Nicos Pelavas

Autonomous underwater vehicle localization using the acoustic tracking system

Operator peace-of-mind during Autonomous Underwater Vehicle (AUV) missions is dependent on the ability to localize the vehicle. During launch and recovery phases this capability is particularly important. Defence R&D Canada (DRDC) Atlantic has designed and built a long-range tracking system for the International Submarine Engineering Explorer class AUVs. The acoustic tracking system (ATS) enables an operator on a loud icebreaker platform to determine the position of the AUVs at ranges up to 30 km. An acoustic projector, mounted on the AUV, emits a hyperbolic frequency modulated (HFM) chirp at a preset time interval. A small, directional, acoustic receiving array mounted near the stern of the icebreaker, accurately synchronized with the remote projector, receives signals from the distant AUV. Matched filter processing is used to determine the time of flight of the transmitted chirp. A beamforming algorithm applied to the data provides bearing and elevation angle estimates for the received signals. A ray tr...

Short range localization of Autonomous Underwater Vehicles

The melting of Arctic ice and the resulting access provided to previously inaccessible regions of the Arctic Ocean has lead to various Arctic exploratory efforts by a number of nations. Canada is collecting Arctic bathymetry survey data in order to define the extent of its continental shelf in accordance with the United Nations Convention on the Law of the Sea. Supporting the collection of Arctic bathymetry data are two International Submarine Engineering, Explorer class, Autonomous Underwater Vehicles (AUVs). In order to reduce the risk inherent with under-ice AUV operations, Defence Research and Development Canada - Atlantic has designed and built a homing system and a localization system for each of the vehicles. The homing system enables the AUV to find its way to the source of an underwater acoustic signal at ranges in excess of 50 km. In this paper we shall present the localization system, which utilizes a field of acoustic modems allowing the AUV to determine its three dimensional position relative to a reference point. Enhancements to the localization method shall be discussed. These include improvements both at the surface station and the implementation of the algorithm in the vehicle. Lastly, short range localization results from the 2010 Arctic survey trial near Borden Island are presented.

Acoustic propagation in the Strait of Georgia

In recent years, there has been a proliferation of Ocean Observing Systems (OOS) along with a wide distribution of their associated data products. The collected data support scientific research, industry, and government organizations by providing long term measurements of biological, chemical, and physical properties of the ocean environment. However, the collection and distribution of underwater acoustic data poses a potential security risk for naval vessels operating in the vicinity of OOS. The Canadian Forces Maritime Experimental and Test Ranges (CFMETR) provide an underwater tracking facility for naval tests, and are approximately 50 km from hydrophones of the Victoria Experimental Network Under the Sea (VENUS) observatory. Under an existing CFMETR-VENUS agreement, data are diverted during certain naval tests. In order to minimize the frequency of these data diversions, a study is being conducted to investigate acoustic propagation in the Strait of Georgia. The results of acoustic modeling and measur...

Directionality of ambient noise measurements in Barrow Strait of the Canadian Arctic

In August 2012, a field trial was carried out in Barrow Strait south of Gascoyne Inlet in the vicinity of 74.630 N 91.340 W. Underwater acoustic data was collected using a JASCO Autonomous Multichannel Acoustic Recorder (AMAR) and in-house designed sensor systems called Starfish Cubes. The Starfish Cubes were deployed twice, at different locations, each for one week duration and at depths of approximately 110 m. The Cubes consist of seven hydrophones with 1 m spacing and geometrically configured as three cross-dipoles with a central hydrophone, and have an operational frequency range of 5—750 Hz. During the trial 400 and 500 Hz tones were transmitted from discrete locations at various ranges. By using a beamforming method the tones were used to determine the orientation of the Starfish Cubes during their data collection periods. This enables investigation of the horizontal and vertical directionality of ambient noise. Unique localized sources contributing to the ambient noise are discussed such as a nearb...

Measurements and modeling of transmission loss variability in Barrow Strait

During the summer of 2012, a field trial was held in Barrow Strait, south of Devon Island in the Canadian Arctic. The trial included a set of acoustic transmission loss experiments recorded on Starfish Sensor Cubes, which include a 1-m cube of seven hydrophones operating in the frequency range of 5 - 750 Hz. The transmission loss runs consisted of 10-minute and 20-minute duration transmissions of 400 Hz and 500 Hz tones made at a discrete set of distances up to 60 km from the recorders. Supporting environmental measurements included sets of CTD (conductivity-temperature-depth) profiles and bathymetric measurements. The effects of the measured environmental properties and variability are investigated via propagation modeling, and compared to the experimental data acquired during these experiments.

Results of the development of a long-range acoustic homing system for autonomous underwater vehicles

Modified international submarine engineering (ISE) explorer AUVs with an endurance of over 400 km are being used to aid in the mapping of the under-ice Arctic seafloor. The explorers are equipped with a DRDC-developed acoustic homing system built into the AUV nose cone. The acoustic receiver consists of seven digital hydrophones arranged in a tri-axis cross-dipole array. A controller/data processor located within the AUV pressure hull handles the real-time acoustic arrival azimuth and elevation estimation, as well as the control and calculations for an on-demand short-range three dimensional (3-D) localization system, and the control of vehicle telemetry data flow. The processor and array consume less than 2 W. A small, easily transportable, DRDC-designed acoustic transducer provides a powerful acoustic homing signal. Using the homing system, the vehicles were able to locate an acoustic beacon at a randomly drifting Ice Camp from a range in excess of 50 km (100-km ranges possible). The design, development...

Linear drift error for cornerstone autonomous underwater vehicle

Autonomous underwater vehicles (AUVs) have a promising future in their use of collecting bathymetric data in remote regions of the Arctic Ocean. In accordance with the United Nations Convention on the Law of the Sea, Defence Research & Development Canada Atlantic has partnered with Natural Resources Canada (NRCan) and Department of Fisheries and Oceans to use AUVs in support of Canadas Arctic claim. In this article, we investigate the AUV linear drift error that accumulates as a result of a misalignment between the Inertial Navigation Unit and the Doppler Velocity Log. Data collected during the 2010 Cornerstone Arctic field trial is used to quantify the linear drift error associated with one of the AUVs. The linear drift error was determined to be 0.67% to stern and 0.21% to starboard, and this result was then applied to correct the track for the AUV survey mission.

A robust phase gradient bearing estimation algorithm for a tri-axis cross-dipole acoustic array, with application to a long range autonomous underwater vehicle homing and tracking system

A Phase Gradient bearing estimation algorithm was developed as part of a Long Range Acoustic Bearing (LRAB) homing system for an Autonomous Underwater Vehicle (AUV). The algorithm was designed for a tri-axis cross-dipole acoustic array with seven digital hydrophones. The algorithm estimates the bearing and elevation angles to a continuous wave (CW) signal from a beacon source. The algorithm directly estimates the three Cartesian components of the incoming signal wave-vector from estimated cross-spectra between the hydrophone elements. The algorithm is robust against hydrophone failure, and every hydrophone in the array is used to estimate each component of the incoming wave-vector.