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A major error in the data observed at submillimter wavelengths is the phase distortion and
amplitude attenuation
due to the airmass in the atmosphere. The system temperature (T)
measurements determined by comparing the receiver output power from an
ambient temperature load with that of the sky are essential to tracking
amplitude attenuation variations. Therefore, the system temperature (T)
can be used to correct for the gains in amplitude.
No system temperature corrections have been applied to the SMA archival data.
However the frequently measured T values for each antenna are
stored in the header of SMA archival data for each pair of antennas under
the baseline file bl_read. The antenna-based T are computed
and stored in the header of uvdata in Miriad by smalod. The measured
T is used to calibrate the atmosphere attenuation in the
visibility amplitudes.
Jun-Hui Zhao (miriad for SMA)
2012-07-09