The essential components of SuperCOSMOS consist of a granite air-bearing xy table providing high-accuracy position measurements, a linear CCD array (of 2048 pixels) producing the high-speed scanning capability, and transputers and DEC Alpha workstations for rapid data processing.
The scan of a plate is made up of "strips", where the width of a strip is equivalent to the length of the CCD, or the part of the CCD used (currently 1280 pixels or 12.8 mm). Scanning is accomplished by shining a beam from a light source (currently a tungsten halogen lamp, which is soon to be replaced by a Xenon arc lamp) through the photographic plate and allowing the light transmitted to be collected by the CCD. The system, therefore is a multiplex detector, recording 1280 pixels simultaneously. For each strip being recorded, the plate is moved under the CCD in 1 direction (the y direction) by the xy table, while the CCD array provides the scan in the other (x) direction. When the top of the plate is reached, the table is stepped in x by 1 scan-width ready for the next strip and the process is repeated. The scan of a complete Schmidt plate is performed in under 2 hours producing some 2 Gbytes of pixel data. These pixel data are routinely archived on high-capacity tape sub-systems for subsequent further analysis.
The transputers control all low-level tasks of the system:- table positioning, dynamical focussing, light-level monitoring, data acquisition, etc. The operator communicates with the system through a menu-driven graphical interface running on the master computer workstation (Digital Alphastation). All high-level data processing is performed off-line on dedicated Alphastations.
The entire system is housed in an environmental chamber, providing class 100 clean-room conditions and strict thermal stability (temperature maintained to +/- 0.05 degrees centigrade over a 24 hour period) thus ensuring strict integrity of the data during the scan process.
- High scanning speed;
- High scanning resolution;
- High positional accuracy;
- High dynamic range;
- High data integrity;
- High system reliability.