How much data will Pan-STARRS produce?
Each raw image from a single Pan-STARRS camera will contain 2
Gbytes (2 bytes per pixel). In full survey mode, typical exposures
last 30 seconds, so the raw data rate is several terabytes per
night for the full telescope. The amount of data produced by Pan-STARRS
is so large that it will not be practical to archive every image.
Software techniques are therefore being developed to extract
the important information from the images, while allowing less
crucial information to be discarded.
What kind of data reduction will be necessary?
As soon as a Pan-STARRS image is read out, it must be
searched for known stars, which are then used to calibrate the image
both astrometrically and photometrically. The images from the four
cameras are then compared with each other to remove spurious
effects such as cosmic rays, gaps between CCD cells, and bad pixels,
and a composite image is calculated based on the four subimages
and corrected for measured variations in atmospheric seeing. The
composite image is then used in three ways:
First, so long as it passes quality control, it is added
to a master image of the sky that is being built up week by week.
As the total amount of observing time grows, this cumulative image
will have a better and better signal to noise ratio. The cumulative
sky image is particularly important for studies of distant galaxies
and clusters of galaxies, which are faint, but which are not expected
to move or vary.
Second, each composite image will be subtracted from a master image made from earlier observations of the same part of the sky taken with the same filter.
Stationary, unvarying objects should cancel out, leaving only those
objects which have moved or changed their brightness. The positions
and magnitudes of these objects will then be measured and added to a database.
Some of them will be known moving or varying objects, others will
be new discoveries, the most interesting of which will be reported
to the Pan-STARRS staff for further study or action.
Third, each composite image will be digitally scanned and the
positions and magnitudes of all objects above a threshold brightness
will be stored in a database for future reference.
Finally the composite image, as well as the four
individual telescope images, will normally be discarded, freeing
up storage space for future images.
Given the speed at which Pan-STARRS produces new images, all the
above steps must be completed within about one minute of computer
time.
Where will the data be reduced and stored?
Data will be reduced and stored at a sea-level computing facilty consisiting of a large array of realatively simple PCs. The data will be sent down from the observatory by fiber optic link.
Will the data be publicly accessible?
The "3π" deep and ultradeep
surveys will be accessible to the public after completion, as will
catalogs of moving, variable, and transient objects discovered by
Pan-STARRS.
Next: PS1 Prototype
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