In order to examine the effects of air bubble in the ear canal for underwater hearing, detailed measurement of minimum audible field (MAF) in audio frequency (50Hz-8kHz) and comparison of loudness were carried out at two conditions as below, 1) the air bubble remains in the ear canal and 2) the ear canal is filled with water. As the result, in the high frequency region over about 300 Hz, it is highly sensitive to hearing in the case that the air bubble remained in the ear canal. In the low frequency region under 300 Hz, it becomes more sensitive in the case that the ear canal was filled with the water by removing the air bubble.
The reverse phenomenon of “hearing” at about 300 Hz is explained by difference between frequency characteristics of the occlusion effect (air conduction) and the effect in which the ear canal was filled with the water (bone conduction).

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Synthetic Aperture Sonar has a great advantage of high azimuth resolution compared with legacy side scan sonar. Calculating theoretical resolution of Synthetic Aperture Sonar, it needs approximations and limitations to express that as elementary mathematics. In this study, we discuss an influence on resolution by these mathematical approximations and limitations. We had made a trial Synthetic Aperture Sonar to study basic characters both of theory and experiment. As a result of our experiment at acoustic tank, it is turn out that resolutions on experiment, simulation and theory are same. And we discuss about conditions to achieve theoretical resolutions at sea area.

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