Atmospheric Phase Correction Using Total Power Radiometry at the Submillimeter Array

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° to 27° over a 20 minute period with a 2.5 s integration time. This corresponds to a residual differential electrical path of 98 μm, or 15 μm of precipitable water vapor, and raises the coherence in the 20 minute period from 0.45 to 0.9.