Measured telluric continuum-like opacity beyond 1Â THz

An extensive study of the atmospheric transmission at millimeter and submillimeter wavelengths has been performed since the early 1990s with a Fourier Transform Spectrometer (FTS) mounted on the Caltech Submillimeter Observatory (CSO) atop Mauna Kea (Hawaii), 4100 m above sea level. The goal of these observations is to compile a data base of accurately calibrated atmospheric transmission spectra for use in refining atmospheric models. In this context, the definition of the “quasi-continuum” opacity component is paramount. While our earlier work extending up to 1.0 THz has allowed the separation of the “wet” and “dry” quasi-continua components, with both shown to be following ν2 laws in this regime, here we report on the extension of these observations to 1.6 THz. In the higher frequency regime, our preliminary results indicate that the ν2 description may begin to fail due to proximity to the FIR band centers. Because the opacities in the potentially interesting atmospheric windows at 1.02, 1.35 and 1.5 THz have a large contribution from the quasi-continuum terms, accurate predictions for the transmissions in these windows require refinements in lower frequency models. Comparisons of our data below 1 THz with extant models give a remarkable agreement.