Environmental Information Content of Ocean Ambient Noise

In recent years, methods have been developed to estimate a variety of environmental parameters based on measurements of the ocean ambient noise. For example, noise has been used to estimate water depth using the passive fathometer technique and bottom loss estimated and used to invert for seabed parameters. There is also information in the noise about the water column sound speed, volume attenuation, and the sea-state. The Fisher information can be used to quantify the basic information available in the noise measurements and its inverse, the Cramér–Rao lower bound (CRLB), provides the lower limit on the variance of an unbiased estimator of a particular parameter. The CRLB can be used to study the feasibility of various measurement configurations and parameter sensitivities. In this paper, the CRLB is developed for ocean ambient noise and the environmental information contained in the measurements is determined. The CRLBs provide an estimate of the underlying information in the data, however, it is independent of the estimation methodology. This is useful to determine if a given estimation method is reaching the lower bound. Results illustrating the bounds as well as sensitivities and performance of estimators are demonstrated using both simulations and data

Advances in Aquatic Target Localization with Passive Sonar

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

A Two-hydrophone Range and Bearing Localization with Performance Analysis

An automated, passive algorithm for detecting and localizing small boats using two hydrophones mounted on the seabed is outlined. This extends previous work by Gebbie et al. [(2013). J. Acoust. Soc. Am. 134, EL77 − EL83] in which a similar two-hydrophone approach is used to produce an ambiguity surface of likely target locations leveraging multipath analysis and knowledge of the local bathymetry. The work presented here improves upon the prior approach using particle filtering to automate detection and localization processing. A detailed analysis has also been conducted to determine the conditions and limits under which the improved approach can be expected to yield accurate range and unambiguous bearing information. Experimental results in 12 m of water allow for a comparison of different separation distances between hydrophones, and the Bayesian Cramér-Rao lower bound is used to extrapolate the performance expected in 120 m water. This work demonstrates the conditions under which a low cost, passive, sparse array of hydrophones can provide a meaningful small boat detection and localization capability

Alternative Measurements and Processing for Extracting Seabed Information from Sea-surface Noise Correlations

In recent years, both theoretical and experimental results have shown that the noise generated at the sea-surface from wind and waves contains valuable information about the seabed. A verticalhydrophone array together with beamforming has been a particularly useful configuration for estimating seabed properties. By cross-correlating a vertically upward looking beam with a downward looking beam (the endfire directions), the bathymetry and seabed layering can be determined. However, there may be additional information about the seabed found by cross-correlating beams in directions away from vertical endfire. In this presentation, two new measurement and processing configurations will be considered: noise cross-correlation of beams from a vertical array in directions away from endfire and cross-correlation on a towed horizontal array. For the vertical array, data andmodeling show the existence of strong beam correlations coming from a direction consistent with the seabed critical angle. The towed horizontal array configuration, if possible, would provide an alternative to the vertical array for seabed surveying using noise. Measurements from data collected at several sites along with modeling will be used to explain the results from these new measurement and processing configurations

Implementation of the Australasian Teletrial Model: Translating idea into action using implementation science frameworks

Background: Despite Government investment, disparity in access to clinical trials continue between metropolitan and regional & rural sectors (RRR) in Australia and around the world. To improve trial access closer to home for RRR communities and rare cancer patients even in metro settings, the Australasian Teletrial Model (ATM) was developed by Clinical Oncology Society of Australia and implemented in four states. Aim of this paper is to describe the steps and processes involved in the development and implementation of ATM guided by implementation science frameworks. Method: Two implementation science frameworks namely iPARIHS and Strategic Implementation Framework were chosen to guide the project. Details of steps and processes were extracted from COSA final report. Results: ATM met the criteria for worthy innovation. For the development and implementation of the ATM, stakeholders were at national, statewide and clinical levels. A co-design with end-users and inclusion of key stakeholders in steering committees and advisory groups made the implementation smoother. Clinician levers including advocacy were useful to overcome system barriers. During the project, more patients, and clinicians at RRR participated in trials, more primary sites collaborated with RRR sites and more RRR sites gained trial capabilities. Conclusion: Pilot project achieved its objectives including improved access to patients locally, creation of linkages between metro and RRR sites and enhanced capabilities of and access to RRR sites. Implementation science frameworks were useful for identifying the necessary steps and processes at the outset. Ownership by governments and creation of streamlined regulatory systems would enable broader adoption