New astronomical surveys almost invariably herald advances in
astrophysics. Surveys play a crucial role in identifying new classes
of objects, in revealing structure in the Universe, and in expediting
studies of individual objects. Each new generation of instrumentation
usually warrants a new survey. Hence the ROSAT Sky Survey replaces the
HEAO-I Sky Survey, the 2MASS survey (Kleinmann 1992)
will replace the AFGRL survey, etc.
Since radio
telescopes tend to be unique, there are few matched surveys in
the northern and southern hemispheres. The only reasonably uniform
sky survey in the radio band is the
5 GHz survey carried out at Greenbank and Parkes; it
is the best existing radio survey, with a limiting
flux density of mJy and positional accuracy of
arcmin. Both the relatively high flux density limit and the
relatively large positional uncertainty limit the
usefulness of this 5 GHz database. With this in mind, the National Radio
Astronomy Observatory (NRAO) has decided
to utilize the VLA to produce a next generation radio sky survey.