Current Research Topics
1. Precise Acoustic Bathymetry
Precise acoustic bathymetry is needed to monitor shallow water navigation channels, dredging operations, underwater constructions, fisheries, and for other applications. Swath or multi-beam acoustic systems are being used for this task. The accuracy of multi-beam systems depends on precision with which we can calculate the travel time and travel path of the acoustic probing pulse transmitted at different angular directions. Efficient acoustic ray tracing algorithms have been developed and the effects of sound speed profile uncertainty on the accuracy of acoustic bathymetry have been evaluated. As the result of these investigations, a novel, hybrid bathymetric system has been proposed. The system uses a laser vertical bathymetry simultaneously with an acoustic multi-beam bathymetry for efficient and precise mapping of the ocean bottom.
Precise ocean depth charts are required for the development and management of ocean resources especially within the Exclusive Economic Zone (EEZ). Acoustic multi-beam and side-scan bathymetric systems are used for ocean depth measurement and bottom characterization. The error limit for depth measurement as specified by the International Hydrographic Organization is 1% for depth greater than 30 m and 0.3 m for depth less than 30 m. Several factors affect the accuracy of depth measurements. Some can be addressed using sophisticated electronics and signal processing techniques. However, the lack of precise sound speed profile information may lead to significant errors . In general, a sound pulse propagates along a curved path. If not accounted for, the bending of the acoustic ray may cause significant errors in acoustic distance and direction measurements. A number of acoustic ray tracing algorithms have been developed. All of these algorithms require knowledge of the sound speed profile. However, the sound speed profile in the ocean is a function of space and time and is not always available all the time during the survey. It is therefore necessary to investigate the effect of the uncertainty of the sound speed profile on the accuracy of depth and position measurements.
Research plan: Acoustic bathymetric and positioning systems are used in a number of underwater operations. However, acoustic ray bending has significant effects on the accuracy of distance and direction measurements. Analysis of the effects of sound speed profile uncertainty on the accuracy of an acoustic positioning system will be conducted, and error-correcting procedures will be developed. Remote measurement of the sound speed profile in the ocean is highly desirable from a logistic point of view. Methods described in suggest such a possibility. Investigations will be conducted to determine whether the accuracy offered by such measurements is sufficient for precise bathymetry and acoustic positioning. Possible implementations of these methods will be investigated. The research will be of interest to agencies responsible for bottom surveying such as the Canadian Hydrographic Service, as well as to manufacturers of acoustic mapping and positioning systems such as Simrad Ltd.
2. Underwater Communication and Beamforming
High-speed underwater communication in a shallow channel presents formidable difficulties due to long-lasting multi-path present in such a channel. The time-varying nature of such a channel calls for an adaptive transmitting and receiving scheme. A simple but effective model to assess multi-path interference has been developed and used to predict the performance of a digital communication system operating in a shallow underwater channel. A new concept of evaluating multi-path-corrupted signals has been proposed with the introduction of signal-to-multi-path ratio (SMR) parameter. This concept has been subsequently adopted by other researchers in the field and was the key idea in a recent Ph.D. thesis at the Technical University of Denmark. The channel equalization and directional transmitter/receiver can be used to mitigate multi-path in a shallow water channel. An adaptive equalizer with a variable number of taps has been proposed and its satisfactory performance was demonstrated using computer simulation. The results were documented in a recent Ph.D. thesis supervised by the applicant. The applicantís contributions were recognized in review papers written by experts in the field. An earlier concept of a Swept Carrier Communication proposed by the applicant has been recently revisited and was the basis for a Ph.D. thesis at the University of Western Australia.
There has been a growing activity in research pertaining to high-speed digital underwater acoustic communication. Underwater communication is needed for diverse applications that include the transmission of data from various oceanographic instruments such as hydrophones, video cameras, current meters, seismometers, sonars, etc., without instrument retrieval, control and telemetry of autonomous underwater vehicles (AUV), speech and video transmission in point-to-point links, and underwater networks. Recent research on a phase-coherent underwater acoustic communication system has demonstrated new possibilities for a high-data-rate communication system. Such a communication system offers better bandwidth utilization and transmission performance compared with incoherent schemes. However, the signal received through the underwater acoustic environment suffers phase shifts and amplitude fluctuations caused by multi-path propagation combined with Doppler shifts due to receiver and transmitter motions . Coherent communication requires rapid recovery and reliable tracking of the carrier phase. For this task, phase locked-loop (PLL) is commonly utilized.
Research Plan: We will continue and expand our research in the area of shallow water underwater acoustic communications. In order to achieve a reliable coherent communication system in such a channel, carrier synchronization issues will be further investigated. We will focus on M-PSK modulated signals because of their good bandwidth efficiency. The methods of removing modulating phases introduced by information sequences will be studied to track phase shifts introduced by channels. The adaptive algorithm for achieving rapid recovery and reliable tracking of phase shifts will be developed. Research on the applicability of the developed algorithm to underwater acoustic communication will be performed. Further investigations regarding acquisition and tracking performance will be carried out. Tracking performance will be investigated using phase error behavior and the bit error probability as a function of signal-to-noise ratio (SNR). Multi-path propagation due to surface and bottom reflections in a shallow water channel will be considered. The effects of Doppler shifts due to the movement of transmitter and/or receivers on the carrier synchronizer will be investigated. The results of this research will find application in the design of high-speed underwater acoustic communication systems. In several underwater and pattern synthesis applications (including underwater communications), there is a need to generate a beam having a desired pattern. Investigations of beamforming and pattern synthesis techniques have been conducted. Three new methods of beamforming have been developed. These techniques are more effective and less computationally intensive compared to other methods. The techniques have been successfully applied to more general applications and they provide powerful tools in the design of new types of acoustic arrays.
In underwater and other applications where large apertures are required, a number of array elements may fail. These failed elements produce undersized beam-forming artifacts and degrade system performance. Studies have been undertaken to provide guidelines for users facing these practical problems. Investigation of beam forming in the presence of element failure will be carried out. A new technique called pattern evolution will be used in conjunction with the already developed pattern synthesis methods. The focus of the work will be on removing undesired side-lobe contributions. The results will lead to an improvement of system performance and robustness. The research will be of interest to manufacturers of diverse sonar systems including navy sonars.
3. Acoustic Data Compression
Lossless data compression methods such as Huffman and arithmetic coding can be applied when the number of possible symbols to be coded is small. However, these methods are not directly applicable to the compression of digital sonar outputs where the number of symbols (sample values) are generally in the order of 106. A novel, simple and effective approach for loss-less compression has been proposed. This new coding scheme first decomposes the original data and then uses a bank of natural encoders. With this decomposition, a high coding efficiency can be achieved and with natural encoders, the implementation is fast and inexpensive. The new coding algorithm has the ability to adapt to different types of data. Therefore, real time, lossless compression can be effectively applied to diverse data types, including telemetry and instrument data, medical imagery, electrocardiogram, and sonar and radar data.
4. Ocean bottom identification using depth sounders
The possibility of remote sensing and reliable classification of bottom types and vegetation by acoustic means has important implications for geological exploration, underwater construction, and fisheries. Several systems have been developed and evaluated to accomplish this task. All of them use amplitude (envelope) information of the reflected acoustic signal to generate a set of statistical parameters subsequently used to classify the bottom. With this approach all information contained in the phase of the returning echo is lost. Also, echo returns from targets near the ocean bottom are usually treated as noise and are discarded. Such near-bottom echoes typically originate from biological organisms including vegetation and fish. There is a correlation between the type of vegetation, bottom topography, and bottom type. In this project, we will try to combine these elements in an attempt to classify the bottom and the bottom vegetation. Phase as well as amplitude of the acoustic reflections from the bottom and from targets near the bottom will be analyzed to determine the usefulness of this information for bottom and vegetation classification.
Research plan: This new area of research will be conducted in collaboration with Quester Tangent Corporation (Sidney) and the Institute of Oceanology (Poland). Acoustic data will be collected using a depth sounder operated simultaneously with an underwater camera. These data will be analyzed with the help of marine biologists and geologists to correlate the bottom type and vegetation type with acoustic returns.
5. Acoustic Applications to Fisheries
a. Fish identification
Acoustic methods augmented by biological sampling are used for assessment of fish stock in oceans, lakes, and rivers. Schools of fish often produce overlapping individual echoes. This does not allow for counting and for possible identification of the type of an individual fish. This project is aimed towards developing suitable techniques and signal processing algorithms to improve the resolution of acoustic systems used for fish detection and estimation.
b. Near bottom fish detection
Acoustic returns from weak targets near the ocean, lake, or river bottom are difficult to discriminate from strong bottom returns. Since some species of fish stay near the bottom, acoustic methods of detecting and estimating their abundance are, therefore, not reliable. This project is aimed towards devising methods to improve fish delectability by suitable signal processing.
c. Fish tracking
Acoustic navigation methods utilizing ultra-short base systems can track trajectories of individual targets in three dimensions. Such systems, called split-beam systems, have been used to track fish in lakes and rivers. The method is not always reliable for the simultaneous tracking of several fish. This project is aimed at improving the quality and reliability of tracking several fish in three dimensions.
Research plan: This new area of research will be conducted in collaboration with Pacific Biological Station. The acoustic data collected by the Station will be analyzed to test various algorithms to improve signal resolution and to suppress the unwanted echoes.
6. Electronic Palpometer
The applicant, working in collaboration with a local rheumatologist, has developed an instrument to quantitatively monitor pain threshold in arthritic patients. The device has been patented and has been used in several medical research establishments. A new nonlinear pressure-pain scale has been recently introduced in the second generation of the device. A spin-off company, Dolorometer System Inc., has been established to commercialize the invention and several units have been manufactured and sold or loaned. The patent rights to the invention have been assigned to the University of Victoria.