Yasunobu Yagita

High Speed Acoustic Network And Noncontact Power Supplier For Seafloor Geodetic Observing Robot System

A new effective seafloor geodetic observing robot network system has been proposed and is under construction in Japan, which consists of several submarine stations where interplate earthquakes tend to occur. Each station with an autonomous underwater vehicle (AUV) dock is connected to a land facility with cables for power feeding and communications. Near the AUV dock, three or four seafloor reference stations will be expanded for geodetic observation. In this system high bit rate and low error rate are required when uploading mass observed geodetic data from the AUV to its dock without a cable connection. A prototype acoustic network system with 100 kilobit per second (kbps) high rate and point-to-point protocol (PPP) implementation has been developed using a phase shift keying (PSK) modulation. Noncontact power feeding system is another key technology which enables AUVs to conduct observation for a long time. In this paper an efficient noncontact high power feeding system with 400 watts and 86% inverting efficiency for AUVs will also be described.

Short Range High Speed PPP-based Underwater Acoustic Network System

A prototype underwater acoustic network system with 100 kilo bits per second (kbps) and point-to-point protocol (PPP) implementation was developed last year using a binary phase shift keying (BPSK) modulation for a new effective seafloor geodetic observing robot network system. At that time, a serial line was used for one-way data transmission because only one set of acoustic transmitter and receiver was available from our budget. In order to realize a transmission bit rate of above 500 kbps, now not only a new set of two-way acoustic communication hardware has been developed, but also the carrier frequency has been raised to 1-3 MHz from 500 kHz used in the old system. Presently we are trying to achieve above 500 kbps high bit rate.

New USB-based 3D digital echo sounder system for mapping and assessing fish and aquatic plants

A recently developed echo sounder with a global positioning system (GPS) receiver can display both the boat position and echo gram. However, this information is displayed in different views. In this paper, we present a new digital three-dimensional (3D) echo sounder system comprising a traditional analog echo sounder, GPS receiver, notebook personal computer (PC), and a low-cost, compact, self-developed universal serial bus (USB)-based analog-to-digital (A/D) converter board. Multiple echo views can simultaneously display various desired targets more clearly than the view in a traditional analog echo sounder. The newly developed analysis software can precisely extract the information related to bottom depth, plants, and fish schools from the echoes. By combining the acoustic and position data, the system can map both the fish and plant echoes on the 3D sea bed generated from the extracted bottom depth. This system has been proved to be useful in observing the 3D and wide-area distribution of both fishes and aquatic plants and in studying habitat parameters in aquatic ecosystems. A notebook PC equipped with the self-developed USB-based A/D converter board is capable of transforming any traditional analog echo sounder into a high-performance 3D digital echo sounder.

High Speed Acoustic Network with 2MHz Carrier Frequency for Seafloor Geodetic Observation Robot System

A new and effective seafloor geodetic observing robot network system, which consists of several submarine stations situated in regions susceptible to interplate earthquakes, has been proposed and is under construction in Japan. In this system high bit rate and low error rate are required when uploading mass observed geodetic data from AUV to its dock without cable connection. We proposed an acoustic network system aimed to realize a transmission bit rate of 500 kilobits per second (Kbps). As the first step, to verify the feasibility of the proposed system, a prototype acoustic network system with 100 kilo bit per second (kbps) high rate and pair to pair protocol (PPP) implementation was developed using Phase Shift Keying (PSK). At that time, a serial line was used for data transmission from the dock to AUV because only one set of acoustic transmitter and receiver was available from our budget. Now not only a new set of two way acoustic communication hardware has been developed, but also the carrier frequency has been raised to 2 MHz from 500 kHz used in the old system. Presently we are trying to achieve 500 kbps high bit rate communication.