Modelling ground pickup for microwave telescopes

TL;DR

This paper develops an extended beam convolution algorithm to simulate ground pickup in microwave telescopes, aiding in experiment design and data analysis for CMB measurements.

Contribution

It introduces a novel extension to the beamconv algorithm that models simultaneous sky and ground pickup in time-ordered data simulations.

Findings

Successfully simulates ground pickup for ground-based and balloon experiments.

Uses satellite maps to create ground emission templates for balloon experiments.

Provides a tool to improve systematic control in CMB observations.

Abstract

Microwave telescopes require an ever-increasing control of experimental systematics in their quest to measure the Cosmic Microwave Background (CMB) to exquisite levels of precision. One important systematic for ground and balloon-borne experiments is ground pickup, where beam sidelobes detect the thermal emission of the much warmer ground while the main beam is scanning the sky. This generates scan-synchronous noise in experiment timestreams, which is difficult to filter out without also deleting some of the signal from the sky. Therefore, efficient modelling of pickup can help guide the design of experiments and of analysis pipelines. In this work, we present an extension to the beamconv algorithm that enables us to generate time-ordered data (TOD) from beam-convolved sky and ground maps simultaneously. We simulate ground pickup for both a ground-based experiment and a telescope attached to a stratospheric balloon. Ground templates for the balloon experiment are obtained by re-projecting satellite maps of the Earth's microwave emission.