Session: 05-04-01 CCUS and Underwater Development/ Utilization I

Submission Number: 180298

Verification of a Composite Navigation System for Underwater Vehicles Using Underwater Laser Doppler Velocity 

As is well known, the mainstream method for measuring the velocity of a moving object in seawater is the acoustic Doppler velocity measurement system, known as the Doppler Velocity Log (DVL).
The DVL emits directional acoustic waves in multiple directions, receives the waves reflected from the seabed or water currents, and detects the Doppler shift to measure the relative velocity between the sound source and the reflecting object. Thus, when a DVL is mounted on an underwater vehicle, it can measure the vehicle’s relative velocity to the surrounding water (water speed) or to the seabed (ground speed) when operating close to the seabed.

Underwater vehicles are also generally equipped with various types of sonar for seabed surveys, as well as acoustic devices for positioning and communication with a support ship. In addition, they include other acoustic navigation sensors such as an altimeter for measuring altitude from the seabed and an obstacle-avoidance sonar for detecting obstacles ahead. Consequently, many acoustic devices are installed in a limited space inside and outside the vehicle, and acoustic interference among their transmitted and received signals must be carefully managed—although complete elimination of such interference is very difficult. Furthermore, underwater vehicles are equipped with multiple rudders and thrusters as propulsion devices, which act as sources of acoustic noise for these acoustic instruments. Managing and isolating these acoustic devices and noise sources effectively is also very challenging.

Therefore, we are currently developing a new optical DVL technology that detects the Doppler shift of underwater laser light, in contrast to conventional acoustic DVLs. By applying optical principles to the velocity detection of underwater vehicles, we aim to achieve a silent and efficient velocity measurement system that is completely isolated from acoustic interference.

This paper describes an underwater laser Doppler velocimeter currently under development and presents results from deep-water field tests in which its performance was evaluated after being installed on an underwater vehicle. Furthermore, to demonstrate the practicality of this laser-Doppler velocity measurement, we describe a laser-Doppler composite navigation system that integrates the test results into the inertial navigation system (INS) of an underwater vehicle. Both the laser-Doppler composite navigation and pure inertial navigation were processed, and their position detection accuracies were compared, demonstrating the improvement in navigation performance achieved by the laser-Doppler composite system.

Presenting Author: Shojiro Ishibashi JAMSTEC (Japan Agency for Marine-Earth and Science Technology)

Presenting Author Biography: He obtained his doctorate (Ph.D) in 2003 from TUMM and then joined the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). He is a senior researcher. He has participated in the development of nine underwater vehicles, and was responsible for the development of CPU control systems, navigation systems, and motion control algorithms. In 2010, he began to research the underwater laser technologies for underwater use, and has been responsible for the development of several underwater laser systems including underwater laser scanners, an underwater laser communication and an underwater Doppler velocimeter, so far.

Authors:

Shojiro Ishibashi JAMSTEC (Japan Agency for Marine-Earth and Science Technology)