<p>Reverberation and clutter are two of the principle obstacles to active sonar target detection in shallow water. Diffuse seabed backscatter can obscure low energy target returns, while clutter discretes, specific features of the sea floor, produce temporally compact returns which may be mistaken for targets of interest. Detecting weak targets in the presence of reverberation and discriminating water column targets from bottom clutter are thus critical to good performance in active sonar. Both problems are addressed in this thesis using the time-frequency interference pattern described by a constant known as the waveguide invariant which summarizes in a scalar parameter the dispersive properties of the ocean environment. </p><p>Conventional active sonar detection involves constant false alarm rate (CFAR) normalization of the reverberation return which does not account for the frequency-selective fading in a wideband pulse caused by multipath propagation. An alternative to conventional reverberation estimation is presented, motivated by striations observed in time-frequency analysis of active sonar data. A mathematical model for these reverberation striations is derived using waveguide invariant theory. This model is then used to motivate waveguide invariant reverberation estimation which involves averaging the time-frequency spectrum along these striations. An evaluation of this reverberation estimate using real Mediterranean data is given and its use in a generalized likelihood ratio test (GLRT) based CFAR detector is demonstrated. CFAR detection using waveguide invariant reverberation estimates is shown to outperform conventional cell-averaged and frequency-invariant CFAR detection methods in shallow water environments producing strong reverberation returns which exhibit the described striations. Results are presented on simulated and real Mediterranean data from the SCARAB98 experiment. </p><p>The ability to discriminate between water column targets and clutter discretes is vital to maintaining low false alarm rates in active sonar. Moreover, because of the non-stationarity of the active sonar return, classification is most typically achieved using a single snapshot of test data. As an aid to classification, the waveguide invariant property is used to derive multiple snapshots by uniformly sub-sampling the short-time Fourier transform (STFT) coefficients of a single ping of wideband active sonar data. The sub-sampled target snapshots are used to define a waveguide-invariant spectral density matrix (WI-SDM) which allows the application of adaptive matched-filtering based approaches for target depth classification. Depth classification is performed by a waveguide-invariant minimum variance filter (WI-MVF) which matches the observed WI-SDM to depth-dependent signal replica vectors generated from a normal mode model. Robustness to environmental mismatch is achieved by adding environmental perturbation constraints (EPC) and averaging the signal replica vectors over the unknown channel parameters. Simulation and real data results from the SCARAB98, CLUTTER07, and CLUTTER09 experiments in the Mediterranean Sea are presented to illustrate the approach.</p> / Dissertation

The focus of this research was the practical application, inventory, and analysis of scenic resources of the marine environment. From an international perspective, the concept of establishing marine parks and preserves was traced and shown to be a recent phenomenon in an effort to protect pristine and unique marine areas. Unfortunately, the inclusion of marine scenic resources as a distinct element in the site planning and site design management process is at present negligible. This research presents a systematic scenic resource inventory and scenic preference testing using the Q-sort method of underwater photographic examples from three case study areas: Key Largo National Marine Sanctuary, Florida, St. Croix, US Virgin Islands and Jervis Bay, New South Wales Australia. Over three hundred volunteers rated fifteen underwater photographs from each case study area in an attempt to determine the predictive factors for scenic resource quality. Demographic information was collected from each volunteer in terms of sex, age, occupation, education, place of residence and diving experience. These background characteristics were evaluated in terms of their effect on scenic preference ratings using correlation analysis. It was demonstrated that these background factors had no significant influence on scenic preference rating. Nine seascape dimensions were selected and analyzed using multiple regression to determine if certain physiographic variables influenced preference rating. It was determined that color, marine fauna, marine flora, and water clarity were the most influential factors affecting scenic preference rating. Based on these scenic preference results, a proposed site management plan was demonstrated for each case study that could be a model for future scenic resource assessment.

Amplification of low-light-level optical images is important for extending the range of lidar systems that image and detect objects in the atmosphere and underwater. The use of range-gating to produce images of particular range bins is also important in minimizing the image degradation due to light that is scattered backward from aerosols, smoke, or water along the imaging path. For practical lidar systems that must be operated within sight of unprotected observers, eye safety is of the utmost importance. This dissertation describes a new type of eye-safe, range-gated lidar sensing element based on Solid-state Raman Image Amplification (SSRIA) in a solid-state optical crystal. SSRIA can amplify low-level images in the eye-safe infrared at 1.556 μm with gains up to 106 with the addition of only quantum-limited noise. The high gains from SSRIA can compensate for low quantum efficiency detectors and can reduce the need for detector cooling. The range-gate of SSRIA is controlled by the pulsewidth of the pump laser and can be as short as 30-100 cm, using pump pulses of 2-6.7 nsec FWHM. A rate equation theoretical model is derived to help in the design of short pulsed Raman lasers. A theoretical model for the quantum noise properties of SSRIA is presented. SSRIA results in higher SNR images throughout a broad range of incident light levels, in contrast to the increasing noise factor with reduced gain in image intensified CCD's. A theoretical framework for the optical resolution of SSRIA is presented and it is shown that SSRIA can produce higher resolution than ICCD's. SSRIA is also superior in rejecting unwanted sunlight background, further increasing image SNR. Lastly, SSRIA can be combined with optical pre-filtering to perform optical image processing functions such as high-pass filtering and automatic target detection/recognition. The application of this technology to underwater imaging, called Marine Raman Image Amplification (MARIA) is also discussed. MARIA operates at a wavelength of 563 nm, which passes most efficiently through coastal ocean waters. The imaging resolution of MARIA in the marine environment can be superior to images produced by laser line scan or standard range-gated imaging systems.

We consider a ship subject to kinematic, dynamic, and moment equations and steered via the rudder under the assumptions that the rudder angle and rudder angle time rate are subject to upper and lower bounds. We formulate and solve four Mayer problems of optimal control, the optimization criterion being the minimum time. Also, we formulate and solve four Chebyshev problems of optimal control, the optimization criterion being the maximization with respect to the control history of the minimum value with respect to time of the distance between two identical ships, one maneuvering and one moving in a predetermined way. Problems P1 and P2 deal with course change maneuvers. In Problem P1, a ship initially in quasi-steady state must reach the final point with a given yaw angle and zero yaw angle time rate. Problem P2 differs from Problem P1 in that quasi-steady state is required at the final point. Problems P3 and P4 deal with sidestep maneuvers. In Problem P3, a ship initially in quasi-steady state must reach the final point with a given lateral distance, zero yaw angle, and zero yaw angle time rate. Problem P4 differs from Problem P3 in that quasi-steady state is required at the final point. Problems P5 and P6 deal with collision avoidance maneuvers without cooperation, while Problems P7 and P8 deal with collision avoidance maneuvers with cooperation. In Problems P5 and P7, the maneuvering ship must reach the final point with a given lateral distance, zero yaw angle, and zero yaw angle time rate. Problems P6 and P8 differ from Problems P5 and P7 in that quasi-steady state is required at the final point. The above Mayer problems and Chebyshev problems, transformed into Lagrange problems via suitable transformations, are solved via the sequential gradient-restoration algorithm in conjunction with a new singularity avoiding transformation which accounts for the bounds on rudder angle and rudder angle time rate. The optimal control histories involve multiple subarcs along which either the rudder angle is kept at one of the extreme positions or the rudder angle time rate is held at one of the two extreme values. If quasi-steady state is not required at the final point, the total number of subarcs ranges from 4 to 8, depending on the particular problem. If quasi-steady state is required at the final point, the total number of subarcs ranges from 6 to 10, depending on the particular problem: the higher number of subarcs, is due to the additional requirements that the lateral velocity and rudder angle vanish at the final point.

Thesis (Ph.D.)--University of California, San Diego, 2005. / (UnM)AAI3208810. Advisers: Lisa A. Levin; A. Aristides Yayanos. Source: Dissertation Abstracts International, Volume: 67-03, Section: B, page: 1244.

The LOST2 system is a new accurate underwater positioning system that nonlinearly combines parts of dead-reckoning, acoustic-based positioning, and terrain-based positioning. The system is composed of two major subsystems, a system observer and a constrained extended Kalman filter. Inputs to the system are as follows: (1) high resolution bathymetry, (2) measured ocean depth at the position of the vessel, (3) measured or estimated vessel velocity, (4) slant range to and position of a known point, and (5) an initial prediction of the vessel's location. The system development, simulation studies, results from sea trials and some suggestions for future work are presented. The system is capable of providing position estimates with the same degree of accuracy as present methods, with significantly less hardware. These results prove the concept of the system as a new method to position underwater vessels / acase@tulane.edu

The fate and occurrence of Giardia and Cryptosporidium were studied in the marine environment to assess their potential for transmission since their transmission to swimmers in fresh waters has been previously documented. The first part of this study was designed to determine the occurrence of Giardia and Cryptosporidium at bathing beaches within the vicinity of an outfall discharging primary treated sewage into Mamala Bay, Hawaii. Sites were monitored monthly and quarterly for parasites by passing 400 liters of marine water through a spun polyproplyene fiber filter. Giardia and Cryptosporidium were detected in primary treated sewage from the Sand Island sewage treatment plant which discharges into Mamala Bay at concentrations of 2,560 cysts and 216 oocysts/liter, respectively. Ala Wai Canal as well as the bathing beaches within the vicinity of the outfall were also found to contain the parasites. The survival of Giardia in marine water was studied in direct sunlight and the dark in marine waters (33- to 35-ppt salinity), canal water (28-ppt salinity) and in phosphate-buffered saline (8-ppt) at 18 to 28°C. Giardia muris was inactivated by 3-logs in the presence of sunlight in marine and canal waters. In comparison, Giardia survive up to 6 hours in PBS under the same conditions. Overall, it appears that salinity and sunlight quickly inactivate Giardia cysts. Thus, Giardia would pose a threat only if the cysts reach the bathing beaches within a few hours. The last phase of this project was designed to develop a more efficient method of collection of cysts and oocysts from water. Methods for the concentration of enteric viruses, Giardia and Cryptosporidium from water requires the use of two different types of filters. This study compared the efficiency of their concentration from tap water and tertiary treated wastewater with a polypropylene fiber cartridge, and the Filterite electronegative and the 1MDS Virosorb electropositive microporous filters. Results indicated that the overall efficiency was greatest for the Filterite filter for both Giardia and Cryptosporidium (p = 0.000762 and p = 0.067069, respectively); and in addition they are easier and faster to process than the polypropylene-wound parasite filter.