The Atacama Cosmology Telescope: Modeling Bulk Atmospheric Motion

Abstract

Fluctuating atmospheric emission is a dominant source of noise for ground-based millimeter-wave observations of the CMB temperature anisotropy at angular scales $\gtrsim 0.5^{\circ }$. We present a model of the atmosphere as a discrete set of emissive turbulent layers that move with respect to the observer with a horizontal wind velocity. After introducing a statistic derived from the time-lag dependent correlation function for detector pairs in an array, referred to as the pair-lag, we use this model to estimate the aggregate angular motion of the atmosphere derived from time-ordered data from the Atacama Cosmology Telescope (ACT). We find that estimates derived from ACT's CMB observations alone agree with those derived from satellite weather data that additionally include a height-dependent horizontal wind velocity and water vapor density. We also explore the dependence of the measured atmospheric noise spectrum on the relative angle between the wind velocity and the telescope scan direction. In particular, we find that varying the scan velocity changes the noise spectrum in a predictable way. Computing the pair-lag statistic opens up new avenues for understanding how atmospheric fluctuations impact measurements of the CMB anisotropy.

References in corpus (3)

• Parque Astronómico de Atacama: An ideal site for millimeter, submillimeter, and mid-infrared astronomy
• Twenty years of PWV measurements in the Chajnantor Area
• Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A First Detection of Atmospheric Circular Polarization at Q Band

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• The Atacama Cosmology Telescope: Measurement and Analysis of 1D Beams for DR4
• The Atacama Cosmology Telescope: DR6 Power Spectrum Foreground Model and Validation
• Measurement and Modeling of Polarized Atmosphere at the South Pole with SPT-3G
• The Simons Observatory: Beam characterization for the Small Aperture Telescopes
• The Atacama Cosmology Telescope: Quantifying Atmospheric Emission above Cerro Toco
• Simons Observatory Focal-Plane Module: Detector Re-biasing With Bias-step Measurements
• Energy Recovery System for Large Telescopes
• The Atacama Cosmology Telescope: Machine Learning Driven Tools for Detecting Millimeter Sources in Timestream Pre-processing