How is thunder measured?
Bill Sellers,  Chicago  Dear Bill,  To answer your last question first: The noise level of thunder does not have to be above a certain value for thunder to be classified as thunder. The only requirement is that thunder be loud enough to be heard. The sound intensity of thunder diminishes as one moves progressively farther from the lightning that produced the thunder until, finally, the sound of the thunder is too faint to be heard. Other then microphones used in meteorological experiments involving lightning and thunder, there are no microphones in official locations to record the intensity of thunder.