| A geoacoustic inversion technique using sound generated by propeller-driven light-aircraft has been developed for applications in underwater acoustics. In its simplest form, this method uses a single sensor in the ocean and the Doppler-shifted, narrow-band component of aircraft noise to determine the acoustic properties of marine sediments. In conjunction with this work, a wavenumber integration model and a normal-mode model have been developed for an airborne, constant speed, harmonic point-source in horizontal motion over a range-independent ocean, and are capable of computing the pressure field at any receiver location as a function of time. Acoustic measurements of a variety of aircraft have been made in both static and in-flight conditions and ocean experiments have been conducted using acoustic sensors in the air, water and buried in the sediment. Using the sensor in the air, estimates can be obtained of the aircraft speed, altitude, fundamental frequency and time at the closest point of approach. From a sensor in the water column or the sediment, estimates can be obtained of the sediment sound speed and attenuation. Data have been collected for an experimental site off the coast of La Jolla, California. The sound speed estimate of 1652.3 m/s and attenuation estimate of 0.40 dB/lambda using the 79 Hz harmonic of the engine are within the range of expected values for the fine to very-fine quartz sand sediment found in this area. |
