FTS measurements of submillimeter-wave atmospheric opacity at Pampa la Bola II : Supra-terahertz windows and model fitting

Abstract

A second observing run aimed to measure the millimeter and submillimeter-wave (150-1500 GHz or 2 mm-200 μm) atmospheric opacity was carried out with a Fourier Transform Spectrometer (FTS) at Pampa la Bola, 4800 m above sea level in northern Chile. We obtained high transmission spectra, showing up to ∼ 67% transmission at submillimeter-wave windows. The observed spectra can be well modeled by newly developed radiative-transfer calculations. Correlations between 220 GHz and submillimeter-wave opacities were reanalized, including the new data set. The results show almost identical trends as the ones resulting from the first measurements. We also identified supra-terahertz windows (located around 1035 GHz, 1350 GHz, and 1500 GHz), which could not be seen in our first measurements. Opacity correlations between the 220 GHz and these new windows are derived for the first time. Combined with a statistical study of the 225 GHz opacity data of the Chajnantor site (7 km apart from Pampa la Bola), it is estimated that submillimeter-wave observations can be done with zenith opacity less than 1.0 (at the most transparent frequency in those windows) for about 50% of the winter season.