Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The External Calibrator for Hydrogen Observatories   Multiple instruments are pursuing constraints on dark energy, observing
reionization and opening a window on the dark ages through the detection and
characterization of the 21cm hydrogen line across the redshift spectrum, from
nearby to z=25. These instruments, including CHIME in the sub-meter and HERA in
the meter bands, are wide-field arrays with multiple-degree beams, typically
operating in transit mode. Accurate knowledge of their primary beams is
critical for separation of bright foregrounds from the desired cosmological
signals, but difficult to achieve through astronomical observations alone.
Previous beam calibration work has focused on model verification and does not
address the need of 21cm experiments for routine beam mapping, to the horizon,
of the as-built array. We describe the design and methodology of a
drone-mounted calibrator, the External Calibrator for Hydrogen Observatories
(ECHO), that aims to address this need. We report on a first set of trials to
calibrate low-frequency dipoles and compare ECHO measurements to an established
beam-mapping system based on transmissions from the Orbcomm satellite
constellation. We create beam maps of two dipoles at a 9-degree resolution and
find sample noise ranging from 1 to 2%. Assuming this sample noise represents
the error in the measurement, the higher end of this range is roughly twice the
desired requirement. The overall performance of ECHO suggests that the desired
precision and angular coverage is achievable in practice with modest
improvements. We identify the main sources of systematic error and uncertainty
in our measurements and describe the steps needed to overcome them.

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The categories of this paper are: alg-geom
31
The categories of this paper are: ao-sci
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: comp-gas
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
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The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
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The categories of this paper are: q-fin