  Phase noise caused by an inhomogeneous, time-variable water vapor
distribution in our atmosphere reduces the angular resolution, visibility
amplitude and coherence time of millimeter and submillimeter wavelength
interferometers. We present early results from our total power radiometry phase
correction experiment carried out with the Submillimeter Array on Mauna Kea.
  From accurate measurements of the atmospheric emission along the lines of
sight of two elements of the array, we estimated the differential atmospheric
electrical path between them. In one test, presented here, the phase correction
technique reduced the rms phase noise at 230 GHz from 72$\degr$ to 27$\degr$
over a 20 minute period with a 2.5 second integration time. This corresponds to
a residual differential electrical path of 98 $\mu$m, or 15 $\mu$m of
precipitable water vapor, and raises the coherence in the 20 minute period from
0.45 to 0.9.
