Improvements in a Lightning-Measuring Instrument

Some improvements have been made in the instrument described in "Instrument Records Magnetic Fields Generated by Lightning" (KSC-11769) NASA Tech Briefs, Vol. 19, No. 4 (April 1995), page 38. To conserve battery energy, the instrument was made to record the output of only one of three mutually orthogonal loop antennas and to operate in a "sleep" mode except when "awakened" by a lightning strike. Unfortunately, with this energy-conserving strategy, sometimes even a nearby lightning strike could fail to wake the system up on time to record the first strike. The improvements, directed toward overcoming this trigger deficiency, include (1) replacing the "sleep" mode with a mode in which the signals from all three antennas are sampled sequentially at a reduced rate and multiplexed onto one channel and (2) modifying the triggering scheme and the "awake" mode so that once a signal in at least one channel exceeds the trigger threshold, the signals from all three antennas are sampled at a high rate simultaneously on three digitizing channels for 100 µs. Signal samples acquired at the reduced rate for the past 100 µs at the moment of triggering are stored, along with the samples acquired at the full rate for the 100 µs following the moment of triggering.