The DR7 contains that part of the SDSS imaging and spectroscopy
taken through July 14, 2008. Here we give coverage plots and the
detailed coverage tables from which they were
constructed, though excluding the supplemental imaging scans released
through DRsup. Further below, we
outline the future sky coverage of SDSS. The
survey terms are explained in the sections on imaging coverage and spectroscopic coverage below.
For data interfaces, see the data
Anomalies in the DR7 Footprint
Several stripes, when
examined in detail, have anomalies (or errors) in the definition of the
PRIMARY (mode = 1) footprint. Usually objects which should be in the
primary footprint are missing. The links
here provide a guide to the anomalies on a stripe-by-stripe basis, and
in most cases, show sample SQL query clauses in which may be executed
on the RunsDB database in order to recover objects uniquely
within the full DR7 footprint.
Known anomalies in stripe:
Anomalies in the Astrometry
The quoted astrometric errors for SDSS are about 100 mas per coordinate or
better, on average, around the sky. To check this, we have compared
the positions of objects between the SDSS catalog and the 2MASS catalog,
adn between the SDSS and the USNO-NOMAD catalogs, and we find a few
positions within the SDSS footprint, especially some scans at high
declination, where the errors are larger than the nominal values.
In the following link we provide are some information about these
astrometry anomalies, and how to find them.
SDSS DR7 Footprint Summary
Open and Globular Clusters
DR7 includes spectroscopy of stars in 12 open and globular clusters
to calibrate the measurements of stellar parameters in SEGUE (Lee
Many of these clusters are sufficiently close that
the giant branches are brighter than the photometric saturation limit
of SDSS, so the targets for these plates were selected from the
literature. Indeed, the spectrographs would saturate as well with our
standard 15-minute exposures, so these observations had individual
exposure times as short as one or two minutes. Without proper flux
calibrators or exposure of bright sky lines to set the zeropoint of
the wavelength scale, the spectrophotometry and wavelength calibration
of the spectra on these plates are often quite inferior to that of the
main survey, and these plates are available only in the DAS, not the
Repeat scans of the Celestial Equator
The 2.5º stripe centered on the Celestial Equator (stripe 82) was
imaged multiple times throughout SDSS and SDSS-II. Each 2.5º
wide stripe is observed by a pair of offset strips to cover the full
width. DR7 contains data from the individual runs, including those
taken under non-ideal conditions, and a deep coadd of a subset of the
For reference, the coverage tables describe the sky coverage in
terms of survey coordinates. To translate the sky coverage into
celestial coordinates, please refer to the coordinates
section of the EDR paper and the description below.
Note: The coverage tables, and a number of other
files we distribute, are given as ASCII parameter (.par) files.
||atStripeDef.par (survey coordinates) Including SEGUE stripe defs
||All DAS Runs Link to all runs in the DR7 DAS
||AllCASRuns.dr7.par All scanline segments in the DR7 CAS
||tsChunk.dr7.best.par (great circle
coordinates) - see Target and
||tsChunk.dr7.target.par (great circle
coordinates) - see Target and
||SEGUERuns.dr7.par List of SEGUE scanline segments
||Stripe82.dr7.par Stripe 82 scanline segments; see SN DR7
||RunsDB.dr7.par List of scanline segments in Runs DB
||DR7 contains additional plates beyond the main survey plates:
"extra" plates which are reobservations of main survey
plates; "special" plates which take spectra beyond the
main survey targets, and "extraspecial" reobservations of
special plates. There is a separate page descriging the special plates.There are
5 coverage files: one for all the plates, and 4 for each of the
The coverage files give plate centers by plate
number and MJD of observation.
Note also the list of list of quality
"holes" (small areas of bad seeing etc.) and missing data, the list of fields which are missing only
apparently (e.g., data from different runs were used in target and
best) and the list of differences in sky
coverage between target and best.
Imaging coverage: stripes, runs, reruns
The survey coverage is defined in survey
coordinates, as described in the coordinates
section of the EDR paper. For detailed astrometry please see the
following note about parts
of the survey which have a slightly different survey coordinate system
from the rest.
The imaging survey scans the sky along great circles, which are
circles of constant survey latitude eta. Scans are obtained
along stripes spaced 2.5° in survey latitude. Each stripe
has an integer stripe number n such that the inclination of a
stripe with respect to the celestial equator is -25° + 2.5°
× n. The boundaries of the region eventually to be
surveyed by the SDSS are defined in terms of survey longitude
lambda in atStripeDef.par.
Runs cover strips, two strips cover a stripe
An imaging run designates a continuous scan of the imaging
telescope. The survey camera's focal plane has six
columns of CCDs, so that a single run consists of six camera
columns (camcols) (see the instrument descriptions). The
camera columns have a gap which is filled by an offset second run. The
six camcols taken together are called a strip. Thus
to completely cover the two strips making up one
stripe, at least two runs are required. The imaging
data reduction is done on a run-by-run basis, hence the imaging data in our Data Archive are accessible by run
Great circle coordinates
Every stripe has its own great circle
coordinate system. The coordinate along a great circle is called
mu. The range of data
actually obtained for a given stripe is reported in terms of
a range in great circle mu along that stripe as
startMu and endMu
in the coverage tables above. Both startMu
and endMu are given in integer
The calibrated object lists are accessible in the archive by stripe
number and startMu on that stripe.
For historical reasons, DR1 contained both photometric and
spectroscopic data which lay outside the official survey limits, i.e.,
the startMu/endMu for some runs extend beyond the
lambda limits for the stripes they cover. Since DR3,
target data in those areas are still marked
non-primary, but the
best data are primary. Please
refer to this note about DR7 data
outside the SDSS survey area for details on how to retrieve
A run is divided into images 2048 pix × 1361 pix
which are called fields. Each field then has the first 128
rows of the following field attached to it, so that all survey images
actually have a size of 2048 pix × 1489 pix.
Object detection, photometry and classification are done field by
field. In particular, the calibrated object lists and
survey images are
distributed separately for each field. To account for the overlap, object
detection is not performed on the first 64 rows or the last 64 rows of
each corrected frame.
Note that one therefore should use only objects in
the "primary" area of
each survey field, in order to avoid duplicate area and duplicate
object detections. Near the center of a stripe, the primary area will
be the full 2048 pix × 1361 pix, but frames overlap near the
ends of stripes, reducing the primary area there. Please refer to how
"primary" is set in
the "status" flag of an object and please also see the details of
how overlapping areas are
resolved. The primary area of each field is recorded as entry
stripeArea in the tsField*.fit file
Every time we (re)process our imaging data, we assign the outputs a
new rerun number. Thus, a rerun does not imply
re-observation, but is simply a re-reduction of the same run.
The re-reduction can use more recent software or calibrations than a
previous rerun, or both. Across runs, the rerun is an arbitrary
index, so the same rerun of different runs does not have to be
produced with the same software or calibrations.
Target and Best
We publish two reruns for each run:
There is one coverage table each for the target and best version. The
tables contain the following information:
- A target rerun, which is the reduction used to select
targets for the spectroscopic survey. This is referred to as
skyVersion = 0.
- A best rerun, which is the best available
reduction. This is usually a different rerun from the
target version, since our photometric pipelines have
been evolving. The best rerun is referred to as
skyVersion = 1. All best reruns
have rerun >=40.
- The survey area on the sky, given as a stripe number
and a range for the mu coordinate (
<= mu <=
endmu). These were used
to create the plots above.
- The runs and reruns and the range of
fields which cover the given area. This is the
information needed to find data for a given part of the sky in
the Data archive.
The spectrograph's 640 fibers are distributed on a plug plate of
roughly 3° diameter (7 square degree area) projected on
sky. Spectroscopic coverage is given in terms of the plate centers.
Plates are identified by a unique number assigned during targetting
and the MJD on which they were observed, to distinguish
re-observations of the same plate.
Incremental sky coverage of SDSS
A map of the incremental coverage of the numbered Data Releases (i.e.,
excluding the EDR) by DR number.
Future sky coverage of SDSS
Imaging of the Southern Galactic hemisphere and further spectroscopy
is continuing as part of
*Text and figures on this page come from an author-created, un-copyedited
version of the SDSS Data Release 7 paper, an article submitted
to Astrophysical Journal Supplements. IOP Publishing Ltd is not responsible for any errors
or omissions in this version of the manuscript or any version derived from it. A preprint of the
DR7 paper is available from the arXiv preprint server.
Last modified: Sat Sep 15 01:51:39 CEST 2007