  Applying the directionality of a Luneburg lens, a sound reception system for
ships is designed. A two-dimensional acoustic Luneburg lens which is made of
253 acrylic pipes of different radii which control the refractive index is
used. It has a large disk shape; a diameter of 180 cm and a height of 20 cm.
The 8 microphones were installed around the edges of the lens. The sound
reception ability of the lens was tested on the sea using the horn of a
university training ship as an emitter and the lens loaded on a small boat as a
receiver. Both are moving at 20 ~ 40 km/h at a distance of between 300 ~ 700 m.
The lens could focus to recognize the direction of the input sound in the
frequency range between 300 ~ 900 Hz.
