Acoustical measurements of bubble production by spilling breakers

The surface bubble spectral density of newly created bubbles has been measured under spilling breakers in a laboratory facility. This has been accomplished acoustically by passively identifying the radius, position, and time of creation of several hundred individual bubbles as their shock-excited pulsations radiate damped spherical waves of sound. The measured bubble spectrum ranges from radius 50 μm to 7.4 mm with a peak of 6 bubbles per square meter in a 1-μs-radius increment at radius 150 μs. The rate of bubble production has an exponential fall-off with time and 97% of the bubbles are produced in the first 500 ms after the breaker passes. The results supplement recent ocean data for low sea states.