  We conducted the observational tests of a phase correction scheme for the
Atacama Compact Array (ACA) of the Atacama Large Millimeter and submillimeter
Array (ALMA) using the Submillimeter Array (SMA). Interferometers at
millimeter- and submillimeter-wave are highly affected by the refraction
induced by water vapor in the troposphere, which results as phase fluctuations.
The ACA is planning to compensate the atmospheric phase fluctuations using the
phase information of the outermost antennas with interpolating to the inner
antennas by creating a phase screen. The interpolation and extrapolation phase
correction schemes using phase screens are tested with the SMA to study how
effective these schemes are. We produce a plane of a wavefront (phase screen)
from the phase information of three antennas for each integration, and this
phase screen is used for the interpolation and extrapolation of the phases of
inner and outer antennas, respectively. The interpolation scheme obtains
apparently improved results, suggesting that the ACA phase correction scheme
will work well. On the other hand, the extrapolation scheme often does not
improve the results. After the extrapolation, unexpectedly large phase
fluctuations show up to the antennas at the distance of ~140 m away from the
center of the three reference antennas. These direction vectors are almost
perpendicular to the wind direction, suggesting that the phase fluctuations can
be well explained by the frozen phase screen.
