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E. Serabyn, J. Pardo (Caltech)
Absolute brightness temperature measurements of the giant planet atmospheres at submillimeter wavelengths remain hard to come by. However, the continuum brightness level in this spectral region is sensitive to the NH3 and PH3 mixing ratios, vertical profiles, and line-wing shapes. Therefore, we have been carrying out a series of measurements aimed at producing well calibrated brightness temperature spectra. To this end, we have been making spectral measurements of the giant planets with our Fourier Transform Spectrometer (FTS) at the Caltech Submillimeter Observatory. After some experimentation, it was found that several calibration steps are necessary in order to produce fully calibrated spectra, including a 2-step correction for atmospheric absorption (the first step being the standard ``planet-sky/hot-sky" calibration, and the second step a correction for our own atmosphere's vertical lapse rate determined from an atmospheric transmission curve measured with the same FTS), and a beam coupling model for coupling to planets of different sizes. The atmospheric correction was first tested on the Moon, and found to yield very flat brightness temperature spectra, thus validating the 2-step correction. Using also the appropriate beam coupling model, we have also produced our first fully calibrated brightness temperature spectrum of Saturn over approximately the 300 - 700 GHz range at a resolution of about 3 GHz. Data on Jupiter are also in hand.