A series of medium‐size explosions are monitored by a variety of ground sensors. A preliminary study of one typical explosion at 250 meters above the ocean surface has revealed many interesting results; from the acoustical signal the effects of the atmosphere on infrasonic waves generated as a pulse have been identified both as a function of frequency and as a function of distance. VLF and ELF electromagnetic signals have been observed by stations more than 100 kilometers from the explosion center. The signals are described fully, and the experimental objectives are summarized.