Quadrangles show the deduced source locations of the first elves luminosity in each photometer.
Constrained lower altitudes are also shown for some photometers. The time-resolved optical features of elves as measured in the Fly's Eye not only discriminate elves from other flashes, but also provide quantitative information regarding the location of each elve with respect to its causative CG lightning stroke. The onset of an optical flash in a photometer which is colocated with the VLF receiver is due to a VLF pulse propagating to an ionospheric point, and the resulting optical wavelengths propagating from that point to the photometer, both at the speed of light. Because the source of the photon production is constrained to be along the line of sight of the observer, the time difference between arrival of the sferic and an optical pulse in a photometer constrains the optical source location. The onset delays in each photometer for all the events ranged from 97 s to 620 s, where the longer times correspond to parts of the elves located behind the source lightning or far to the side of it.