Dream, the Dutch Real-time Acquisition Mode for Scuba

In order to improve the eeciency with which SCUBA (see elsewhere in this conference) operates on the JCMT , a new and innovative data acquisition system has been developed and will be implemented shortly. The fundamental innovation is in the operation of the telescope secondary mirror, merging the function of chopping for sky-elimination, and 'jiggling' to sub-pixel positions to Nyquist sample the image as seen by the arrays themselves. This eliminates the need to sample 'empty sky' for half the time, thus doubling the time spent 'on target'. Additional expected advantages are :-improved sky suppression and :-increased dynamic range in the resulting image. It is hoped that the target of shotnoise limited performance will prove within reach.