A real-time parallel-processing imaging system for radio astronomy

ACSIS (Auto Correlation Spectrometer Imaging System) is a real-time data collection and reduction system intended for use with a 16 pixel receiver at the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. At peak operating speed, the correlator connected to each receiver will generate an autocorrelation lag array of 8192 numbers every 50 ms, or 10.5 Mbytes of data every second. The ACSIS reduction system converts raw lag-data into calibrated radio-frequency spectra as the data are obtained. In mapping modes, these spectra are further inserted into a 3-dimenslonal data cube of image planes as a function of radio frequency. The reduction system should produce calibrated data of sufficient quality that further o-line processing is not required. Since single dish radio telescopes can observe the sky in many different ways, the reduction system has been effectively designed as a collection of high-performance programmable calculators that can be easily reconfigured for different or new observing modes. We describe the object-oriented design of the system and present some initial timing results obtained from processing synthetic data on a small Beowulf cluster of sixteen 450-MHz commodity PCs. The astronomer can view the data as it is processed by a data display that shows both the radio spectra and the contents of the gridded data cubes as they are updated.