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spectra-SURVEY-PROGRAM-PIXNUM.rst

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spectra-SURVEY-PROGRAM-PIXNUM.fits

Summary:DESI spectra grouped by nested healpix number
Naming Convention:spectra-SURVEY-PROGRAM-PIXNUM.fits, where SURVEY is e.g. main or sv1, PROGRAM is e.g. bright or dark and PIXNUM is the HEALPixel number.
Regex:spectra-(cmx|main|special|sv1|sv2|sv3)-(backup|bright|dark|other)-[0-9]+\.fits
File Type:FITS, 408 MB

Spectra files contain non-coadded spectra for multiple targets observed on multiple individual exposures and cameras. The format can contain any arbitrary set of targets, though the standard DESI spectroscopic pipeline outputs are grouped either by a single petal of a given tile, or all targets on a single healpix.

Tile-based spectra can be grouped in multiple ways across exposures and nights; see the top-level :doc:`SPECPROD/tiles/ <../../../index>` description for an overview of the per-tile GROUPTYPE and GROUPID options. Healpix-based spectra are grouped by SURVEY and PROGRAM. Science analyses may release spectra in other groups, e.g. all the spectra selected for a particular analysis.

Please see :doc:`coadd files <coadd-SURVEY-PROGRAM-PIXNUM>` for a coadded version of the same spectra in a very similar format.

The FIBERMAP table contains metadata about each target, with one row per target per exposure. The corresponding SCORES table contains quantities measured from the spectra, also with one row per target per exposure.

The spectra themselves are in a set of image HDUs for the FLUX, IVAR (inverse variance), MASK, and spectral RESOLUTION, each prefixed with a spectrograph camera name, e.g. B, R, or Z for DESI, though the format in general could support other numbers and names of cameras for other instruments. A row of each image HDU correponds to the target from the same row index of the FIBERMAP and SCORES HDUs.

See the end of :doc:`tile-based spectra </DESI_SPECTRO_REDUX/SPECPROD/tiles/GROUPTYPE/TILEID/GROUPID/spectra-SPECTROGRAPH-TILEID-GROUPID>` for examples of reading this file format.

Note: the table below is the order in which these HDUs appear in DESI spectroscopic pipeline output, but the order is arbitrary and they should be read by name not by number.

Contents

Number EXTNAME Type Contents
HDU00   IMAGE Empty
HDU01 FIBERMAP BINTABLE fibermap table
HDU02 SCORES BINTABLE scores table
HDU03 B_WAVELENGTH IMAGE Wavelength array of b-channel spectra
HDU04 B_FLUX IMAGE Flux of b-channel spectra
HDU05 B_IVAR IMAGE Inverse variance of b-channel spectra
HDU06 B_MASK BINTABLE Mask of b-channel spectra
HDU07 B_RESOLUTION IMAGE Resolution matrices of b-channel spectra
HDU08 R_WAVELENGTH IMAGE Wavelength array of r-channel spectra
HDU09 R_FLUX IMAGE Flux of r-channel spectra
HDU10 R_IVAR IMAGE Inverse variance of r-channel spectra
HDU11 R_MASK BINTABLE Mask of r-channel spectra
HDU12 R_RESOLUTION IMAGE Resolution matrices of r-channel spectra
HDU13 Z_WAVELENGTH IMAGE Wavelength array of z-channel spectra
HDU14 Z_FLUX IMAGE Flux of z-channel spectra
HDU15 Z_IVAR IMAGE Inverse variance of z-channel spectra
HDU16 Z_MASK BINTABLE Mask of z-channel spectra
HDU17 Z_RESOLUTION IMAGE Resolution matrices of z-channel spectra

FITS Header Units

HDU00

HEALPixel keywords.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ======== ================ ==== ==============================================
    KEY      Example Value    Type Comment
    ======== ================ ==== ==============================================
    SPGRP    healpix          str  Spectral grouping method
    SPGRPVAL 26371            int  Grouping value = healpixel number
    HPXPIXEL 26371            int  Nested nside=64 healpixel number
    HPXNSIDE 64               int  Healpix nside
    HPXNEST  True             str  Healpix nested? (vs. ring)
    SURVEY   main             str  DESI Survey (sv1, sv3, main...)
    PROGRAM  bright           str  DESI Program (dark, bright, ...)
    CHECKSUM 8DPU9BMR8BMR8BMR str  HDU checksum updated 2021-07-19T17:59:29
    DATASUM  0                str  data unit checksum updated 2021-07-19T17:59:29
    ======== ================ ==== ==============================================

Empty HDU.

HDU01

EXTNAME = FIBERMAP

Fibermap table with per-target metdata.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ======== ================ ==== ==============================================
    KEY      Example Value    Type Comment
    ======== ================ ==== ==============================================
    NAXIS1   413              int  Width of table in bytes
    NAXIS2   1031             int  Number of rows in table
    CHECKSUM U9Fia89iV8Cia89i str  HDU checksum
    DATASUM  3589169610       str  data unit checksum
    ======== ================ ==== ==============================================

Required Data Table Columns

Propagated from the FIBERMAP HDU of the input :doc:`cframe files </DESI_SPECTRO_REDUX/SPECPROD/exposures/NIGHT/EXPID/cframe-CAMERA-EXPID>`.

.. rst-class:: columns
Name Type Units Description
TARGETID int64   Unique DESI target ID
PETAL_LOC int16   Petal location [0-9]
DEVICE_LOC int32   Device location on focal plane [0-523]
LOCATION int64   Location on the focal plane PETAL_LOC*1000 + DEVICE_LOC
FIBER int32   Fiber ID on the CCDs [0-4999]
FIBERSTATUS int32   Fiber status mask. 0=good
TARGET_RA float64 deg Barycentric right ascension in ICRS
TARGET_DEC float64 deg Barycentric declination in ICRS
PMRA float32 mas yr^-1 proper motion in the +RA direction (already including cos(dec))
PMDEC float32 mas yr^-1 Proper motion in the +Dec direction
REF_EPOCH float32 yr Reference epoch for Gaia/Tycho astrometry. Typically 2015.5 for Gaia
LAMBDA_REF float32 Angstrom Requested wavelength at which targets should be centered on fibers
FA_TARGET int64   Targeting bit internally used by fiberassign (linked with FA_TYPE)
FA_TYPE binary   Fiberassign internal target type (science, standard, sky, safe, suppsky)
OBJTYPE char[3]   Object type: TGT, SKY, NON, BAD
FIBERASSIGN_X float32 mm Fiberassign expected CS5 X location on focal plane
FIBERASSIGN_Y float32 mm Fiberassign expected CS5 Y location on focal plane
PRIORITY int32   Target current priority
SUBPRIORITY float64   Random subpriority [0-1) to break assignment ties
OBSCONDITIONS int32   Bitmask of allowed observing conditions
RELEASE int16   Imaging surveys release ID
BRICKID int32   Brick ID from tractor input
BRICK_OBJID int32   Imaging Surveys OBJID on that brick
MORPHTYPE char[4]   Imaging Surveys morphological type from Tractor
FLUX_G float32 nanomaggy Flux in the Legacy Survey g-band (AB)
FLUX_R float32 nanomaggy Flux in the Legacy Survey r-band (AB)
FLUX_Z float32 nanomaggy Flux in the Legacy Survey z-band (AB)
FLUX_IVAR_G float32 nanomaggy^-2 Inverse variance of FLUX_G (AB)
FLUX_IVAR_R float32 nanomaggy^-2 Inverse variance of FLUX_R (AB)
FLUX_IVAR_Z float32 nanomaggy^-2 Inverse variance of FLUX_Z (AB)
MASKBITS int16   Bitwise mask from the imaging indicating potential issue or blending
REF_ID int64   Tyc1*1,000,000+Tyc2*10+Tyc3 for Tycho-2; “sourceid” for Gaia DR2
REF_CAT char[2]   Reference catalog source for star: “T2” for Tycho-2, “G2” for Gaia DR2, “L2” for the SGA, empty otherwise
GAIA_PHOT_G_MEAN_MAG float32 mag Gaia G band magnitude
GAIA_PHOT_BP_MEAN_MAG float32 mag Gaia BP band magnitude
GAIA_PHOT_RP_MEAN_MAG float32 mag Gaia RP band magnitude
PARALLAX float32 mas Reference catalog parallax
BRICKNAME char[8]   Brick name from tractor input
EBV float32 mag Galactic extinction E(B-V) reddening from SFD98
FLUX_W1 float32 nanomaggy WISE flux in W1 (AB)
FLUX_W2 float32 nanomaggy WISE flux in W2 (AB)
FLUX_IVAR_W1 float32 nanomaggy^-2 Inverse variance of FLUX_W1 (AB)
FLUX_IVAR_W2 float32 nanomaggy^-2 Inverse variance of FLUX_W2 (AB)
FIBERFLUX_G float32 nanomaggy Predicted g-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_R float32 nanomaggy Predicted r-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERFLUX_Z float32 nanomaggy Predicted z-band flux within a fiber of diameter 1.5 arcsec from this object in 1 arcsec Gaussian seeing
FIBERTOTFLUX_G float32 nanomaggy Predicted g-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
FIBERTOTFLUX_R float32 nanomaggy Predicted r-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
FIBERTOTFLUX_Z float32 nanomaggy Predicted z-band flux within a fiber of diameter 1.5 arcsec from all sources at this location in 1 arcsec Gaussian seeing
SERSIC float32   Power-law index for the Sersic profile model (MORPHTYPE=”SER”)
SHAPE_R float32 arcsec Half-light radius of galaxy model (&gt;0)
SHAPE_E1 float32   Ellipticity component 1 of galaxy model for galaxy type MORPHTYPE
SHAPE_E2 float32   Ellipticity component 2 of galaxy model for galaxy type MORPHTYPE
PHOTSYS char[1]   &#x27;N&#x27; for the MzLS/BASS photometric system, &#x27;S&#x27; for DECaLS
PRIORITY_INIT int64   Target initial priority from target selection bitmasks and OBSCONDITIONS
NUMOBS_INIT int64   Initial number of observations for target calculated across target selection bitmasks and OBSCONDITIONS
SV1_DESI_TARGET [1] int64   DESI (dark time program) target selection bitmask for SV1
SV1_BGS_TARGET [1] int64   BGS (bright time program) target selection bitmask for SV1
SV1_MWS_TARGET [1] int64   MWS (bright time program) target selection bitmask for SV1
SV1_SCND_TARGET [1] int64   Secondary target selection bitmask for SV1
DESI_TARGET int64   DESI (dark time program) target selection bitmask
BGS_TARGET int64   BGS (Bright Galaxy Survey) target selection bitmask
MWS_TARGET int64   Milky Way Survey targeting bits
SCND_TARGET int64   Target selection bitmask for secondary programs
PLATE_RA float64 deg Barycentric Right Ascension in ICRS to be used by PlateMaker
PLATE_DEC float64 deg Barycentric Declination in ICRS to be used by PlateMaker
NUM_ITER int64   Number of positioner iterations
FIBER_X float64 mm CS5 X location requested by PlateMaker
FIBER_Y float64 mm CS5 Y location requested by PlateMaker
DELTA_X float64 mm CS5 X requested minus actual position
DELTA_Y float64 mm CS5 Y requested minus actual position
FIBER_RA float64 deg RA of actual fiber position
FIBER_DEC float64 deg DEC of actual fiber position
EXPTIME float64 s Length of time shutter was open
PSF_TO_FIBER_SPECFLUX float64   fraction of light from point-like source captured by 1.5 arcsec diameter fiber given atmospheric seeing
NIGHT int32    
EXPID int32   DESI Exposure ID number
MJD float64   Modified Julian Date when shutter was opened for this exposure
TILEID int32   Unique DESI tile ID
[1](1, 2, 3, 4) Optional

HDU02

EXTNAME = SCORES

Scores / metrics measured from the spectra for use in QA and systematics studies. These are propagated from the input :doc:`cframe SCORES HDU </DESI_SPECTRO_REDUX/SPECPROD/exposures/NIGHT/EXPID/cframe-CAMERA-EXPID>`.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== =======================
    KEY    Example Value Type Comment
    ====== ============= ==== =======================
    NAXIS1 488           int  width of table in bytes
    NAXIS2 1031          int  number of rows in table
    ====== ============= ==== =======================

Required Data Table Columns

.. rst-class:: columns
Name Type Units Description
TARGETID int64   Unique DESI target ID
SUM_RAW_COUNT_B float64   Sum of raw counts in B camera
MEDIAN_RAW_COUNT_B float64   Median of raw counts in B camera
MEDIAN_RAW_SNR_B float64   Median(raw signal/noise) in B camera
SUM_FFLAT_COUNT_B float64   Sum of fiber-flatfielded counts B camera
MEDIAN_FFLAT_COUNT_B float64   Median of fiber-flatfielded counts in B camera
MEDIAN_FFLAT_SNR_B float64   Median(S/N) of fiberflatfielded counts in B camera
SUM_SKYSUB_COUNT_B float64   Sum of sky-subtracted counts in B camera
MEDIAN_SKYSUB_COUNT_B float64   Median of sky-subtracted counts in B camera
MEDIAN_SKYSUB_SNR_B float64   Median(S/N) of sky-subtracted counts in B camera
SUM_CALIB_COUNT_B float64   Sum of calibrated flux in B camera
MEDIAN_CALIB_COUNT_B float64   Median of calibrated flux in B camera
MEDIAN_CALIB_SNR_B float64   Median(S/N) of calibrated flux in B camera
TSNR2_GPBDARK_B float64   template (S/N)^2 for dark targets in guider pass band on B
TSNR2_ELG_B float64   ELG B template (S/N)^2
TSNR2_GPBBRIGHT_B float64   template (S/N)^2 for bright targets in guider pass band on B
TSNR2_LYA_B float64   LYA B template (S/N)^2
TSNR2_BGS_B float64   BGS B template (S/N)^2
TSNR2_GPBBACKUP_B float64    
TSNR2_QSO_B float64   QSO B template (S/N)^2
TSNR2_LRG_B float64   LRG B template (S/N)^2
SUM_RAW_COUNT_R float64   Sum of raw counts in R camera
MEDIAN_RAW_COUNT_R float64   Median of raw counts in R camera
MEDIAN_RAW_SNR_R float64   Median(raw signal/noise) in R camera
SUM_FFLAT_COUNT_R float64   Sum of fiber-flatfielded counts R camera
MEDIAN_FFLAT_COUNT_R float64   Median of fiber-flatfielded counts in R camera
MEDIAN_FFLAT_SNR_R float64   Median(S/N) of fiberflatfielded counts in R camera
SUM_SKYSUB_COUNT_R float64   Sum of sky-subtracted counts in R camera
MEDIAN_SKYSUB_COUNT_R float64   Median of sky-subtracted counts in R camera
MEDIAN_SKYSUB_SNR_R float64   Median(S/N) of sky-subtracted counts in R camera
SUM_CALIB_COUNT_R float64   Sum of calibrated flux in R camera
MEDIAN_CALIB_COUNT_R float64   Median of calibrated flux in R camera
MEDIAN_CALIB_SNR_R float64   Median(S/N) of calibrated flux in R camera
TSNR2_GPBDARK_R float64   template (S/N)^2 for dark targets in guider pass band on R
TSNR2_ELG_R float64   ELG R template (S/N)^2
TSNR2_GPBBRIGHT_R float64   template (S/N)^2 for bright targets in guider pass band on R
TSNR2_LYA_R float64   LYA R template (S/N)^2
TSNR2_BGS_R float64   BGS R template (S/N)^2
TSNR2_GPBBACKUP_R float64    
TSNR2_QSO_R float64   QSO R template (S/N)^2
TSNR2_LRG_R float64   LRG R template (S/N)^2
SUM_RAW_COUNT_Z float64   Sum of raw counts in Z camera
MEDIAN_RAW_COUNT_Z float64   Median of raw counts in Z camera
MEDIAN_RAW_SNR_Z float64   Median(raw signal/noise) in Z camera
SUM_FFLAT_COUNT_Z float64   Sum of fiber-flatfielded counts Z camera
MEDIAN_FFLAT_COUNT_Z float64   Median of fiber-flatfielded counts in Z camera
MEDIAN_FFLAT_SNR_Z float64   Median(S/N) of fiberflatfielded counts in Z camera
SUM_SKYSUB_COUNT_Z float64   Sum of sky-subtracted counts in Z camera
MEDIAN_SKYSUB_COUNT_Z float64   Median of sky-subtracted counts in Z camera
MEDIAN_SKYSUB_SNR_Z float64   Median(S/N) of sky-subtracted counts in Z camera
SUM_CALIB_COUNT_Z float64   Sum of calibrated flux in Z camera
MEDIAN_CALIB_COUNT_Z float64   Median of calibrated flux in Z camera
MEDIAN_CALIB_SNR_Z float64   Median(S/N) of calibrated flux in Z camera
TSNR2_GPBDARK_Z float64   template (S/N)^2 for dark targets in guider pass band on Z
TSNR2_ELG_Z float64   ELG Z template (S/N)^2
TSNR2_GPBBRIGHT_Z float64   template (S/N)^2 for bright targets in guider pass band on Z
TSNR2_LYA_Z float64   LYA Z template (S/N)^2
TSNR2_BGS_Z float64   BGS Z template (S/N)^2
TSNR2_GPBBACKUP_Z float64    
TSNR2_QSO_Z float64   QSO Z template (S/N)^2
TSNR2_LRG_Z float64   LRG Z template (S/N)^2

HDU03

EXTNAME = B_WAVELENGTH

1D array of B-camera wavelengths in Angstrom, in vacuum (not in air), in the rest frame of the solar system barycenter.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== =====================
    KEY    Example Value Type Comment
    ====== ============= ==== =====================
    NAXIS1 2751          int  Number of wavelengths
    BUNIT  Angstrom      str
    ====== ============= ==== =====================

Data: FITS image [float64, 2751]

HDU04

EXTNAME = B_FLUX

2D array of calibrated spectral flux of dimension [nspec, nwave] in units of 1e-17 erg / (s cm2 Angstrom). nspec is the number of fibers per camera. nwave in the length of the wavelength array. The spectra of all fibers share the same wavelength grid, given in HDU B_WAVELENGTH.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============================ ==== =====================
    KEY    Example Value                Type Comment
    ====== ============================ ==== =====================
    NAXIS1 2751                         int  ``nwave`` number of wavelengths
    NAXIS2 1031                         int  ``nspec`` number of spectra
    BUNIT  10**-17 erg/(s cm2 Angstrom) str
    ====== ============================ ==== =====================

Data: FITS image [float32, 2751x1031]

HDU05

EXTNAME = B_IVAR

Inverse variance of flux (1/sigma^2) in units of (10^{-17} erg/s/cm2/A)^-2. Uncertainties comprise statistical uncertainties from the error propagation of the initial CCD pixel variance, the calibration uncertainties, plus an additional term on bright sky lines to account for the imperfect sky subtraction.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ================================= ==== =====================
    KEY    Example Value                     Type Comment
    ====== ================================= ==== =====================
    NAXIS1 2751                              int  ``nwave`` number of wavelengths
    NAXIS2 1031                              int  ``nspec`` number of spectra
    BUNIT  10**+34 (s2 cm4 Angstrom2) / erg2 str
    ====== ================================= ==== =====================

Data: FITS image [float32, 2751x1031]

HDU06

EXTNAME = B_MASK

Mask of spectral data; 0=good. See the :doc:`bitmask documentation </bitmasks>` page for the definition of the bits.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== ==========================================
    KEY    Example Value Type Comment
    ====== ============= ==== ==========================================
    NAXIS1 2751          int  ``nwave`` number of wavelengths
    NAXIS2 1031          int  ``nspec`` number of spectra
    BZERO  2147483648    int  offset data range to that of unsigned long
    BSCALE 1             int  default scaling factor
    ====== ============= ==== ==========================================

Data: FITS image [int32 (compressed), 2751x1031]

HDU07

EXTNAME = B_RESOLUTION

Resolution matrix stored as a 3D sparse matrix, modeling the per-fiber non-Gaussian effective line-spread-function resolution. See the :doc:`frame RESOLUTION HDU </DESI_SPECTRO_REDUX/SPECPROD/exposures/NIGHT/EXPID/frame-CAMERA-EXPID>` documentation for details about using this HDU.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== =====================
    KEY    Example Value Type Comment
    ====== ============= ==== =====================
    NAXIS1 2751          int  ``nwave`` number of wavelengths
    NAXIS2 11            int  ``ndiag`` number of diagonals
    NAXIS3 1031          int  ``nspec`` number of spectra
    ====== ============= ==== =====================

Data: FITS image [float32, 2751x11x1031]

A sparse resolution matrix may be created for spectrum i with:

from desispec.resolution import Resolution
R = Resolution(data[i])

Or using lower-level scipy.sparse matrices:

import scipy.sparse
import numpy as np
nspec, ndiag, nwave = data.shape
offsets = ndiag//2 - np.arange(ndiag, dtype=int)
R = scipy.sparse.dia_matrix((data[i], offsets), shape=(nwave, nwave))

HDU08

EXTNAME = R_WAVELENGTH

1D array of R-camera wavelengths in Angstrom, in vacuum (not in air), in the rest frame of the solar system barycenter.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== =====================
    KEY    Example Value Type Comment
    ====== ============= ==== =====================
    NAXIS1 2326          int  number of wavelengths
    BUNIT  Angstrom      str
    ====== ============= ==== =====================

Data: FITS image [float64, 2326]

HDU09

EXTNAME = R_FLUX

2D array of calibrated spectral flux of dimension [nspec, nwave] in units of 1e-17 erg / (s cm2 Angstrom). nspec is the number of fibers per camera. nwave in the length of the wavelength array. The spectra of all fibers share the same wavelength grid, given in HDU R_WAVELENGTH.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============================ ==== =====================
    KEY    Example Value                Type Comment
    ====== ============================ ==== =====================
    NAXIS1 2326                         int  ``nwave`` number of wavelengths
    NAXIS2 1031                         int  ``nspec`` number of spectra
    BUNIT  10**-17 erg/(s cm2 Angstrom) str
    ====== ============================ ==== =====================

Data: FITS image [float32, 2326x1031]

HDU10

EXTNAME = R_IVAR

Inverse variance of flux (1/sigma^2) in units of (10^{-17} erg/s/cm2/A)^-2. Uncertainties comprise statistical uncertainties from the error propagation of the initial CCD pixel variance, the calibration uncertainties, plus an additional term on bright sky lines to account for the imperfect sky subtraction.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ================================= ==== =====================
    KEY    Example Value                     Type Comment
    ====== ================================= ==== =====================
    NAXIS1 2326                              int  ``nwave`` number of wavelengths
    NAXIS2 1031                              int  ``nspec`` number of spectra
    BUNIT  10**+34 (s2 cm4 Angstrom2) / erg2 str
    ====== ================================= ==== =====================

Data: FITS image [float32, 2326x1031]

HDU11

EXTNAME = R_MASK

Mask of spectral data; 0=good. See the :doc:`bitmask documentation </bitmasks>` page for the definition of the bits.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== ==========================================
    KEY    Example Value Type Comment
    ====== ============= ==== ==========================================
    NAXIS1 2326          int  ``nwave`` number of wavelengths
    NAXIS2 1031          int  ``nspec`` number of spectra
    BZERO  2147483648    int  offset data range to that of unsigned long
    BSCALE 1             int  default scaling factor
    ====== ============= ==== ==========================================

Data: FITS image [int32 (compressed), 2326x1031]

HDU12

EXTNAME = R_RESOLUTION

Resolution matrix stored as a 3D sparse matrix, modeling the per-fiber non-Gaussian effective line-spread-function resolution. See the :doc:`frame RESOLUTION HDU </DESI_SPECTRO_REDUX/SPECPROD/exposures/NIGHT/EXPID/frame-CAMERA-EXPID>` documentation for details about using this HDU.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== =====================
    KEY    Example Value Type Comment
    ====== ============= ==== =====================
    NAXIS1 2326          int  length of data axis 1
    NAXIS2 11            int  length of data axis 2
    NAXIS3 1031          int  length of data axis 3
    ====== ============= ==== =====================

Data: FITS image [float32, 2326x11x1031]

HDU13

EXTNAME = Z_WAVELENGTH

1D array of Z-camera wavelengths in Angstrom, in vacuum (not in air), in the rest frame of the solar system barycenter.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== =====================
    KEY    Example Value Type Comment
    ====== ============= ==== =====================
    NAXIS1 2881          int  ``nwave`` number of wavelengths
    BUNIT  Angstrom      str
    ====== ============= ==== =====================

Data: FITS image [float64, 2881]

HDU14

EXTNAME = Z_FLUX

2D array of calibrated spectral flux of dimension [nspec, nwave] in units of 1e-17 erg / (s cm2 Angstrom). nspec is the number of fibers per camera. nwave in the length of the wavelength array. The spectra of all fibers share the same wavelength grid, given in HDU Z_WAVELENGTH.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============================ ==== =====================
    KEY    Example Value                Type Comment
    ====== ============================ ==== =====================
    NAXIS1 2881                         int  ``nwave`` number of wavelengths
    NAXIS2 1031                         int  ``nspec`` number of spectra
    BUNIT  10**-17 erg/(s cm2 Angstrom) str
    ====== ============================ ==== =====================

Data: FITS image [float32, 2881x1031]

HDU15

EXTNAME = Z_IVAR

Inverse variance of flux (1/sigma^2) in units of (10^{-17} erg/s/cm2/A)^-2. Uncertainties comprise statistical uncertainties from the error propagation of the initial CCD pixel variance, the calibration uncertainties, plus an additional term on bright sky lines to account for the imperfect sky subtraction.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ================================= ==== =====================
    KEY    Example Value                     Type Comment
    ====== ================================= ==== =====================
    NAXIS1 2881                              int  ``nwave`` number of wavelengths
    NAXIS2 1031                              int  ``nspec`` number of spectra
    BUNIT  10**+34 (s2 cm4 Angstrom2) / erg2 str
    ====== ================================= ==== =====================

Data: FITS image [float32, 2881x1031]

HDU16

EXTNAME = Z_MASK

Mask of spectral data; 0=good. See the :doc:`bitmask documentation </bitmasks>` page for the definition of the bits.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== ==========================================
    KEY    Example Value Type Comment
    ====== ============= ==== ==========================================
    NAXIS1 2881          int  ``nwave`` number of wavelengths
    NAXIS2 1031          int  ``nspec`` number of spectra
    BZERO  2147483648    int  offset data range to that of unsigned long
    BSCALE 1             int  default scaling factor
    ====== ============= ==== ==========================================

Data: FITS image [int32 (compressed), 2881x1031]

HDU17

EXTNAME = Z_RESOLUTION

Diagonals of z-channel resolution matrix.

Resolution matrix stored as a 3D sparse matrix, modeling the per-fiber non-Gaussian effective line-spread-function resolution. See the :doc:`frame RESOLUTION HDU </DESI_SPECTRO_REDUX/SPECPROD/exposures/NIGHT/EXPID/frame-CAMERA-EXPID>` documentation for details about using this HDU.

Required Header Keywords

.. collapse:: Required Header Keywords Table

    .. rst-class:: keywords

    ====== ============= ==== =====================
    KEY    Example Value Type Comment
    ====== ============= ==== =====================
    NAXIS1 2881          int  ``nwave`` number of wavelengths
    NAXIS2 11            int  ``ndiag`` number of diagonals
    NAXIS3 1031          int  ``nspec`` number of spectra
    ====== ============= ==== =====================

Data: FITS image [float32, 2881x11x1031]

Notes and Examples

The format supports arbitrary channel names as long as for each channel {X} there is a set of HDUs named {X}_WAVELENGTH, {X}_FLUX, {X}_IVAR, {X}_MASK, {X}_RESOLUTION.

For the SURVEY=cmx m33 tile (TILEID=80615) tile and all the SURVEY=sv1 tiles (except TILEID=80971-80976, the dc3r2 ones), proper-motion correction was applied at the :doc:`fiberassign </DESI_TARGET/fiberassign/tiles/TILES_VERSION/TILEXX/fiberassign-TILEID>` design step; thus the following columns can have different values than in the :doc:`desitarget products </DESI_TARGET/TARG_DIR/DR/VERSION/targets/PHASE/RESOLVE/OBSCON/PHASEtargets-OBSCON-RESOLVE-hp-HP>`: TARGET_RA, TARGET_DEC, REF_EPOCH, PLATE_RA, PLATE_DEC, and PLATE_REF_EPOCH.

For targets with a non-zero proper motion, FIBER_RA and FIBER_DEC refer to the position at the reference epoch (but note that the proper-motion correction has been applied at the time of the observation, it is just not recorded in FIBER_RA and FIBER_DEC).