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Large-N seismometers networks, Distributed fibre optic sensing
Abstract:
We present an outstanding record of local, dense Large-N seismic and distributed acoustic sensor observations of a meteoroid from July 2, 2021 in Iceland. Our dataset includes high-quality observations from seven small aperture arrays of few hundred meters, an infrasound array, and a rotational station, all located within the distance range of 300 km. The high-frequency data show a variety of different phases associated with the source process along the atmospheric trajectory, including impulsive negative 1 first ground motions, a complex coda wave train about 2.5 s long thereafter, an azimuth-dependent stopping phase with reversed polarity between 1-25 s after the first arrival, which is resolved over only a few kilometers. The ground motion amplitude between the first and last arrivals is generally elevated. We associate the waveform in the 2.5 s coda with meteor-atmosphere interactions and nonlinear plasma processes that produce an oscillating shock-wave source pulse. Our data suggest a small azimuth-dependent deflection or dispersion of this source pulse, which may be related to the meteoroid’s deceleration in the atmosphere. We present a finite-length kinematic line-source pulse model that consistently explains the different phases inside and outside the Mach cone segment of our images, their wave amplitude variations, and a polarity change between the first phase and the terminating phase. The previously undiscovered rich directivity effects can also explain seemingly contradictory, time-dependent wave energy beam-directions at the various small aperture arrays and along the DAS cable. A combination of conventional locations and a Bayesian inversion of first and stopping phase arrivals led to a precise localization of the meteor trajectory.
