High-speed Camera System

A KODAK EktaPro High-Spec Motion Analyzer Model 1012 with a KODAK EktaPro Intensified Imager Model VSG was used to acquire the high speed video imagery of sprites. The pixel array size of the imager sensor was 239x192. The operational wavelength region was 440-700 nm at 50% sensitivity and 350-800 nm at 10% sensitivity. The system was capable of 1000 frames per second (fps) using the full sensor area and higher rates using correspondingly fewer horizontal scan lines. The frame start times were accurate to within 50 $\mu$s as determined by GPS timing (see Appendix B.4.2).

The high-speed camera's pixel sensor was scanned out in blocks of 16 rows each for a total of $192/16=12$ blocks (at 1000 fps). This scanning proceded downward from the top of the sensor's active area. Each block had integration start and end times that were delayed by $1~ms/12=83~{\mu}s$ from the block immediately above. The lowest block of the frame preceded the top block of the next frame by 83 ${\mu}$s. This timing information was utilized in analyzing the images, and into the velocity estimates.

The light integration period was configurable, but was always set to match the duration of the individual blocks within a frame. There was a short period during a block's read-out interval when light could not be integrated. The duration of the scan-out interval was ${\approx}$1 $\mu$s, which was too small to have a noticeable effect on the images.