Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by William Howard Hanot. / M.S.

New underwater passive sonar techniques are developed for enhancing target localization capabilities in shallow ocean environments. The ocean surface and the seabed act as acoustic mirrors that reflect sound created by boats or subsurface vehicles, which gives rise to echoes that can be heard by hydrophone receivers (underwater microphones). The goal of this work is to leverage this "multipath" phenomenon in new ways to determine the origin of the sound, and thus the location of the target. However, this is difficult for propeller driven vehicles because the noise they produce is both random and continuous in time, which complicates its measurement and analysis. Further, autonomous underwater vehicles (AUVs) pose additional challenges because very little is known about the sound they generate, and its similarity to that of boats. Existing methods for localizing propeller noise using multiple hydrophones have approached the problem either purely theoretically, or empirically such as by analyzing the interference patterns between multipath arrivals at different frequencies, however little has been published on building localization techniques that directly measure and utilize the time delays between multipath arrivals while simultaneously accounting for relevant environmental parameters. This research develops such techniques through a combination of array beamforming and advanced ray-based modeling that account for variations in bathymetry (seabed topography) as well as variations of the sound speed of the water. The basis for these advances come from several at-sea experiments in which different configurations of passive sonar systems recorded sounds emitted by different types of targets, including small boats and an autonomous underwater vehicle. Ultimately, these contributions may reduce the complexity and cost of passive systems that need to be deployed close to shore, such as for harbor security applications. Further, they also create new possibilities for applying passive sonar in remote ocean regions for tasks such as detecting illegal fishing activity. This dissertation makes three key contributions: 1. Analysis of the aspect-dependent acoustic radiation patterns of an underway autonomous underwater vehicle (AUV) through full-field wave modeling. 2. A two-hydrophone cross-correlation technique that leverages multipath as well as bathymetric variations to estimate the range and bearing of a small boat, supported by a mathematically rigorous performance analysis. 3. A multi-target localization technique based on directly measuring multipath from multiple small surface vessels using a small hydrophone array mounted to the nose of an AUV, which operates by cross-correlating two elevation beams on a single bearing.

The PSUBOT (pronounced pea-es-you-bought) is an autonomous wheelchair robot for persons with certain disabilities. Its use of voice recognition and autonomous navigation enable it to carry out high level commands with little or no user assistance. We first describe the goals, constraints, and capabilities of the overall system including path planning and obstacle avoidance. We then focus on localization-the ability of the robot to locate itself in space. Odometry, a compass, and an algorithm which matches points to lines are each employed to accomplish this task. The matching algorithm (which matches "points" to "lines") is the main contribution to this work. The .. points" are acquired from a rotating sonar device, and the "lines" are extracted from a user-entered line-segment model of the building. The algorithm assumes that only small corrections are necessary to correct for odometry errors which inherently accumulate, and makes a correction by shifting and rotating the sonar image so that the data points are as close as possible to the lines. A modification of the basic algorithm to accommodate parallel lines was developed as well as an improvement to the basic noise removal algorithm. We found that the matching algorithm was able to determine the location of the robot to within one foot even when required to correct for as many as five feet of simulated odometry error. Finally, the algorithm's complexity was found to be well within the processing power of currently available hardware.

Jos頍anuel Fonseca de Moura. / Prepared under Contract no. DAAB07-75-C-1346, Joint Services Electronics Program. Originally presented as the author's thesis, (Sc.D.), M.I.T. Dept. of Electrical Engineering and Computer Science, 1975. / Bibliography: p.197-199.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 188-193.

Sidescan Sonar has been the most popular probe for sea floor detecting in the underwater engineering. It is not only use to map the topography of the sea floor but also apply to the underwater search and rescue. Sidescan Sonar relies on commercial software, e.g. SonarPro, to record the raw data and draw images of the sea floor. However, SonarPro only presents the data to display segmental images, but it can not illustrate all images of the sea floor in one drawing. Researchers need to use the other software, called WizMap, to mosaic all Sidescan images in one drawing. WizMap is powerful for analyzing Sidescan data, but it is costly and has never been published its technology of Sidescan mosaic images. Thus we can not understand how Wizmap analysis raw data and make a mosaic drawing. Moreover, we could only accept the results it made, even the mosaic drawing is not correct. In this study, we implement a new analysis software package to facilitate reading raw data and drawing mosaic images of Sidescan Sonar. Sidescan Sonar provides basic function to record all digital raw data including GPS position, heading, roll, pitch, etc. We transfer the ship and Sidescan location from GPS to TM2 coordinate and illustrate the two side images along Sidescan trace in the same drawing. We will review the drawing and check all characteristics of these images and then adjust the heading offset and location offset to fit a better mosaic drawing. Finally, we combine all images into one mosaic drawing and compare two drawings between WizMap mosaic image and our mosaic drawing for confirming all results.

Bubbles are often present in the natural ocean. Bubbly liquid will have the significant influence the sound propagation, and creates a significant disturbance to under water target's detection. Therefore, it is an important research subject of bubble influence to the sound wave propagation. This study used the sonar training system which developed by British's iTP corporation, through suitable additional design discuss the attenuation of sound propagating through a bubble screen. At first this study collects and infers the formula by the literature review. Secondly, the experimental design of measuring the attenuation of sound wave. The experiment process by using two parallel iron boards to carry on the measurement of gas-volume fraction. Then correlate with the sound pressure from the measurement of hydrophone. After curve fitting, we can clearly know the each other correlation. Finally taking the result compare with the attenuation coefficient formula. The experimental consists of two parts. The first part is to measure the gas-volume fraction of the bubbly liquid contained in the screen; while the second part is to measure the sound attenuation of the bubble screen. The result display that the bubble screen can attenuate about 8 dB per centimeter as the gas-volume fraction stay at 1 percent. At high gas-volume fraction the coefficient of attenuation has increased, and is different from theoretical value. This is because the bubble's correlation has not been considered. In addition, the low frequency sound wave is close to theoretical value, but the high frequency sound wave has big different to theoretical value. Because the high frequency sound wave's wavelength is too small to satisfy the condition. At experiment I suggest to use more appropriate transducers and precise bubble's tube. Thus the experimental result will be better.

The purpose of this study was to integrate the principles of marine geotechnical engineering, underwater acoustic and optical observation techniques into studying the distribution of seafloor sediments and engineering stability of artificial reefs off Yong-an Harbor, Kaohsiung County, south-western coast of Taiwan. The artificial reefs were deployed to the testing site in November 9th, 1996. The goal of this study was intended to describe the engineering status of this reef site and to investigate whether these reefs were moved and buried or not; as well as, to predict whether additional reefs should be deployed to this site in the future. Long-term monitoring of underwater targets was conducted by using of side-scan sonar system, echo sounder, sub-bottom profiler, and underwater video camera. The utility of side-scan sonar system was to depict the topography and terrain features of the seabed. The other equipments were used to complement and cross correlate the results of side-scan sonar observations. In this study, wave forces against reef were estimated by Morison¡¦s equation(ex. Huang, 1995), scouring depth was calculated by Silvester¡¦s experience equation (Silvester, 1974), and the settlement of reefs by theoretical consolidation equation(ex. Das, 1990). The topography of Yung-an reef site is generally gentle and monotonous. The major texture of surficial sediments in this site was sandy silt, and some gravel was distributed at the southern part of the site. In terms of the stability on the artificial reefs project, Typhoon was the main factor which causes the reef to slide or roll. Verified by theoretical analysis and monitoring, the study area of the original stacked reefs has tumbled during the research period, while the remaining non-stacked reef shows insignificant displacement and quantity of the settlement found no cases being buried. To sum up, Yong-an artificial reef district in Kaohsiung county, respectively as A, B, C; the stacked reef under normal condition has found no significant reef being buried and moving traces and artificial reefs can fully elaborate by the gathers of the fish. According to the viewpoint of this project , "Direct contact with the reef and the body of the sea-bed " both the forces of the waves and ocean currents when a typhoon strikes is not easy for the reefs to glide. The "stacked reef" which causes the reef to slide or roll when typhoon occurs was caused by both the forces of the waves and ocean currents. "Direct contact with the reef and the body of the sea-bed " in the case of wave period of 10 sec, analysis shows that the wave height must be greater than 5.8 m in order to make the reef slide. "Stacked reef" in the case of wave period of 10 sec, analysis shows that the wave height must be greater than 4.5 m in order to make the reef roll.

Search for drowned human body by divers is a highly technical dependent, difficult and dangerous work. How to improve this kind of underwater rescue work, under the considerations of the safety of divers and the effectiveness in detection of the target within a limited period of time, is a major subject for fire fighters. For the time being, a normal search and rescue procedure basically includes visual observation of the bank area and surficial water area. In addition, divers are sometimes sent out to complement the search procedure by either visual observation or tactile. A much more efficient way to conduct this kind of recovery activity is to incorporate the state of art of the underwater acoustics technique, such as scanning sonar, into the operation procedures. This investigation was focused on the application of scanning sonar and image analysis techniques as well as seafloor object identification skills for the detection of drowned human body. In addition, safety of divers under water and their activities could be improved and monitored. Remotely operated vehicle (ROV) and towed operated vehicle (TOV) should be incorporated into the normal search procedure for the purpose of improving target identification in the future. Under this circumstance, both target searching rate and divers¡¦ safety could be effectively improved or guaranteed. The proposed procedure which incorporated both acoustical (i.e., scanning sonar) and optical (i.e., ROV or TOV) apparatus are expected to simplify and improve the underwater target search and identification activities and will allow fire fighters a more professional and safety way in conducting drowned human body recovery activities.

Abstract Sciaenids are a kind of economic oceanic fish with the most dynamic vocal activity. It is important to find out what type of sound a soniferous fish can make. Therefore, I used this acoustic character as a tool to study the distribution of sciaenids in order to manage their fisheries. In the previous researches, scientist found that there were eight types of sounds (A~H type) appearing on the coastal areas of Yunlin, and the frequency range of the H-type sound could reach to 8000Hz. This sound was suspected to be made by Otolithes ruber. Connaughton (1994) and Sprague (2000) mentioned that the differences of length, weight, and tension of the sonic muscle and the amount of protein and glycogen affect the types of sounds emitted. To reveal the producer of high-frequency sound, this research analyzed and compared the length, width, thickness and somatic of sonic muscle and the amount of protein and glycogen in seven sciaenid species occuring on the west coast of Taiwan (Johnius tingi, Johnius sina, Johnius amblycephalus, Johnius amblycephalus, Pennahia argentata, Chrysochir aureus, and Otolithes ruber), then to find if the differences of physic parameter and energy supplication are the major factors making O. ruber produce high frequency of sound. In this research, I found that the length of O. ruber¡¦s sonic muscle was shorter than that other of sciaenids. However the weight of sonic muscle did not significantly differ although it was still the lightest one (2.33¡Ó1.00g). The amount of protein (20.37¡Ó0.67¢M) and glycogen (0.33¡Ó0.11¢M) in O. ruber was higher than that of other species and the cross section of sonic muscle fiber was smaller. These characteristics are suitable for O. ruber to make a high-frequency sound. Because of the sound is believed to be made by rubber, so passive sonar was applied to investigate the distribution of this sound type on the estuaries along the west coast of Taiwan (Tam-Shui River, Tou-Chien River, Ta-Chia River, Cho-sui River, Zeng-Wen River, and Kao-Ping River) to represent distribution of O. ruber and its seasonal change of vocal activity. Acoustic activity reached it peak in spring then decreased through summer, autumn, and winter. More sounds were found in the estuaries south of the Cho-sui River (including Cho-sui, Zeng-Wen, and Kao-Ping River) than those north of this river (including Ta-Chia, Tou-Chien, and Tam-Shui River).