Sky coverage
The DR1 contains that part of the SDSS imaging and spectroscopy taken before such and such a date satisfying the survey quality
requirements do we have a link to
those?. Here we give coverage plots and the detailed coverage tables from which they were
constructed. The survey terms are explained in the sections on imaging coverage and spectroscopic coverage below.
Also check the SDSS finding chart for
survey coverage.
Coverage tables
Note also the list of list of quality
"holes" and missing data.
Imaging coverage: stripes, runs, reruns
Since the imaging survey scans along great circles on the sky, the
survey coverage is defined in great
circle coordinates. Great circles are labelled by an integer
stripe number n such that the inclination of a stripe with
respect to the celestial equator is -25° + 2.5° ×
n. The coordinate along a stripe is called mu. The DR1
coverage is therefore defined in terms of stripe number and
mu.
An imaging run designates a continuous scan of the imaging
telescope along a stripe. Since the camera's focal plane is not
completely filled with CCDs (see the instrument descriptions), at
least two runs are required to completely cover one stripe.
A single run's contribution is called a strip. The imaging
data reduction is done on a run-by-run basis, hence the data in our Data Archive are accessible by run
number. A run is divided into images 2048 pix × 1489
pix which are called fields. Object detection, photometry
and classification is done field by field.
Every time we (re)process our imaging data, we assign the outputs a
new rerun number. Across runs, this is an arbitrary index, so
the same rerun of different runs does not have to be produced with the
same software or calibrations.
We publish two reruns for each run
contained in DR1:
- 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 .
There is one coverage table each for the target and best version. The
tables contain the following information:
- The survey area on the sky, given as a stripe number
and a range for the mu coordinate (
startmu
<= 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.
Notes
Spectroscopy
The spectrograph's 640 fibers are distributed on a plug plate of
roughly 7° diameter 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.
The file above defines the DR1 spectroscopic coverage. There is an
ASCII plate summary listing all
plates together with the numbers of objects of various categories
found.
Last modified: Mon Mar 3 15:23:53 CST 2003
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