Abstract
We present a feasibility study for a high frame rate, short baseline auroral tomographic imaging system useful for estimating parametric variations in the precipitating electron number flux spectrum of dynamic auroral events. Of particular interest are auroral substorms, characterized by spatial variations of order 100 m and temporal variations of order 10 ms. These scales are thought to be produced by dispersive Alfv\'en waves in the near-Earth magnetosphere. The auroral tomography system characterized in this paper reconstructs the auroral volume emission rate to estimate the characteristic energy and location in the direction perpendicular to the geomagnetic field of peak electron precipitation flux using a distributed network of precisely synchronized ground-based cameras. As the observing baseline decreases, the tomographic inverse problem becomes highly ill-conditioned; as the sampling rate increases, the signal-to-noise ratio degrades and synchronization requirements become increasingly critical. Our approach to these challenges uses a physics-based auroral model to regularize the poorly-observed vertical dimension. Specifically, the vertical dimension is expanded in a low-dimensional basis consisting of eigenprofiles computed over the range of expected energies in the precipitating electron flux, while the horizontal dimension retains a standard orthogonal pixel basis. Simulation results show typical characteristic energy estimation error less than 30% for a 3 km baseline achievable within the confines of the Poker Flat Research Range, using GPS-synchronized Electron Multiplying CCD cameras with broad-band BG3 optical filters that pass prompt auroral emissions.
Highlights
Studies of the aurora using two or more cameras with overlapping fields of view (FOV) have been carried out for over a century [1], with more recent work focusing on the formal application of tomographic techniques [2]–[5]
We demonstrate that Electron Multiplying CCD (EMCCD) camera technology coupled with a physics-based regularization scheme is capable of resolving electron differential number flux dynamics of order 100 m and 10 ms
We have shown results from a regularization scheme using the physics encapsulated in TRANSCAR modeled eigenprofiles in a two camera simulation, with testing extended to three cameras for future 3-D work
Summary
Studies of the aurora using two or more cameras with overlapping fields of view (FOV) have been carried out for over a century [1], with more recent work focusing on the formal application of tomographic techniques [2]–[5]. Auroral tomography provides a means of accessing time-dependent information about remote auroral acceleration processes In this technique, common volume measurements of the aurora from multiple ground-based imagers are used to reconstruct the wavelength-dependent ionospheric volume emission rate. The short distance between cameras was motivated by the desire to get the highest feasible resolution in the direction perpendicular to the geomagnetic field B⊥ [8] These data inversion techniques provide the first realizable method of obtaining a persistent two-dimensional (energy, B⊥) high resolution morphology estimate of the rapidly evolving electron precipitation above the ionosphere at the smallest ground-observable scales.
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