeukY!lsp4geCsufHsh-HJONZtft4ukPZva5KBubizF0mnE5diMtKkY4Cdc6eJNigl1nCVgQ$> ? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<https://urldefense.com/v3/__https://github.com/desihub/desietc/issues/3*issuecomment-916554687__;Iw!!KGKeukY!lsp4geCsufHsh-HJONZtft4ukPZva5KBubizF0mnE5diMtKkY4Cdc6eJNigkd3u_Kw$>, or unsubscribe<https://urldefense.com/v3/__https://github.com/notifications/unsubscribe-auth/ABQ5P62DTKEK62TIYX7G6GTUBFLKJANCNFSM5DYJJ7MQ__;!!KGKeukY!lsp4geCsufHsh-HJONZtft4ukPZva5KBubizF0mnE5diMtKkY4Cdc6eJNihg28ekcg$>. Triage notifications on the go with GitHub Mobile for iOS<https://urldefense.com/v3/__https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675__;!!KGKeukY!lsp4geCsufHsh-HJONZtft4ukPZva5KBubizF0mnE5diMtKkY4Cdc6eJNihiETcfdw$> or Android<https://urldefense.com/v3/__https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign*3Dnotification-email*26utm_medium*3Demail*26utm_source*3Dgithub__;JSUlJSU!!KGKeukY!lsp4geCsufHsh-HJONZtft4ukPZva5KBubizF0mnE5diMtKkY4Cdc6eJNij5zw6YOQ$>.