Intensity and polarization of the atmospheric emission at millimetric wavelengths at Dome Concordia

Abstract

Atmospheric emission is a dominant source of disturbance in ground-based astronomy at millimetric wavelengths. The Antarctic plateau is recognized as an ideal site for millimetric and submillimetric observations, and the French/Italian base of Dome Concordia (Dome C) is among the best sites on Earth for these observations. In this paper, we present measurements at Dome C of the atmospheric emission in intensity and polarization at a 2-mm wavelength. This is one of the best observational frequencies for cosmic microwave background (CMB) observations when considering cosmic signal intensity, atmospheric transmission, detector sensitivity and foreground removal. Using the B-mode radiation interferometer (BRAIN)-pathfinder experiment, we have performed measurements of the atmospheric emission at 150 GHz. Careful characterization of the airmass synchronous emission has been performed, acquiring more than 380 elevation scans (i.e. 'skydip') during the third BRAIN-pathfinder summer campaign in 2009 December/2010 January. The extremely high transparency of the Antarctic atmosphere over Dome C is proven by the very low measured optical depth, <τI>= 0.050 ± 0.003 ± 0.011, where the first error is statistical and the second is the systematic error. Mid-term stability, over the summer campaign, of the atmosphere emission has also been studied. Adapting the radiative transfer atmosphere emission model am to the particular conditions found at Dome C, we also infer the level of the precipitable water vapor (PWV) content of the atmosphere, which is notoriously the main source of disturbance in millimetric astronomy (? mm). Upper limits on the airmass correlated polarized signal are also placed for the first time. The degree of circular polarization of atmospheric emission is found to be lower than 0.2 per cent [95 per cent confidence level (CL)], while the degree of linear polarization is found to be lower than 0.1 per cent (95 per cent CL). These limits include signal-correlated instrumental spurious polarization

Global Distribution of Water Vapor and Cloud Cover—Sites for High-Performance THz Applications

“…a reported median PWV at Dome C three times greater in reference [4] versus [15] due to different observation periods and methods. Nonetheless, MOD07 PWV measurements match the same qualitative trend as site-specific measurements.…”

“…These sites were individually located and often painfully characterized, focusing on astronomical observatories and often over short periods of time [1][2][3][4][5][6]. Satellite data has been used in these studies, over small regions and with limited resolution and timespans [7][8][9].…”

Precision CMB Measurements from Long Duration Stratospheric Balloons: Towards B-modes and Inflation

“…From the point of view of atmospheric opacity and stability, Antarctica is arguably the best site in the world to perform observations at millimeter and far-infrared wavelengths with terrestrial telescopes (Burton et al 1994, Storey et al 1998, Battistelli et al 2012); a review of South Pole based CMB experiments can be found elsewhere in these proceedings (Halverson 2012). In addition to the favorable conditions of the lower atmosphere, the stability of the stratospheric circumpolar winds during the Austral summer offers a unique capability for long duration balloon (LDB) flights (Gregory 2006).…”

On the emissivity of wire-grid polarizers for astronomical observations at mm-wavelengths

“…The NEP of the system under room-temperature background is around 10 −15 W/ √ Hz. This detector is the same used for the BRAIN experiment [11,12,13]. The detector is AC biased at 415Hz, while the chopper modulates the optical signal at 20 Hz.…”