m-thesis-documentation/documents/thesis/chapters/conclusion.tex

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\begin{document}
\chapter{Conclusion}
\label{sec:conclusion}

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Using radio antennas to detect \glspl{UHECR} has received much attention recently.
The \acrlong{Auger} is currently being upgraded to \gls{AugerPrime} incorporating radio detectors with scintillators and water-cherenkov detectors.
Other experiments, such as \gls{GRAND}, plan\Todo{word} to fully rely on radio detection only.
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% Timing not enough
Time information in such large observatories is typically distributed using \glspl{GNSS}, reaching up to $10\ns$ accuracy under very good conditions.
For analysis using radio interferometry to be competitive, this timing accuracy needs to be improved towards the $1\ns$ mark.
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% Beacon introduction %<<<
A viable method to obtain this timing accuracy is to incorporate a beacon transmitter into the array.
This (narrow-band) transmitter sends out a special signal that is picked up by the radio antennas in the array.
With relatively simple techniques, the timing accuracy can be improved to below $1\ns$.
Thus, at a relatively low cost, the (relative) timing of radio arrays can be improved to enable radio interferometry.
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% Passive Beacon %<<<
In some circumstances, an external transmitter can be used as a beacon.
For example, in \gls{Auger}, a public TV broadcaster emits its signal at $f = 62.75\MHz$.
With the source location and the frequency known, time delays can be calculated and this signal can be used to account for timing errors smaller than $T = 1/f \sim 16\ns$.
Unfortunately, with the \gls{GNSS} timing accuracy estimated in the same order of magnitude and the signal being periodic, the synchronisation of the antennas can be off by an integer amount of periods $T$.
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% Combined sine beacon + air shower %<<<
Recording an air shower, in addition to such a narrow-band beacon, might provide a method to determine the correct beacon period.
Radio interferometeric analysis of the air shower depends on the coherence of the received signals.
Any synchronicity problems in the radio antennas decrease the coherence and thus the power mapping used to derive properties of the air shower.
With a limited set of periods to test, this power can be maximised while simultaneously inferring the correct beacon period.
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The developed method to synchronise can be directly tested at \gls{Auger}, both with data from \gls{AERA} and the upcoming radio detectors from AugerPrime.
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