Platform Deformation Phase Correction for the AMiBA-13 Co-planar
  Interferometer
  We present a new way to solve the platform deformation problem of co-planar
interferometers. The platform of a co-planar interferometer can be deformed due
to driving forces and gravity. A deformed platform will induce extra components
into the geometric delay of each baseline, and change the phases of observed
visibilities. The reconstructed images will also be diluted due to the errors
of the phases. The platform deformations of The Yuan-Tseh Lee Array for
Microwave Background Anisotropy (AMiBA) were modelled based on photogrammetry
data with about 20 mount pointing positions. We then used the differential
optical pointing error between two optical telescopes to fit the model
parameters in the entire horizontal coordinate space. With the platform
deformation model, we can predict the errors of the geometric phase delays due
to platform deformation with given azimuth and elevation of the targets and
calibrators. After correcting the phases of the radio point sources in the
AMiBA interferometric data, we recover 50% - 70% flux loss due to phase errors.
This allows us to restore more than 90% of a source flux. The method outlined
in this work is not only applicable to the correction of deformation for other
co-planar telescopes but also to single dish telescopes with deformation
problems. This work also forms the basis of the upcoming science results of
AMiBA-13.
