Timing Calibration and Windowing Technique Comparison for Lightning
Since their introduction 22 years ago, lightning mapping arrays (LMA)
have played a central role in the investigation of lightning physics.
Even in recent years with the proliferation of digital interferometers
and the introduction of the LOw Frequency ARray (LOFAR) radio telescope,
LMAs still play an important role in lightning science. LMA networks use
a simple windowing technique that records the highest pulse in either 80
$\mu$s or 10 $\mu$s fixed windows in
order to apply a time-of-arrival location technique. In this work we
develop an LMA-emulator that uses lightning data recorded by LOFAR to
simulate an LMA, and we use it to test three new styles of pulse
windowing. We show that they produce very similar results as the more
traditional LMA windowing, implying that LMA lightning mapping results
are relatively independent of windowing technique. In addition, each LMA
station has its own GPS-conditioned clock. While the timing accuracy of
GPS receivers has improved significantly over the years, they still
significantly limit the timing measurements of the LMA. Recently, new
time-of-arrival techniques have been introduced that can be used to
self-calibrate systematic offsets between different receiving stations.
Applying this calibration technique to a set of data with 32 ns
uncertainty, observed by the Colorado LMA, improves the timing
uncertainty to 19 ns.