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Infrared Imaging of Transient Luminous Events (1-1.5 µm) Over the Midwestern US and Comparison With Their Visible Wavelength Signatures

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Novel imaging of infrared sprite signatures were made as part of a coordinated campaign conducted from Yucca Ridge, Colorado during July and August, 2005. Four sensitive imaging systems were fielded by Utah State University to investigate the signatures of these transient luminous events (TLE's) over a broad spectral range, extending from near ultraviolet to infrared wavelengths. The USU instruments included:

  • An InGaAs imaging array operating at video rates to investigate infrared TLE signatures.
  • Two Intensified (Gen III) cameras, one filtered to observe the N2 first positive optical emissions (at 665 nm), and the second, unfiltered, to observe their visible emission structure.
  • An extended blue response intensified camera, fitted with a broad-band filter to observe the N2* first negative and N2 second positive emissions (band width, 350-475 nm).

All four cameras had similar fields of view (25°) and were co-aligned on single steerable mount. Our measurements were made in conjunction with high speed video and ELF/VLF observations providing detailed information on the TLE electrodynamics and their structures. Sprites have previously been imaged in the infrared from a high flying aircraft (C. Siefrieng, private communication). We discovered that sprites were easily imaged in the infrared spectral range, with over 40 events captured with the InGaAs camera from "spriting" storms over the Midwestern U.S.A.

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