Observations

On June 22nd, 1997, the NMT interferometer was armed in an RF-threshold mode at 00:30 UT in support of a high-elevation ($77^{\circ}$) Optical Transient Detector (OTD) overpass at 00:35 UT. The system continued to acquire RF-thresholded data after the overpass until about 01:48 UT, when the system was transitioned to a FA-threshold mode. The FA-threshold mode was activated at 01:50:20 UT and was not deactivated until an hour later at 02:50:25 UT, when the system was transitioned to a sferic-recording mode.

Video recording from a Xybion low light level camera began at 01:12:30 UT, a half hour before the first sprite was observed. Video was recorded continuously until 03:49 UT, which was more than an hour after the last sprite event had been observed. The Xybion camera was equipped with the widest angle lens available, a 12.5 mm lens, in order to cover the large angular region of sky above the close storm system. The field of view of the 12.5 mm lens was determined by a stellar fit (see Appendix B.3.1) to be $55.7^{\circ}{\times}45.6^{\circ}$. The camera was pitched up to an elevation angle of $\simeq43^{\circ}$ above the horizon, which was high enough that sprites would appear near the center of the video image while the bright and potentially image-saturating ``close'' discharges would be below the field of view. In spite of this precaution, some of the discharges were still saturating the camera due to scattered light reflecting into the lens from the lens rim. To eliminate this scattered light, black electrical tape was placed on the lens rim at about 01:26 UT.