Although acoustic impedance of air is much lower than that of water, and the reflected wave dominates the energy when an acoustic wave is incident from air to water, it is well known that sound from an airborne source is detectable beneath the ocean surface. Location of an airborne source is estimated from signals measured by a horizontal line array (HLA), based on the fact that a signal transmitted by an airborne source will reach an underwater hydrophone in different ways: via a direct refracted path, via one or more bottom and surface reflections, via the so-called lateral wave. As a result, when an HLA near the airborne source is used for beamforming, several peaks at different bearing angles will appear.

In practice, inverse problems such as geoacoutic inversions and source localizations have received much attention in underwater acoustics. The experiment research on the airborne source localization from underwater sound is rarely reported. So PENG Zhaohui, LI Zhenglin and WANG Guangxu of State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences carried out a series of studies and conducted an experiment for airborne source localization in the Yellow Sea.

By matching the experimental beamforming outputs with the predicted outputs for all source locations, the most likely location is the one which gives minimum difference. An HLA was laid on the sea bottom at the depth of 30m. A high-power loudspeaker was hung on a research ship floating near the HLA and sent out LFM pulses. The estimated location of the loudspeaker is in agreement well with the GPS measurements.