Approved for public release; distribution is unlimited. / Acoustic propagation in the littoral regions of the world, even over short ranges, can be complex at high frequencies (>5 kHz), and applications such as underwater detection and communications suffer as a result. To this end, the Asian Seas International Acoustics Experiment (ASIAEX) was conducted with funding from the Office of Naval Research. One phase of this experiment took place from 29 May to 9 June 2001 and focused on short-range, shallow water acoustic propagation in the East China Sea. This thesis will be based on some of the measurements taken during the East China Sea experiment by a team from the Applied Physics Laboratory of the University of Washington. The environmental parameters and array geometry used in this and previous modeling work are as close as possible to the experiment. The objective of this thesis is to better understand the nature of turbulent perturbations and how they affect short-range acoustic propagation in a shallow water environment. This will include variations in total energy of the turbulence, variations in associated length scales, and variations in depth. In addition, the influence of other variable factors on signal coherence will also be examined. Most notably, variations in background sound-speed structure and source depth variability will be included. / Lieutenant Junior Grade, Turkish Navy

In the interest of enhancing the capabilities of autonomous underwater vehicles US Naval Operations, controlling vehicle position to follow depth contours presents exciting potential for navigation. Use of a contour tracking control algorithm in lieu of preprogrammed waypoint navigation offers distinct advantages within new challenges. The difficult nature of this problem lies in the non-trivial connection between the necessary corrective action and the feedback error used in traditional control methods. Stated simply, modern vehicle control algorithms separate horizontal and vertical plane navigation. The autonomous vehicle senses heading error and applies rudder to steer the vehicle to a desired heading. Simultaneously, the vehicle might sense altitude and apply stern plane angles to maintain a safe height above ground. This thesis research examines the new problem of sensing depth and altitude in the vertical plane while steering the vehicle horizontally to find a specified bathymetry contour. While more remains to understand, this research proves the existence of a solution and suggests similar approaches may facilitate tying vehicle navigation to other indirect sensors. This thesis presents two contour tracking control algorithms and examines the performance of each by simulating the response of the REMUS underwater vehicle to ideal and real-world bathymetry models.

CIVINS / This thesis presents a simulation of autonomous underwater vehicle navigation using a single transponder to create a virtual long baseline (VLBL). Similarly to LBL systems, ranges in a VLBL are calculated between the vehicle and the transponder, but the vehicle position is determined by advancing multiple ranges from a single transponder along the vehicles dead reckoning track. Vehicle position is then triangulated using these successive ranges in a manner analogous to a 'running fix' in surface ship navigation. Navigation data from bottom survey operations of an underwater vehicle called the Autonomous Benthic Explorer (ABE) were used in the simulation. The results of this simulation are presented along with a discussion of the benefits, limitations, and implications of its extension to real-time operations. A cost savings analysis was also conducted based both on the idea that a single surveyed beacon could be deployed for underwater navigation and on the further extension of this problem that the 'single beacon' used for navigation could be located on the ship itself. / Contract number: N62271-97-G-0026. / CIVINS / US Navy (USN) author.

Approved for public release; distribution is unlimited. / Current underwater acoustic communication systems operate in the frequency band of 1 - 10 kHz and utilize various forms of signal processing to improve data rates. In this work, the influence of the environment on long-range propagation of acoustic signals will be examined over the band of 1-5 kHz. The transmission loss (Th) as a function of range over the bandwidth will be one measure to determine the optimal operating character of the communications channel. Additionally, estimates of signal variance over the bandwidth as a function of range will be computed. The variance will be generated from source platform motion and interface roughness. Particular attention will be paid to the 2 - 4 kHz band of certain operating systems for long-range transmission / Lieutenant, United States Navy

Underwater acoustic networks provide an interface between UUVs and surface or land-based control systems. By exploiting range data measured incidental to communications on these networks it is possible to perform underwater positioning similar to that of the satellite-based GPS program. In this thesis, several algorithms for generating position fixes from these range data are implemented, tested, and evaluated with synthetic data. The algorithms are then applied to data obtained during operations at sea. / US Nany (USN) author.

Approved for public release; distribution is unlimited. / SeaWiFS data converted to optical properties of the ocean in the form of vertical and horizontal underwater visibility products are compared to in-water diver and optical instrument measurements during the Model Diver Visibility (MoDiV) experiment. Results were collected from 19 to 21 August in the Mississippi Bight region of the United States. The SeaWiFS satellite data was processed with the Automated Processing System (APS), developed by the Naval Research Laboratory (Code 7333). APS converted radiance values into specific parameters studied: the beam attenuation coefficient, the diffuse attenuation coefficient, vertical visibility and horizontal visibility. These values were compared to the AC-9instrument, a-Beta instrument, Secchi disk and the observed visibilities from the divers. The results indicated that the beam attenuation coefficient and the diffuse attenuation coefficient are underestimated as compared to the in-situ measurements. These values then overestimate the vertical and horizontal visibility as compared to the Secchi disk and diver sightings. The visibility products from SeaWiFS should be used on an experimental basis for Naval Operational Planning. It is recommended that the use of in-water diver reports noting variability of SeaWiFS visibility product estimates are necessary for validation and offers feedback to the research and development field for algorithm improvement. / Lieutenant, United States Navy

The occurrence of chitinolytic microbes and the colonisation and degradation of a native chitin substrate (squid pen) was studied in riverine, estuarine and marine aquatic environments m the Aberdeen area. Chitinolytic microbes were prevalent at all the sites (means: aerobic water 616ml-1, 2% of heterotrophs; anaerobic sediment 11560ml-1 0.8% of anaerobic heterotrophs). It was proposed that the chitinolytic numbers were directly influenced by the presence of chitinous material and indirectly influenced due to a heterotrophic response by organic/suspended matter levels. Hence chitinolytic numbers in the river and were largely influenced by allochthonous inputs while numbers in the sea were influenced by autochthonous production of organic and chitinous matter. From the results of a chitin assay of seawater it was extrapolated that 6.65x1013 metric tons of particulate chitin exist in the world's oceans. Chitin was found to degrade in all the sites studied. The annual rate ranged between 0.905% (river) to 0.074% (marine) squid pen day-1(approx 50mg seeded). The maximum rate recorded was 1.39% day at the river. At most of the sites the rate was positively correlated (P 0.05) with temperature. It was proposed that the marine annual rate would not cope with the annual chitin production and that degradation in the sea is mediated by the synergistic action of the chitinolytic microflora and fauna. The colonisation studies indicated that chitin was rapidly colonised at all the sites studied. The microbial numbers and biomass increased up to about 14 days after exposure, then levelled off and remained relatively constant for the remainder of each exposure period. It was proposed that the numbers of chitinolytic microbial colonisers remained relatively constant at each site studied throughout the year (i.e. changes in the degradation rate were due to variation in activity and not numbers), but the numbers and biomass of chitinolytic microbial colonisers was different between sites and this accounted for some of the variation in degradation rate recorded between sites. Samples with dense colonising biofilms and extensive filamentous growth were also characteristic of sites of relatively high chitin degradation.

Boston University. University Professors Program Senior theses. / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / 2031-01-02

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Thesis (Ph. D.)--Massachusetts Institutite of Technology and Woods Hole Oceanographic Institution, 1983. / Bibliography: p. 357-360.