Fuyuki Katase

3D Acoustic imagery generation by interferometric analysis of long baseline using Interferometric Real Aperture Sonar.

We are developing a technique for the systematical exploration of submarine hydrothermal ore deposits. In the Izu-Ogasawara Arc area these deposits are usually characterized by the existence of tower-like vents 2~20m high by 2~5m wide. We are using a set of Interferometric Real Aperture Sonars (InRAS) to generate 3D acoustic images of the areas surrounding the vents. We not only improved the resolution thanks to a long interferometric baseline, but we also efficietnly unwrapped the phase in this zone of large elevation differences by applying a two-stage approach (Branch Cut and SSPU methods). These improvements allow us to map the seafloor bathymetry around the submarine hydrothermal deposits. Since April 2014 we are conducting in-situ observations of both known and potential zones of hydrothermal deposits. Moreover, in November 2015 we will gather validation data in an experimental pool.

Development of the parametric sub-bottom profiler for autonomous underwater vehicles — Prediction of the reflection level using sonar equation based on TBE and Biot-Stoll model

The exploration of buried deposits under the sea sediment requires high directivity and low attenuation beams. The parametric sub-bottom profiler (PSBP) meets these requirements; moreover, it is comparatively small and can be easily mounted on autonomous underwater vehicles (AUVs). For this reason, we are developing a new PSBP system for AUVs. In this study, the performance of the PSBP system is estimated by using a sonar equation based on the transformed beam equation (TBE) and the Biot-Stoll model to optimize the measurement system.

AUV IRSAS for submarine hydrothermal deposits exploration

Small AUV “IK-A” equipped with IRSAS was developed for submarine hydrothermal deposits exploration. Observed IRSAS data could acquire the back scatter image and bathymetry. One of the features of the seafloor hydrothermal deposits is the chimney and the mound-like terrain. Back scatter image can distinguish these terrain and other terrains. IRSAS has increased much measurable terrain by switching the pointing angle and real/synthetic aperture. On the other hand, perturbations of small IK-A, it was detected that affects the synthetic aperture processing. At the moment, there is a need to solve the problems of the following two points. Improving motion correction for synthetic aperture processing. Determination of the switching criteria of the narrow beam transmitter or wide beam transmitter.

Development and sea trial of the parametric sub-bottom profiler system for autonomous underwater vehicles-off Hatsushima Island-

The exploration of buried deposits under the sea sediment requires high directivity and low attenuation beams. The parametric sub-bottom profiler meets these requirements; moreover, it is comparatively small and can be easily mounted on autonomous underwater vehicles (AUVs). For this reason, we are developing a new PSBP system for AUVs. This paper presents the recent results of the PSBP system for AUV during the sea trial conducted under the “Zipangu of the Sea” Project as a sub-program of SIP (Strategic Innovation Promotion), managed by the Cabinet Office of the Japanese government.