This report proposes a new signal processing method in the Lofar-Gram used target signal detection in the passive sonar. Conventionally, we used FFT-method for frequency analysis in the Lofar-Gram. But it has some problems when a super-narrow band FFT analysis is utilized. So, we use an instantaneous covariance method that is an improved version of covariance method being one of the linear predictive method, and certified this method has better performance than conventional FFT-method.

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One of the most simple and effective ways for preventing the diving accidents is to transmit an underwater acoustic signal directly to divers. The use of an audio signals is very efficient since divers usually have no communication apparatus. Although it is well known that we have auditory sensation in the water, the appropriate expression of loudness are not well studied. In this paper, for the sake of appropriate assessment of underwater acoustical environment for the divers, the result of equal-loudness level of auditory sensation and minimum audible level in the water are summarized as an equal-loudness contours in the water. Then, after two additional experiments, we discussed the relation of contours between in air and in water.

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