Processing and Calibration of Submillimeter Fourier Transform Radiometer Spectra From the RHUBC-II Campaign

The Radiative Heating in Underexplored Bands Campaign-II, conducted in 2009 from a high-altitude site in northern Chile, combined ground-based radiometry with radiosonde measurements of atmospheric state, for the purpose of testing atmospheric radiation models under conditions strongly influenced by water vapor in the middle to upper troposphere. A suite of broadband Fourier transform spectrometers (FTSs) measured the entire terrestrial thermal radiance spectrum from 1000- to 3.3- \mu\hbox{m} wavelength. The submillimeter portion of the spectrum, from 1000 to 85 \mu\hbox{m} (300-3500 GHz) was covered by a polarizing FTS referred to as the Smithsonian Astrophysical Observatory (SAO) FTS. Here, we describe data processing and radiometric calibration algorithms for this instrument. These include correction of interferograms for periodic sampled lag error, development of a temperature-dependent instrument calibration model, and principal component analysis of the complete set of spectra acquired during the campaign.