Issues with CCDs that may have affected the quality of DECam observations are recorded on the DECam CCDs page.
DR9sv was a preliminary version of the Legacy Surveys imaging intended to possibly be used for targeting during the DESI Survey Validation (SV) phase. However, DR9sv was never used for DESI SV targeting. Although DR9sv remains publicly available at:
and at NERSC in the directory:
DR9sv has been supplanted by the full DR9 release. We recommend ignoring any data from DR9sv, and using DR9 instead.
After noticing that some bricks that were run using the Cori Burst Buffer at NERSC
were corrupted, we reprocessed all such reductions. A total of 1691 bricks in the
southern region of the Legacy Surveys were
discovered that displayed changes in some of their coadded
files. These bricks were rerun, and assigned a
RELEASE number of
9012 (instead of the
RELEASE number of
9010 used for reductions in the rest of DR9 south of the Legacy Surveys).
A list of the affected bricks is available here.
Blobmodel images were intended to be compressed, and are named with a
.fits.fz suffix, but they are not actually compressed.
x is any of the Legacy Surveys imaging bands) in the Tractor catalogs (and derived
products such as the sweep files) are slightly different from the
NOBS_X quantities in the random catalogs.
The Tractor catalogs
nobs columns count all pixels overlapping each brick pixel, even if the pixel is masked. In contrast,
the random catalogs are derived from the
nexp coadded stacks, which only count pixels where the inverse variances are positive.
This means, for instance, that the
nexp stacks ignore both masked pixels and pixels that have zero weight passed forwards from the
The result of this discrepancy is that a few percent of objects in the Tractor catalogs have different values of
nobs than would
be expected when deriving
NOBS from the same location in the
nexp coadded stacks. Conveniently, the
nobs values in the Tractor catalogs
are (almost) always larger than what would be derived from the
nexp coadded stacks. This means that constraints based on a minimum
in a given filter will always result in reproducible survey geometry, at the expense of rejecting a small fraction (typically <1%) of sources.
A very small number of
ref_id values for Gaia sources appear twice in the Tractor catalogs. One of the duplicates corresponds to the
"correct" Gaia source and the second duplicate has all of the correct information for a Gaia source but with an incorrect
ref_id that would be correct for the second duplicate is missing entirely from the Tractor catalogs.
An example is
ref_id 303293444934132224, which appears in Tractor catalog
tractor-0238p302.fits with correct
information (RA, Dec, etc.) and in Tractor catalog
tractor-0238p305.fits with information that corresponds to
the Gaia source with
The cause of this problem has yet to be fully diagnosed, although the discrepant Gaia sources tend to lie very close to brick boundaries.
This issue will also propagate to the sweep files.