When an explosion or airgun is triggered in water, the resulting gas bubble oscillates with decreasing energy with each oscillation generating a pressure pulse, known as the ‘bubble pulse’. Unwanted bubble pulses can be prevented by setting off the source sufficiently close to the surface to allow the bubble to vent before it collapses, a method which, although spectacular, is inefficient. Where an array of tuned airguns is fired at depth, the individual airgun bubble pulses destructively interfere to provide the desired source signature. A knowledge of the bubble pulse period, T, is thus required for each source and this can be calculated using the Rayleigh-Willis formula such that: T = (0.0452Q1/3)/((D/0.3048) + 33)5/6, where Q is the source energy in joules and D is the water depth in metres to the bubble centre.
Subjects: Earth Sciences and Geography.