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Estimation on Audibility of Large Cetaceans for Improvement of the Under Water Speaker

Yamada H., Kagami L., Yonehara Y., Matsunaga H., Kato H., Terada M., Takahashi R., Okanoya K., Kawamoto T.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

2012

Vol. 6, no. 4

589--593

In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker (UWS) has been installed on the HF. Because of its potential in utility, we tried to improve the UWS to minimize the risk of the collisions. Under our project, we examined three subprojects; 1) Analyzing the characteristics of the HF underwater noise; 2) Assessing audibility of major large cetaceans by measuring their vocalizations and 3) An anatomical prediction of the audible range by examining the cochlear basal membrane. Through the analyses, it was identified that the noise produced by the HF was a broad-band noise with approximately 150dB re 1μPa-m.That noise level was lower than those of larger boats suggesting difficulties for cetaceans in sensing approach of the vessels. In addition, analysis of their vocalizations and anatomical obervation indicated that dominant frequency of their audible range was lower than signals produced by the existing UWS.

Design and evaluation of IP multipath transmission with feedback

Kawamoto T., Goto K.

Systems Science

2009

Vol. 35, no 2

73-79

In this research, a simple multipath IP datagram transmission scheme is proposed and implemented as a user space router program. Delay and congestion vary along with time on each path and their estimation is difficult. In the proposed system, Multipath Tunneling Router (called MTR), traffic and delay of each path are periodically reported to the sender. An IP datagram is encapsulated in a UDP datagram and randomly transmitted to one of the paths according to the weight calculated with the feedback information from the receiving node. The path weight is based on the estimation of delay increase, which is measured as mean delay minus long term minimum delay of each path. The system is implemented as a user space tunneling router program on Linux and the performance is evaluated with a network emulator we have developed in a previous research. The program is rather small and consists of 1252 lines of codes in C++. The system is shown to be practical for two paths of different capacity and delay. Currently maximum throughput of the router implementation is about 65 Mbps with a single core CPU. It can be better with faster CPU.