Amplitude Correction and System Temperature

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$_{\rm sys}$) 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$_{\rm sys}$) 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$_{\rm sys}$ 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$_{\rm sys}$ are computed and stored in the header of uvdata in Miriad by smalod. The measured T$_{\rm sys}$ is used to calibrate the atmosphere attenuation in the visibility amplitudes.