Legacy Survey Files

Top level directory for web access:: http://portal.nersc.gov/cfs/cosmo/data/legacysurvey/dr1/
Top level directory local to NERSC computers (for collaborators):: /global/cfs/cdirs/cosmo/data/legacysurvey/dr1/

Summary Files

decals-bricks.fits

FITS binary table with the RA, DEC bounds of each geometrical "brick" on the sky. The subset of bricks which have g-, r-, or z-band imaging in this data release can be identified using the has_image_g, has_image_r, and has_image_z tags, respectively. The bricks with a corresponding Tractor photometric catalog in this release can be identified using the has_catalog tag.

HDU1 (only HDU) - tags in the decals-bricks.fits file

Column	Type	Description
`brickname`	char[8]	Name of the brick.
`brickid`	int32	A unique integer with 1-to-1 mapping to `brickname`.
`brickq`	int16	A "priority" factor used for processing.
`brickrow`	int32	Dec row number.
`brickcol`	int32	Number of the brick within a Dec row.
`ra`	double	RA of the center of the brick.
`dec`	double	Dec of the center of the brick.
`ra1`	double	Lower RA boundary.
`ra2`	double	Upper RA boundary.
`dec1`	double	Lower Dec boundary.
`dec2`	double	Upper Dec boundary.
`has_image_g`	byte	This brick has imaging data in this band.
`has_image_r`	byte	This brick has imaging data in this band.
`has_image_z`	byte	This brick has imaging data in this band.
`has_catalog`	byte	This brick has Tractor photometry.

decals-ccds.fits

Column	Type	Description
`filter`	char[1]
`ra`	double
`dec`	double
`airmass`	float
`date_obs`	char[26]
`g_seeing`	float
`exptime`	float
`expnum`	int32
`mjd_obs`	float
`propid`	char[10]
`guider`	int32
`object`	char[31]
`avsky`	float
`arawgain`	float
`fwhm`	float
`crpix1`	double
`crpix2`	double
`crval1`	double
`crval2`	double
`cd1_1`	float
`cd1_2`	float
`cd2_1`	float
`cd2_2`	float
`extname`	char[8]
`ccdnum`	int32
`cpimage`	char[82]
`cpimage_hdu`	int32
`calname`	float[38]
`height`	int32
`width`	int32
`ra_bore`	double
`dec_bore`	double
`dr1`	byte

FITS binary table with almanac information (seeing, sky-brighness, etc.) about each individual CCD image. The subset of CCDs included in this release can be identified using the DR1 tag.

decals-specz.fits

Merged photometric and spectroscopic catalog for 751,070 sources with spectroscopic redshifts from SDSS/DR12. This file is a binary FITS table with 4 extensions (HDUs). Each extension contains the following row-matched catalogs:

HDU1 - DECaLS photometry and related Tractor outputs, WISE forced photometry (http://unwise.me)

Column	Type	Description
`brickid`	int32	Name of the brick.
`brickname`	char[8]	A unique integer with 1-to-1 mapping to `brickname`.
`objid`	int32
`brick_primary`	char[1]
`blob`	int32
`type`	char[4]
`ra`	double
`ra_ivar`	float
`dec`	double
`dec_ivar`	float
`bx`	float
`by`	float
`bx0`	float
`by0`	float
`left_blob`	char[1]
`decam_flux`	fltarr[6]
`decam_flux_ivar`	fltarr[6]
`decam_apflux`	fltarr[48]
`decam_apflux_resid`	fltarr[48]
`decam_apflux_ivar`	fltarr[48]
`decam_mw_transmission`	fltarr[6]
`decam_nobs`	bytarr[6]
`decam_rchi2`	fltarr[6]
`decam_fracflux`	fltarr[6]
`decam_fracmasked`	fltarr[6]
`decam_fracin`	fltarr[6]
`out_of_bounds`	char[1]
`decam_anymask`	intarr[6]
`decam_allmask`	intarr[6]
`wise_flux`	fltarr[4]
`wise_flux_ivar`	fltarr[4]
`wise_mw_transmission`	fltarr[4]
`wise_nobs`	intarr[4]
`wise_fracflux`	fltarr[4]
`wise_rchi2`	fltarr[4]
`dchisq`	fltarr[4]
`fracdev`	float
`fracdev_ivar`	float
`shapeexp_r`	float
`shapeexp_r_ivar`	float
`shapeexp_e1`	float
`shapeexp_e1_ivar`	float
`shapeexp_e2`	float
`shapeexp_e2_ivar`	float
`shapedev_r`	float
`shapedev_r_ivar`	float
`shapedev_e1`	float
`shapedev_e1_ivar`	float
`shapedev_e2`	float
`shapedev_e2_ivar`	float
`ebv`	float

HDU2 - SDSS/DR12 spectroscopy (http://data.sdss3.org/sas/dr12/sdss/spectro/redux/specObj-dr12.fits )
HDU3 - SDSS/DR12 photometry (http://data.sdss3.org/sas/dr12/sdss/spectro/redux/photoPosPlate-dr12.fits)

ZeroPoints-DR1.fits

The ZeroPoints-DR1.fits file contains information regarding the photometric and astrometric zero points for each CCD of every DECam image that is part of the DECaLS DR1 data release. Photometric zero points for each CCD are computed by identifying stars and comparing their instrumental magnitudes (measured in an approximately 7 arcsec diameter aperture) to color-selected stars in the PanSTARRS "qy" catalog.

HDU1 (only HDU) - tags in the ZeroPoints-DR1.fits file

Column	Type	Description
`filename`	char[78]	Name of the NOAO CP-reduced image FITS file.
`expnum`	char[12]	Unique DECam exposure number.
`exptime`	float	Exposure time in seconds.
`filter`	char[32]	Filter used for observation.
`seeing`	float	Seeing in arcseconds determined by fitting a 2-dimensional gaussian to the median PSF of stars on the CCD.
`ra`	double	Right Ascension in decimal degrees.
`dec`	double	Declination in decimal degrees.
`zpt`	float	Median zero point for the entire image (median of all CCDs of the image).
`ccdnum`	int32	CCD number (see DECam layout).
`ccdname`	char[3]	CCD name (see DECam layout).
`ccdra`	double	Central RA for the CCD.
`ccddec`	double	Central Dec for the CCD.
`ccdzpt`	double	Zeropoint for the CCD (AB mag).
`ccdphrms`	double	Photometric rms for the CCD (in mag).
`ccdskyrms`	double	Sky rms (in counts).
`ccdraoff`	double	Median astrometric offset for the CCD <PS1-DECaLS> in arcsec.
`ccddecoff`	double	Median astrometric offset for the CCD <PS1-DECaLS> in arcsec
`ccdnstar`	int32	Number of stars found on the CCD.
`ccdnmatch`	int32	Number of stars matched to PS1 (and used to compute the photometric zero points and astrometric offsets).
`ccdmdncol`	float	Median (g-i) color from the PS1 catalog of the matched stars.
`dr1`	byte	Included in the DR1 data set? 1=Yes, 0=No. Images that are non-photometric or on malfunctioning CCDs are excluded from DR1.

Tractor Catalogs

tractor/<AAA>/tractor-<brick>.fits

FITS binary table containing Tractor photometry, documented here: http://legacysurvey.org/dr1/catalogs/.

Sweep Catalogs

tractor-sweep-<AAA>.fits

Light-weight FITS binary tables (containing a subset of the most commonly used Tractor measurements) of all the Tractor catalogs in a given degree of right ascension <AAA>.

Image Stacks

coadd/<AAA>/<brick>/decals-<brick>-ccds.fits

FITS binary table with the list of CCD images that were used in this brick. EXPNUM indicates the DECam exposure ID and FILTER indicates the filter (u,g,r).

coadd/<AAA>/<brick>/decals-<brick>-image-<filter>.fits

Stacked image centered on a brick location covering 0.25° × 0.25°. The primary HDU contains the coadded image (simple unweighted coadd), in units of nano-maggies per pixel.

NOTE: These are not the images used by Tractor, which operates on the single-epoch images.

coadd/<AAA>/<brick>/decals-<brick>-invvar-<filter>.fits

Corresponding stacked inverse variance image based on the sum of the inverse-variances of the individual input images in units of 1/(nano-maggies)² per pixel.

NOTE: These are not the inverse variance maps used by Tractor, which operates on the single-epoch images.

coadd/<AAA>/<brick>/decals-<brick>-model-<filter>.fits.gz

Stacked model image centered on a brick location covering 0.25° × 0.25°.

The Tractor's idea of what the coadded images should look like; the Tractor's model prediction.

coadd/<AAA>/<brick>/decals-<brick>-chi2-<filter>.fits

Stacked χ² image, which is approximately the summed χ² values from the single-epoch images.

coadd/<AAA>/<brick>/decals-<brick>-depth-<filter>.fits.gz

Stacked depth map in units of the point-source inverse-variance at each pixel.

The 5σ point-source depth can be computed as 5 / sqrt(depth_ivar) .

coadd/<AAA>/<brick>/decals-<brick>-nexp-<filter>.fits.gz

Number of exposures contributing to each pixel of the stacked images.

coadd/<AAA>/<brick>/decals-<brick>-image.jpg

JPEG image of calibrated image using the g,r,z filters as the colors.

coadd/<AAA>/<brick>/decals-<brick>-model.jpg

JPEG image of the Tractor's model image using the g,r,z filters as the colors.

coadd/<AAA>/<brick>/decals-<brick>-resid.jpg

JPEG image of the residual image (data minus model) using the g,r,z filters as the colors.

Raw Data

See the raw data page.