Abstract
In this study, an aspherical lens with the aperture diameter of 1.0 m was designed for utilization in an actual ocean experiment of ambient noise imaging (ANI). It was expected that this ANI system would realize directional resolution, which is a beam width of 1° at the center frequency of 120 kHz. We analyzed the sound pressure distribution focused by the designed lens using the 3D finite difference time domain method. The frequency dependence of a -3 dB area was then compared between 120 kHz and the higher or lower frequency. The analysis results suggested that the designed lens has fine directional resolution over the center frequency of 120 kHz. We had measured the directivity of the designed lens in an actual ocean experiment in Uchiura Bay in November of 2010. It was verified that the ANI system with this lens realizes a beam width of 1° at 120 kHz.