  The Wide-field Imaging Interferometry Testbed (WIIT) was designed to
validate, experiment with, and refine the technique of wide field mosaic
imaging for optical/IR interferometers. Here we offer motivation for WIIT,
present the testbed design, and describe algorithms that can be used to reduce
the data from a spatial and spectral Michelson interferometer. A conventional
single-detector Michelson interferometer operating with narrow bandwidth at
center wavelength lambda is limited in its field of view to the primary beam of
the individual telescope apertures, or ~lambda/d radians, where d is the
telescope diameter. Such a field is too small for many applications; often one
wishes to image extended sources. We are developing and testing techniques
analogous to the mosaicing method employed in millimeter and radio astronomy,
but applicable to optical/IR Michelson interferometers, in which beam
combination is done in the pupil plane. An Npix x Npix array detector placed in
the image plane of the interferometer is used to record simultaneously the
fringe patterns from many contiguous telescope fields, effectively multiplying
the field size by Npix/2, where the factor 2 allows for Nyquist sampling. This
technique will be especially valuable for interferometric space observatories,
such as the Space Infrared Interferometric Telescope (SPIRIT) and the
Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). SPIRIT and
SPECS will be designed to provide sensitive, high angular resolution,
far-IR/submillimeter observations of fields several arcminutes in diameter, and
views of the universe complementary to those provided by the Hubble Space
Telescope (HST), the Next-Generation Space Telescope (NGST), and the Atacama
Large Millimeter Array (ALMA).
