Underwater electromagnetics and its application to unmanned underwater platforms

Electromagnetic wave (EMW) has improved human life and is then essential technology for mankind, but it is basically useless in the sea. Although acoustic wave is the most effective means for underwater applications, it has disadvantages of long propagation delay and narrow bandwidth. Meanwhile, evolution of electronics and information technology improves ocean platforms such as buoys, landers, unmanned surface vehicles, and unmanned underwater vehicles as well as sensors. The upgrading of ocean platforms leads us to improve efficiency and reduce the cost of ocean research. To achieve practical unmanned platforms, we should build a seamless land-to-underwater wireless network for monitoring all platforms. Since 2002, we have restudied underwater EMW propagation and its applications for surface-to-sea communication, sea-to-sea communication, and underwater telemetry. The work includes the basic study of medium frequency (MF) to high frequency (HF) wave underwater propagation, the basic study of deep-sea optics, and the application study of underwater laser. Some test results show that there might be a low damping mode of HF wave propagation in the sea. It was determined that a few watt class blue-green laser propagates underwater up to hundreds meters. A laser ranging system was prototyped and carried sea trials. In the conference, we would like to report on progress of the studies including some test results and show examples of their application to underwater platforms in the future.