Operation WIGWAM was a test of a 30 kt nuclear depth charge conducted in deep water 500 miles southwest of San Diego on 14 May 1955. Its primary purpose was to determine the effectiveness of that device as an antisubmarine weapon. The acoustic pulse from the test, initially an intense shockwave, radiated throughout the North and South Pacific Oceans. Acoustic reflections from topographic features were recorded for several hours after the explosion by SOund Fixing And Ranging (SOFAR) hydrophones at Point Sur, California, and Kaneohe, Hawaii. Sheehy and Halley (1957) identified peaks of the recorded coda with reflections from specific topographic features at great distances (e.g., the Hawaiian Islands, French Polynesia, or Fiji). With modern data for seafloor topography and ocean sound speed, these coda were computed with surprising accuracy using simple geodesic rays reflected from islands and seamounts. The intensity variations of the coda are mostly determined by simple ray geometry, together with modest attenuation. Coda peaks are often obtained from rays arriving simultaneously from multiple, but disparate, topographic features.
Online Material: Figures of computed and measured coda and associated geodesic paths.