Comparison of the RF Frequency Spectra of HEMP and Lightning
Technical rept. 22 Sep 1987-10 Jul 1990
FLORIDA UNIV GAINESVILLE DEPT OF ELECTRICAL ENGINEERING
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Cloud pulses are much more common than these earlier studies indicate. Our spectra of the largest overhead cloud pulses are nearly parallel to but significantly below the HEMP spectrum from 1MHz to 50 MHz, while obtained from lighting tens of kilometer offshore over salt water show faster relative decay with increasing frequency, are significantly below ours between 10 and 50MHz, and are about equal to ours between 3 and 10 MHz. The shortest rise time to initial peak value of overhead lighting pulses are of the order of 0.3 micro sec. A broader bandwidth system than that used would allow measurement of the rapid field variation occurring throughout the cloud pulses associated with frequencies above abut 50 MHz but would observe essentially the same risetime to initial peak. That is, the higher frequency content of the cloud pulses is contained in the rapid field variation throughout the overall waveforms and not in the initial rise to peak value.
- Nuclear Weapons
- Electromagnetic Pulses