Recent advancement in electronics technology is helping accelerate the development of new generation of underwater acoustic equipment. The transducer, a sensor of the underwater acoustic equipment, generally has directivity in its beam pattern. Many papers on the improvement of the directivity have so far been presented. However, most of the papers have focused the suppression of the level of sidelobe, and the improvement of the mainlobe has not been presented much. We have made their effort in the improvement of the mainlobe and have succeed in developing “quasi-ideal beam transducer”. This paper describes the theory of its beam forming and the method of its optimum design. Further, the practical design method and the measurement result of the directivity of the quasi-ideal beam transducer are described.
In monitoring of water mass structure in mid-deep water using multipath sound propagation, high accuracy measurement of the travel time of rays which propagate reflecting at surface and bottom is required. M-sequence signal with correlation technique, which is one of the pseudorandom sequence, is useful to obtain signal-to-noise enhancement and high temporal resolution. In this paper, we examine travel time estimation error and the stability of multipath propagation using M-sequence signal from sound transmission experiment data at Sagami Bay. Using the carrier frequency of 5 kHz, multipath arrivals up to the range of 25 km are successfully detected and identifiable. Travel time estimation results are stable and high accuracy measurement is achieved. It is considered that from bottom and/or surface reflected rays measurement of the perturbation of travel time corresponding to the ocean fluctuations can be accomplished.