================================= offline_matched_coadd_ccds_SURVEY ================================= :Summary: The ``gfa_reduce`` pipeline performs an "offline" analysis of full-frame DESI Guide-Focus-Alignment (GFA) images which does not influence observing operations in real time but nevertheless may provide useful metrics related to observing conditions and GFA detector behavior. For instance, ``gfa_reduce`` provides independent measurements of observing conditions such as seeing and transparency. :Naming Convention: ``offline_matched_coadd_ccds_{SURVEY}-thru_{NIGHT}.fits``, where ``{SURVEY}`` is *e.g.,* 'main' and ``{NIGHT}`` is the observation night in YYYYMMDD format. :Regex: ``offline_matched_coadd_ccds_(main|SV1|SV2|SV3)-thru_[0-9]{8}\.fits`` :File Type: FITS, 250 MB Contents ======== ====== ======================= ======== =============================================================================================== Number EXTNAME Type Contents ====== ======================= ======== =============================================================================================== HDU0_ IMAGE Empty HDU HDU1_ CAMERA_SUMMARY BINTABLE Summary results of individual guide cameras. HDU2_ EXPOSURE_SUMMARY BINTABLE Summary results accumulated per-exposure for all guide cameras. HDU3_ EXPOSURE_SUMMARY_STRICT BINTABLE Summary results accumulated per-exposure for all guide cameras with stricter data quality cuts. ====== ======================= ======== =============================================================================================== FITS Header Units ================= HDU0 ---- This HDU has no non-standard required keywords. Empty HDU. HDU1 ---- EXTNAME = CAMERA_SUMMARY ``CAMERA_SUMMARY`` is a simple concatenation of all per-exposure ``gfa_reduce`` ``_ccds`` tables. ``CAMERA_SUMMARY`` has one row per exposure per guider camera, so the total number of rows is roughly 6 times the number of exposures. There are more than 100 columns in the ``CAMERA_SUMMARY`` table, most of which shouldn't be relevant for the purpose of estimating effective exposure times. Required Header Keywords ~~~~~~~~~~~~~~~~~~~~~~~~ .. collapse:: Required Header Keywords Table .. rst-class:: keywords ====== ============= ==== ===================== KEY Example Value Type Comment ====== ============= ==== ===================== NAXIS1 1749 int length of dimension 1 NAXIS2 140700 int length of dimension 2 ====== ============= ==== ===================== Required Data Table Columns ~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. rst-class:: columns ============================ =========== ============= ================================================================================ Name Type Units Description ============================ =========== ============= ================================================================================ MEDIAN float64 adu Median of raw CCD image. MEAN float64 adu Mean of raw CCD image. N_NON_FINITE int64 adu Number of non-finite pixel values in raw CCD image. MAX float64 adu Max pixel value of raw CCD image. MIN float64 adu Min pixel value of raw CCD image. SIG_ROBUST float64 adu Robust standard deviation of raw CCD image. SIG float64 adu Standard deviation of raw CCD image. MEDIAN_Q1 float64 adu Median of quadrant 1 (amp G) MEAN_Q1 float64 adu Mean of quadrant 1 (amp G) N_NON_FINITE_Q1 int64 adu Number of non-finite pixel values in quadrant 1 (amp G) MAX_Q1 float64 adu Maximum raw GFA image pixel value in ADU in quadrant 1 (amp G) MIN_Q1 float64 adu Minimum raw GFA image pixel value in ADU in quadrant 1 (amp G) SIG_ROBUST_Q1 float64 adu Robust standard deviation of quadrant 1 (amp G) SIG_Q1 float64 adu Standard deviation of quadrant 1 (amp G) MEDIAN_Q2 float64 adu Median of quadrant 2 (amp H) MEAN_Q2 float64 adu Mean of quadrant 2 (amp H) N_NON_FINITE_Q2 int64 adu Number of non-finite pixel values in quadrant 2 (amp H) MAX_Q2 float64 adu Maximum raw GFA image pixel value in ADU in quadrant 2 (amp H) MIN_Q2 float64 adu Minimum raw GFA image pixel value in ADU in quadrant 2 (amp H) SIG_ROBUST_Q2 float64 adu Robust standard deviation of quadrant 2 (amp H) SIG_Q2 float64 adu Standard deviation of quadrant 2 (amp H) MEDIAN_Q3 float64 adu Median of quadrant 3 (amp E) MEAN_Q3 float64 adu Mean of quadrant 3 (amp E) N_NON_FINITE_Q3 int64 adu Number of non-finite pixel values in quadrant 3 (amp E) MAX_Q3 float64 adu Maximum raw GFA image pixel value in ADU in quadrant 3 (amp E) MIN_Q3 float64 adu Minimum raw GFA image pixel value in ADU in quadrant 3 (amp E) SIG_ROBUST_Q3 float64 adu Robust standard deviation of quadrant 3 (amp E) SIG_Q3 float64 adu Standard deviation of quadrant 3 (amp E) MEDIAN_Q4 float64 adu Median of quadrant 4 (amp F) MEAN_Q4 float64 adu Mean of quadrant 4 (amp F) N_NON_FINITE_Q4 int64 adu Number of non-finite pixel values in quadrant 4 (amp F) MAX_Q4 float64 adu Maximum raw GFA image pixel value in ADU in quadrant 4 (amp F) MIN_Q4 float64 adu Minimum raw GFA image pixel value in ADU in quadrant 4 (amp F) SIG_ROBUST_Q4 float64 adu Robust standard deviation of quadrant 4 (amp F) SIG_Q4 float64 adu Standard deviation of quadrant 4 (amp F) CAMERA char[6] Camera identifier. Passband and SPECGRPH ([brz][0-9]). EXTNAME char[6] String guide camera name; one of GUIDE0, GUIDE2, GUIDE3, GUIDE5, GUIDE7, GUIDE8 CONTRAST float64 Pattern-matching contrast for ``gfa_reduce`` astrometry; larger CONTRAST indicates a more robust astrometric solution SKY_MAG_AB float64 mag arcsec^-2 GFA-measured sky brightness. SKY_MAG_AB_SUBREGION float64 mag arcsec^-2 Sky brightness in a subregion of the GFA image. SKY_MAG_AB_PER_AMP float32[4] mag arcsec^-2 Per-amp GFA-measured sky brightness. PETAL_LOC binary Petal location [0-9] EXPID int64 DESI Exposure ID number MJD float64 d Modified Julian Date when shutter was opened for this exposure LST_DEG float64 deg Local Sidereal Time in degrees MOON_ILLUMINATION float64 Moon illumination fraction. PROGRAM char[88] DESI program type - BRIGHT, DARK, BACKUP, OTHER SKYRA float64 deg Boresight RA from TCS. SKYDEC float64 deg Boresight DEC from TCS. ZENITH_DIST_DEG float64 deg Boresight zenith distance. DOMSHUTL char[8] Dome lower shutter status inherited from TCS. DOMSHUTU char[8] Dome upper shutter status inherited from TCS. PMCOVER char[8] Primary mirror cover status inherited from TCS. MOONRA float64 deg RA of the Moon at the relevant epoch. MOONDEC float64 deg Dec of the Moon at the relevant epoch. MOON_ZD_DEG float64 deg Moon angular distance from zenith. T_C_FOR_DARK float64 deg Temperature used for dark current calculation (degrees Celsius). T_C_FOR_DARK_IS_GUESS int64 Flag for whether temperature for dark current was a guess due to lack of metadata. TIME_S_FOR_DARK float64 s Exposure time used for dark current calculation. NIGHT int64 Night of observation (YYYYMMDD) starting at local noon before observations start FOCUS char[39] Hexapod focus settings inherited from TCS. EXPTIME float64 s Length of time shutter was open CUBE_INDEX int64 Integer frame counter within the guide cube; ``CUBE_INDEX`` increases with time within each guide cube; 0 for acquisition images; -1 for matched coadds COADD_INDEX_START int64 Starting index of the coadd within the guider image cube sequence. COADD_INDEX_END int64 Ending index (inclusive) of the coadd within the guider image cube sequence. COADD_MJDOBS_MIN float64 d Minimum MJD of guider frames contributing to the coadd. COADD_MJDOBS_MAX float64 d Maximum MJD of guider frames contributing to the coadd. RACEN float64 deg Central RA of the guider image. DECCEN float64 deg Central Dec of the guider image. FNAME_RAW char[76] Raw file name for guider image cube. GITREV char[7] Git version for gfa_reduce software. FIBER_FRACFLUX float64 Fraction of flux in a DESI fiber for a point source. FIBER_FRACFLUX_ELG float64 Fraction of flux in a DESI fiber for a fiducial ELG morphology. FIBER_FRACFLUX_BGS float64 Fraction of flux in a DESI fiber for a fiducial BGS morphology. N_SOURCES_FOR_PSF int64 Number of sources used for PSF model ; key observing conditions quantities rely on the PSF model, so at least 3 sources for PSF-making is desirable APER_CORR_FAC float64 Correction factor to go from aperture to total light used for zeropoint determination. XCENTROID_PSF float64 pix Diagnostic giving PSF postage stamp's x-axis centroid location to potentially flag ill-determined PSF models. YCENTROID_PSF float64 pix Diagnostic giving PSF postage stamp's y-axis centroid location to potentially flag ill-determined PSF models. PSF_FWHM_PIX float64 pix PSF FWHM in pixels. PSF_FWHM_ASEC float64 arcsec PSF FWHM in arcseconds. PSF_CENTROID_CBOX float64 pix Centering box sidelength used for PSF centroid determination. PSF_CENTROID_FAILED int64 Flag indicating whether PSF centroiding failed. RADPROF_FWHM_ASEC float64 arcsec PSF FWHM in arcseconds determined from a fit to a 1-dimensional radial profile of the PSF. PSF_CENTROIDING_FLAG int64 Flag indicating potential issues with PSF centroiding. PSF_ASYMMETRY_RATIO float32 Dimensionless metric characterizing the level of PSF asymmetry. PSF_ASYMMETRY_NUMERATOR float32 Numerator of the PSF_ASYMMETRY_RATIO metric. PSF_ASYMMETRY_DENOMINATOR float32 Denominator of the PSF_ASYMMETRY_RATIO metric. PSF_TOTAL_FLUX float32 adu Total PSF flux. PROFILE_RADIUS_PIX float32[26] pix List of radius values in pixels for the PSF radial profile. PSF_RADIAL_PROFILE float32[26] List of PSF amplitude values for the PSF radial profile. MOUNTHA_HEADER float64 deg MOUNTHA hour angle inherited from TCS. MOUNTDEC_HEADER float64 deg MOUNTDEC declination inherited from TCS. HA_DEG float64 deg Boresight hour angle in degrees calculated independently of MOUNTHA reported by TCS. HA_DEG_PER_GFA float64 deg Hour angle in degrees for the relevant GFA camera. MOON_SEP_DEG float64 deg Boresight angular distance to the Moon. ZD_DEG_PER_GFA float64 deg Zenith distance in degrees calculated for the relevant GFA camera. HEADER_AIRMASS float64 AIRMASS inherited from TCS. AIRMASS float64 Boresight airmass calculated independently of TCS value. AIRMASS_PER_GFA float64 Airmass in degrees for the relevant GFA camera. ZP_ADU_PER_S float64 mag GFA camera zeropoint (r-band mag corresponding to total flux of 1 ADU/second). N_STARS_FOR_ZP int64 Number of stars used in computing the zeropoint. TRANSPARENCY float64 r-band transparency value for this GFA camera. KTERM float32 mag k-term in zeropoint calculation corresponding to this GFA camera's zenith distance. FRACFLUX_NOMINAL_POINTSOURCE float32 Point source fraction of flux for a circular aperture roughly approximating the size of a DESI fiber. FRACFLUX_NOMINAL_ELG float32 Fiducial ELG morphology fraction of flux for a circular aperture roughly approximating the size of a DESI fiber. FRACFLUX_NOMINAL_BGS float32 Fiducial BGS morphology fraction of flux for a circular aperture roughly approximating the size of a DESI fiber. DET_SN_THRESH float64 Detection signal-to-noise threshold used. NPIX_BAD_TOTAL int64 Number of bad pixels in overscan/prescan ; NPIX_BAD_TOTAL of 10 or larger may indicate insufficient GFA "denoising" (bad A/D conversion) NPIX_BAD_PER_AMP int64[4] Number of bad pixels for each amplifier in this GFA camera. OVERSCAN_MEDIANS_ADU float32[4] adu Overscan median pixel value per amp. PRESCAN_MEDIANS_ADU float32[4] adu Prescan median pixel value per amp. FWHM_MAJOR_PIX float64 pix FWHM along major axis of PSF. FWHM_MINOR_PIX float64 pix FWHM along minor axis of PSF. FWHM_PIX float64 pix PSF FWHM in pixels. FWHM_ASEC float64 arcsec PSF FWHM in arcseconds. N_SOURCES int64 Number of sources used for PSF determination. N_SOURCES_FOR_SHAPE int64 Number of sources whose shapes were individually measured. NAXIS int64[2] pix WCS solution parameter for GFA astrometry registered to Gaia. CD float64[4] WCS solution parameter for GFA astrometry registered to Gaia. CDELT float64[2] WCS solution parameter for GFA astrometry registered to Gaia. CRPIX float64[2] pix WCS solution parameter for GFA astrometry registered to Gaia. CRVAL float64[2] deg WCS solution parameter for GFA astrometry registered to Gaia. CTYPE char[16] WCS solution parameter for GFA astrometry registered to Gaia. LONGPOLE float64 deg WCS solution parameter for GFA astrometry registered to Gaia. LATPOLE float64 deg WCS solution parameter for GFA astrometry registered to Gaia. PV2 float64[2] WCS solution parameter for GFA astrometry registered to Gaia. FNAME_MASTER_DARK char[112] File name of master dark used for dark current correction. DO_FIT_DARK_SCALING binary Whether or not the master dark scaling was fit based on the GFA image itself. MASTER_DARK_EXPTIME float64 s Integration time of the dark exposures used to make the relevant master dark. MASTER_DARK_GCCDTEMP float64 deg Average CCD temperature of the dark exposures used to make the relevant master dark (Celsius). DARK_TEMP_SCALING_FACTOR float64 Factor by which the master dark was scaled based on CCD temperature. TOTAL_DARK_SCALING_FACTOR float64 Total factor by which the master dark was scaled accounting for both exposure time and CCD temperature. DARK_RESCALE_FACTORS_PER_AMP float64[4] Per-amp factor by which the master dark was scaled accounting for both exposure time and CCD temperature. DARK_RESCALE_FACTOR_BESTFIT float64 Master dark rescaling factor fit from the GFA image data itself. DARK_RESCALE_FACTOR_ADOPTED float64 Adopted master dark rescaling from either CCD temperature-based scaling or else from empirical fit to the GFA image iself. APPLY_DARK_RESCALE_FACTOR binary Whether or not the adopted dark rescaling factor was applied. DARK_RESCALE_NCALLS int64[4] Per-amp number of dark current rescaling fit iterations. DARK_RESCALE_CONVERGED binary[4] Per-amp indication of whether the dark current rescaling fit converged. REQ_MJD_MIN float64 d Input MJD lower bound for creating GFA image coadd. REQ_MJD_MAX float64 d Input MJD upper bound for creating GFA image coadd. N_PMGSTARS_ALL int64 Number of platemaker stars. N_PMGSTARS_RETAINED int64 Number of platemaker stars retained by platemaker. FIBERFAC float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming a point source profile. FIBERFAC_ELG float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming an ELG-like profile (r_half = 0.45 arcsec exponential) FIBERFAC_BGS float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming a BGS-like profile (r_half = 1.5 arcsec de Vaucouleurs) SPECTRO_EXPID int64 DESI spectroscopic exposure number. ============================ =========== ============= ================================================================================ HDU2 ---- EXTNAME = EXPOSURE_SUMMARY This HDU is intended to be the same as ``EXPOSURE_SUMMARY_STRICT``, except that ``EXPOSURE_SUMMARY`` employs more permissive quality cuts in the sense that no ``CONTRAST`` or ``N_SOURCES_FOR_PSF`` cuts are applied. ``EXPOSURE_SUMMARY`` still includes minimal quality cuts to remove cases of bad GFA readout such as broken A/D conversion (lack of denoising) and zero-valued quadrants. The idea behind ``EXPOSURE_SUMMARY`` is that it avoids cuts that could bias toward retaining cameras with relatively good observing conditions (*e.g.*, ``N_SOURCES_FOR_PSF`` is preferentially higher when the transparency is better and the sky brightness is lower). We found that in practice such biases generally don't matter at any appreciable level, so in general it's recommended to use ``EXPOSURE_SUMMARY_STRICT`` rather than ``EXPOSURE_SUMMARY``. The downside of ``EXPOSURE_SUMMARY`` is that in rare cases it may get very wrong values, especially for the transparency when ``gfa_reduce`` astrometric pattern matching has catastrophically failed (low CONTRAST parameter). In some cases the lack of a ``CONTRAST`` cut in ``EXPOSURE_SUMMARY`` can be valuable. In rare instances (such as very poor observing conditions) a science exposure can be omitted from ``EXPOSURE_SUMMARY_STRICT`` due to failed ``gfa_reduce`` astrometry. But the PMGSTARS forced photometry is still usable, since the PMGSTARS forced photometry proceeds as usual even if ``gfa_reduce`` astrometry has failed. For this reason, as of late April 2021, the spectroscopy pipeline's tSNR afterburner uses ``EXPOSURE_SUMMARY`` rather than ``EXPOSURE_SUMMARY_STRICT`` (PR `#1245`_). .. _`#1245`: ​https://github.com/desihub/desispec/pull/1245 .. _`DESI-5418`: https://desi.lbl.gov/DocDB/cgi-bin/private/ShowDocument?docid=5418 Required Header Keywords ~~~~~~~~~~~~~~~~~~~~~~~~ .. collapse:: Required Header Keywords Table .. rst-class:: keywords ====== ============= ==== ===================== KEY Example Value Type Comment ====== ============= ==== ===================== NAXIS1 364 int length of dimension 1 NAXIS2 23290 int length of dimension 2 ====== ============= ==== ===================== Required Data Table Columns ~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. rst-class:: columns ============================ ======== ============= ================================================================================ Name Type Units Description ============================ ======== ============= ================================================================================ EXPID int64 DESI Exposure ID number CUBE_INDEX int64 Integer frame counter within the guide cube; ``CUBE_INDEX`` increases with time within each guide cube; 0 for acquisition images; -1 for matched coadds NIGHT int64 Night of observation (YYYYMMDD) starting at local noon before observations start EXPTIME float64 s Exposure time; usually 5 seconds for guider frames, 15 seconds for acquisition images, and 5 seconds for matched coadds (average rather than sum) FNAME_RAW char[76] Raw file name processed by ``gfa_reduce`` SKYRA float64 deg Telescope bore sight RA taken from raw header metadata SKYDEC float64 deg Telescope bore sight Dec taken from raw header metadata PROGRAM char[88] DESI program type - BRIGHT, DARK, BACKUP, OTHER MOON_ILLUMINATION float64 Moon illumination fraction (0 to 1) MOON_ZD_DEG float64 deg Moon zenith distance in degrees MOON_SEP_DEG float64 deg Moon angular separation in degrees relative to the observation's sky location KTERM float32 Assumed r band k-term value in magnitudes per airmass; from `DESI-5418`_ FRACFLUX_NOMINAL_POINTSOURCE float32 Point source nominal fraction of light in 1.52 arcsec diameter fiber-like aperture FRACFLUX_NOMINAL_ELG float32 Nominal fraction of light in 1.52 arcsec diameter fiber-like aperture for an ELG-like profile (r_half = 0.45 arcsec exponential) FRACFLUX_NOMINAL_BGS float32 Nominal fraction of light in 1.52 arcsec diameter fiber-like aperture for a BGS-like profile (r_half = 1.5 arcsec de Vaucouleurs) MJD float64 d Modified Julian Date when shutter was opened for this exposure FWHM_ASEC float64 arcsec FWHM in arcseconds based on fitting the PSF with a beta = 3.5 Moffat profile TRANSPARENCY float64 Transparency in r band; based on comparison against PS1 r magnitudes; zeropoints from `DESI-5418`_; k-term given by ``KTERM`` column SKY_MAG_AB float64 mag arcsec^-2 r band sky brightness measured from detrended GFA background levels; AB mag per square arcsec; zeropoints from `DESI-5418`_ FIBER_FRACFLUX float64 Point source fraction of light in 1.52 arcsec diameter aperture ASSUMING THE APERTURE IS PERFECTLY ALIGNED WITH THE PSF CENTROID FIBER_FRACFLUX_ELG float64 Same as ``FIBER_FRACFLUX`` but for an ELG-like profile (r_half = 0.45 arcsec exponential) rather than a point source FIBER_FRACFLUX_BGS float64 Same as ``FIBER_FRACFLUX`` but for a BGS-like profile (r_half = 1.5 arcsec de Vaucouleurs) rather than a point source AIRMASS float64 Average airmass during this exposure RADPROF_FWHM_ASEC float64 arcsec PSF FWHM in arcsec measured directly from the PSF radial profile FIBERFAC float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming a point source profile FIBERFAC_ELG float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming an ELG-like profile (r_half = 0.45 arcsec exponential) FIBERFAC_BGS float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming a BGS-like profile (r_half = 1.5 arcsec de Vaucouleurs) MINCONTRAST float64 Minimum ``gfa_reduce`` astrometric pattern matching contrast parameter among retained cameras MAXCONTRAST float64 Maximum ``gfa_reduce`` astrometric pattern matching contrast parameter among retained cameras ============================ ======== ============= ================================================================================ HDU3 ---- EXTNAME = EXPOSURE_SUMMARY_STRICT This table aggregates information from ``CAMERA_SUMMARY`` on a per-exposure basis by taking the median across individual guide cameras, subject to some quality cuts applied to ``CAMERA_SUMMARY`` on a per-camera basis to remove potentially bad GFA measurements. These quality cuts are: * remove rows of ``CAMERA_SUMMARY`` with ``min(MAX_Q1, MAX_Q2, MAX_Q3, MAX_Q4) = 0``. Having a maximum raw pixel value of zero in a quadrant indicates a major readout problem. * remove rows of ``CAMERA_SUMMARY`` with ``NPIX_BAD_TOTAL >= 10``, since this is indicative of insufficient denoising (bad A/D conversion). * remove rows of ``CAMERA_SUMMARY`` with ``N_SOURCES_FOR_PSF < 3``. * remove rows of ``CAMERA_SUMMARY`` with ``CONTRAST < 2 (CONTRAST < 1.85)`` in the case of acquisition images (matched coadds). The goal is to remove instances where ``gfa_reduce`` astrometry pattern matching failed. Required Header Keywords ~~~~~~~~~~~~~~~~~~~~~~~~ .. collapse:: Required Header Keywords Table .. rst-class:: keywords ====== ============= ==== ===================== KEY Example Value Type Comment ====== ============= ==== ===================== NAXIS1 364 int length of dimension 1 NAXIS2 23142 int length of dimension 2 ====== ============= ==== ===================== Required Data Table Columns ~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. rst-class:: columns ============================ ======== ============= ================================================================================ Name Type Units Description ============================ ======== ============= ================================================================================ EXPID int64 DESI Exposure ID number CUBE_INDEX int64 Integer frame counter within the guide cube; ``CUBE_INDEX`` increases with time within each guide cube; 0 for acquisition images; -1 for matched coadds NIGHT int64 Night of observation (YYYYMMDD) starting at local noon before observations start EXPTIME float64 s Exposure time; usually 5 seconds for guider frames, 15 seconds for acquisition images, and 5 seconds for matched coadds (average rather than sum) FNAME_RAW char[76] Raw file name processed by ``gfa_reduce`` SKYRA float64 deg Telescope bore sight RA taken from raw header metadata SKYDEC float64 deg Telescope bore sight Dec taken from raw header metadata PROGRAM char[88] DESI program type - BRIGHT, DARK, BACKUP, OTHER MOON_ILLUMINATION float64 Moon illumination fraction (0 to 1) MOON_ZD_DEG float64 deg Moon zenith distance in degrees MOON_SEP_DEG float64 deg Moon angular separation in degrees relative to the observation's sky location KTERM float32 Assumed r band k-term value in magnitudes per airmass; from `DESI-5418`_ FRACFLUX_NOMINAL_POINTSOURCE float32 Point source nominal fraction of light in 1.52 arcsec diameter fiber-like aperture FRACFLUX_NOMINAL_ELG float32 Nominal fraction of light in 1.52 arcsec diameter fiber-like aperture for an ELG-like profile (r_half = 0.45 arcsec exponential) FRACFLUX_NOMINAL_BGS float32 Nominal fraction of light in 1.52 arcsec diameter fiber-like aperture for a BGS-like profile (r_half = 1.5 arcsec de Vaucouleurs) MJD float64 d Modified Julian Date when shutter was opened for this exposure FWHM_ASEC float64 arcsec FWHM in arcseconds based on fitting the PSF with a beta = 3.5 Moffat profile TRANSPARENCY float64 Transparency in r band; based on comparison against PS1 r magnitudes; zeropoints from `DESI-5418`_; k-term given by ``KTERM`` column SKY_MAG_AB float64 mag arcsec^-2 r band sky brightness measured from detrended GFA background levels; AB mag per square asec; zeropoints from `DESI-5418`_ FIBER_FRACFLUX float64 Point source fraction of light in 1.52 arcsec diameter aperture ASSUMING THE APERTURE IS PERFECTLY ALIGNED WITH THE PSF CENTROID FIBER_FRACFLUX_ELG float64 Same as ``FIBER_FRACFLUX`` but for an ELG-like profile (r_half = 0.45 arcsec exponential) rather than a point source FIBER_FRACFLUX_BGS float64 Same as ``FIBER_FRACFLUX`` but for a BGS-like profile (r_half = 1.5 arcsec de Vaucouleurs) rather than a point source AIRMASS float64 Average airmass during this exposure RADPROF_FWHM_ASEC float64 arcsec PSF FWHM in arcsec measured directly from the PSF radial profile FIBERFAC float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming a point source profile FIBERFAC_ELG float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming an ELG-like profile (r_half = 0.45 arcsec exponential) FIBERFAC_BGS float64 PMGSTARS forced photometry amount of light in 1.52 arcsec diameter aperture normalized to nominal, assuming a BGS-like profile (r_half = 1.5 arcsec de Vaucouleurs) MINCONTRAST float64 Minimum ``gfa_reduce`` astrometric pattern matching contrast parameter among retained cameras MAXCONTRAST float64 Maximum ``gfa_reduce`` astrometric pattern matching contrast parameter among retained cameras ============================ ======== ============= ================================================================================