The sound from a propeller-driven aircraft is largely generated by the propeller itself. Its acoustic signature consists of a series of harmonics, the lowest of which, the fundamental, is typically in the region of 100 Hz, with the higher harmonics appearing at multiples of the fundamental. Experiments have recently been conducted off the coast of southern California, using several different types of single-engine, light aircraft, which show that the first 10 or so propeller harmonics are detectable not in the atmosphere, in the water column and also on sensors buried to a depth of about 1 m in the seabed. The Doppler-shifted comb of frequencies produced by an aircraft propeller is the basis of a recently developed technique for making point measurements of the low-frequency sound speed and attenuation in marine sediments