Background

WFCAM (see http://www.roe.ac.uk/atc/projects/wfcam/index.html) will enable the next generation wide-angle sky survey to be undertaken in the UK. It follows on from the hugely successful UK Schmidt photographic surveys of the last decades of the twentieth century, the major difference between the old and the new being the data rates and volumes that will be produced. WFCAM employs 4 2k$\times$2k Rockwell devices and has an instantaneous field-of-view of 0.21 square degrees. WFCAM is expected to be on-telescope for the greater fraction of all available UKIRT time, and will have average/peak data rates of 100/230 Gbytes per night. It will commence operations in the final quarter of 2003.

There is, of course, a clear need for 4m survey facilities in the era of 8m-class telescopes; the relative performance of WFCAM (as measured by its `grasp', or information gathering product A$\Omega$) shows (see, for example, the original VISTA science case, available from http://www.vista.ac.uk/) that it is amongst the world's leading IR survey instruments, even when including other non-dedicated survey facilities such as VLT-IRMOS. The combined science case (for complete details, follow the URL http://www.ukidss.org/sciencecase/sciencecase.html) proposed by the UKIDSS consortium for WFCAM, for example, details a programme that is unrivalled in terms of depth, field of view and therefore survey volume. UKIDSS proposes a nested series of surveys ranging from the Large Area Survey (`LAS', 4000 sq. deg. to K=18.4), the Galactic Plane Survey (`GPS', 1800 sq. deg. to K=19), the Galactic Clusters Survey (`GCS', 1600 sq. deg. to K=18.7), the Deep Extragalactic Survey (`DXS', 35 sq. deg. to K=21) to the Ultra-Deep Survey (`UDS', 0.8 sq. de.g. to K=23). The image data alone for these amounts to $\sim50$ Tbytes of data, while the object catalogue and ancillary information are likely to be many Tbytes in size.