Abstract-High-altitude electromagnetic pulse (HEMP) radiated from both primary and secondary currents, which are induced by a nuclear explosion, is computed by using the Jefimenko's equation. The effects of geomagnetic field is considered in computing the primary current, and the rough sea surface is considered in computing the reflected electric field in the frequency domain. The waveforms of HEMP near sea surface and a few km above it are simulated. The impulse and pulse characteristics are discussed, as well as the variation of peak field magnitude when the observation point is moved away from beneath the burst point.

Abstract-Transient field of a high-altitude electromagnetic pulse (HEMP) induced near ground is simulated, of which the ground reflection can not be neglected. The Jefimenko's equation is applied to compute the incident electric field near the ground, attributed to both the primary and the secondary currents in the source region. The field-dependent air conductivity in the source region is obtained by solving three nonlinear governing equations iteratively, and the reflected field is computed in the frequency domain.