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