High-Precision Scanning Water Vapor Radiometers for Cosmic Microwave Background Site Characterization and Comparison

TL;DR

This study uses high-precision water vapor radiometers to compare atmospheric water vapor fluctuations at the South Pole and Summit Station, aiding the selection of optimal sites for future CMB polarization observations.

Contribution

It introduces a coordinated campaign deploying identical WVRs at two key sites to systematically characterize atmospheric water vapor effects relevant for CMB measurements.

Findings

Data collection at both sites began in 2016.

Ongoing analysis aims to produce comparable atmospheric water vapor statistics.

Results will inform site selection for future CMB experiments.

Abstract

The compelling science case for the observation of B-mode polarization in the cosmic microwave background (CMB) is driving the CMB community to expand the observed sky fraction, either by extending survey sizes or by deploying receivers to potential new northern sites. For ground-based CMB instruments, poorly-mixed atmospheric water vapor constitutes the primary source of short-term sky noise. This results in short-timescale brightness fluctuations, which must be rejected by some form of modulation. To maximize the sensitivity of ground-based CMB observations, it is useful to understand the effects of atmospheric water vapor over timescales and angular scales relevant for CMB polarization measurements. To this end, we have undertaken a campaign to perform a coordinated characterization of current and potential future observing sites using scanning 183 GHz water vapor radiometers (WVRs). So far, we have deployed two identical WVR units; one at the South Pole, Antarctica, and the other at Summit Station, Greenland. The former site has a long heritage of ground-based CMB observations and is the current location of the Bicep/Keck Array telescopes as well as the South Pole Telescope. The latter site, though less well characterized, is under consideration as a northern-hemisphere location for future CMB receivers. Data collection from this campaign began in January 2016 at South Pole and July 2016 at Summit Station. Data analysis is ongoing to reduce the data to a single spatial and temporal statistic that can be used for one-to-one site comparison.