Alexander Gavrilov - Academia.edu (original) (raw)
Papers by Alexander Gavrilov
Acoustics Australia Australian Acoustical Society, 2014
The calving activity of the Antarctic ice shelves is one of the major indicators of global climat... more The calving activity of the Antarctic ice shelves is one of the major indicators of global climate change. Whereas massive calving events are well observed post factum from satellites, ice rifting and ice shelf breaks of smaller volumes are not monitored and statistically analysed. In-situ observations require great effort and expense and at present are not capable of providing long-term, real time monitoring of the Antarctic ice shelf disintegration. Remote acoustic observation using hydroacoustic receive systems, such as the hydroacoustic stations of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), can provide a cost-effective way to monitor ice rifting and calving in Antarctica. All the coastline of Eastern Antarctica from 0 0 to about 150 0 E can be observed from three IMS hydroacoustic stations in the Indian Ocean. Processing of the acoustic recordings on the station off Cape Leeuwin, Australia, has shown that a large number of the signals arrived from Antarctica have a pulse-like waveform and spectrograms revealing strong waveguide dispersion typical for long range propagation in a near-surface acoustic channel in the Southern Ocean south of the Antarctic Convergence. A comparison between the spectral characteristics of the received signals and the results of numerical modelling showed that those signals were emitted by short, pulse-like physical processes, which are most likely ice rifting and calving events.
Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to
This technical report briefly summarizes the results of the Arctic Climate Observations using Und... more This technical report briefly summarizes the results of the Arctic Climate Observations using Underwater Sound (ACOUS) experiment conducted in October 1998 -December 1999. The most important scientific achievements of the experiment are presented. The methods of acoustic inversion for acoustic thermometry in the Arctic Ocean are discussed using the conclusions that were made after processing and interpretation of the ACOUS data. Some technical issues are considered to bring about an improvement of the capability of the prospective acoustic thermometry systems, eliminating in particular certain weakness of the implementation of ACOUS experimental scheme.
The Journal of the Acoustical Society of America, 2015
This paper presents an empirical linear equation to predict peak pressure level of anthropogenic ... more This paper presents an empirical linear equation to predict peak pressure level of anthropogenic impulsive signals based on its correlation with the sound exposure level. The regression coefficients are shown to be weakly dependent on the environmental characteristics but governed by the source type and parameters. The equation can be applied to values of the sound exposure level predicted with a numerical model, which provides a significant improvement in the prediction of the peak pressure level. Part I presents the analysis for airgun arrays signals, and Part II considers the application of the empirical equation to offshore impact piling noise.
Acoustic data from the Arctic Climate Observations using Underwater Sound (ACOUS) experiment are ... more Acoustic data from the Arctic Climate Observations using Underwater Sound (ACOUS) experiment are analyzed to determine the correlation between acoustic propagation loss and the seasonal variability of sea ice thickness. The objective of this research is to provide long-term synoptic monitoring of sea ice thickness, an important global climate variable, using acoustic remote sensing. As part of the ACOUS program an autonomous acoustic source deployed northwest of Franz Josef Land transmitted tomographic signals at 20.5 Hz once every four days from October 1998 until December 1999. These signals were received on a vertical array in the Lincoln Sea 1250 km away. Two of the signals transmitted in April 1999 were received on a vertical array at ice camp APLIS in the Chukchi Sea north of Point Barrow, Alaska, at a distance of approximately 2720 km from the source. Temporal variations of the modal propagation loss are examined. The influence of ice parameters, variations of the sound speed profile, and modecoupling effects on the propagation losses of individual modes is studied. The experimental results arc compared to the results of the earlier experiments and the theoretical prediction using numerical modeling. PASC numbers: 43.30.Pc, 43.30. Hw, 43.30.Qd Potential Role of Underwater Acoustics in Studying Large-Scale Changes in the Arctic Ocean
Advances in experimental medicine and biology, 2016
The study of marine soundscapes is becoming widespread and the amount of data collected is increa... more The study of marine soundscapes is becoming widespread and the amount of data collected is increasing rapidly. Data owners (typically academia, industry, government, and defense) are negotiating data sharing and generating potential for data syntheses, comparative studies, analyses of trends, and large-scale and long-term acoustic ecology research. A problem is the lack of standards and commonly agreed protocols for the recording of marine soundscapes, data analysis, and reporting that make a synthesis and comparison of results difficult. We provide a brief overview of the components in a marine soundscape, the hard- and software tools for recording and analyzing marine soundscapes, and common reporting formats.
Both large-scale spatial variations of oceanographic characteristics and changes in the bottom to... more Both large-scale spatial variations of oceanographic characteristics and changes in the bottom topography can induce horizontal refraction. This study uses numerical modelling to investigate the horizontal refraction of low-frequency underwater sound propagating in the Indian and Southern Oceans, and the resulting effects on estimates of back-azimuths from the Comprehensive Test-ban Treaty (CTBT) hydroacoustic stations. It is shown that the horizontal wavenumbers of different modes in the deep water regions of the Southern Ocean within and beyond the Antarctic Convergence Zone (ACZ) have stronger horizontal gradients than those in the Indian Ocean. The deviation of bearing to the signal source from the two CTBT hydroacoustic stations off Cape Leeuwin (Western Australia) and off the Chagos Archipelago (BIOT) resulting from horizontal refraction does not exceed 0.20 in the most parts of the Indian Ocean. By contrast, strong horizontal wavenumber gradients in the high-latitude regions of the Southern Ocean and, especially, across the ACZ, cause the acoustic propagation path to deviate by as much as one degree from the geodetic line. This deviation depends strongly on the azimuth and range from the two CTBT hydroacoustic stations to signal sources located in the Southern Ocean beyond the ACZ.
The western and southern Australian continental shelf is mainly composed of a type of limestone c... more The western and southern Australian continental shelf is mainly composed of a type of limestone called calcarenite, overlain by a thin veneer of unconsolidated sediment. The shear wave speed in calcarenite is slightly less than the sound speed in water, which leads to some important, and rather unexpected propagation effects that are of considerable practical importance for such tasks as predicting the performance of passive sonar, and modelling the environmental impacts of marine seismic surveys. This paper introduces the physics of propagation in such an environment and provides a comparison between modelled and measured data. The implications for common modelling tasks are also discussed.
The Journal of the Acoustical Society of America, 2015
Numerical models of underwater sound propagation predict the energy of impulsive signals and its ... more Numerical models of underwater sound propagation predict the energy of impulsive signals and its decay with range with a better accuracy than the peak pressure. A semi-empirical formula is suggested to predict the peak pressure of man-made impulsive signals based on numerical predictions of their energy. The approach discussed by Galindo-Romero, Lippert, and Gavrilov [J. Acoust. Soc. Am. 138, in press (2015)] for airgun signals is modified to predict the peak pressure from offshore pile driving, which accounts for impact and pile parameters. It is shown that using the modified empirical formula provides more accurate predictions of the peak pressure than direct numerical simulations of the signal waveform.
Limestone seabeds with thin or non-existent coverings of unconsolidated sediment are common aroun... more Limestone seabeds with thin or non-existent coverings of unconsolidated sediment are common around the southern Australian continental shelf and often provide strong coupling between the sound wave in the water and the shear wave in the seabed. Sound reflection from such seabeds is very weak except at the p-wave critical angle, which results in the acoustic energy transmitted to long
As part of the Coastal Water Habitat Mapping (CWHM) project of the Cooperative Research Centre fo... more As part of the Coastal Water Habitat Mapping (CWHM) project of the Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management (Coastal CRC), a set of bathymetry and acoustic backscattering data was collected in Cockburn Sound, Western Australia in March 2004 in order to develop acoustic methods for seabed classification. The acoustic recordings were made over seabed areas of
MTS/IEEE Oceans 2001. An Ocean Odyssey. Conference Proceedings (IEEE Cat. No.01CH37295), 2001
In 1993 the USS Pargo made the first Submarine Science Expedition (SCICEX) to the Arctic Ocean. I... more In 1993 the USS Pargo made the first Submarine Science Expedition (SCICEX) to the Arctic Ocean. In April 1994 the first Transarctic Acoustic Propagation (TAP) experiment designed to measure Arctic Ocean temperature was conducted. SCICEX cruises to the Arctic followed annually from 1995 to 2000. Expendable CTD's and on some cruises standard CTD's were deployed along or close to the TAP acoustic section. In October of 1998 as part of the Arctic Climate Observations using Underwater Sound (ACOUS) program a source was deployed in the Franz Victoria Strait and a receive array was deployed in the Lincoln Sea. In April 1999 a second acoustic section was made across the Arctic when recordings of the ACOUS source were made at the APLIS Ice Camp in the Chukchi Sea as part of the support to SCICEX 1999. Comparisons between the acoustic sections and the SCICEX sections have shown that measurement of the average temperature in the Atlantic Layer is easily and very reliably accomplished using acoustic thermometry. Furthermore, all of these measurements have documented the steady rise in the temperature of the Atlantic Layer starting in the early 1990's. The SCICEX 2000 cruise is the last scheduled SCICEX cruise to the Arctic. Future scientific measurements in the Arctic by submarine will be accomplished intermittently on a not-tointerfere basis in conjunction with naval operations. Analysis of the first acoustic thermometry time series record from Oct. 1998 through Dec. 1999 is underway after the successful recovery of the ACOUS Lincoln Sea receive array in March 2001. SCICEX results and the acoustic thermometry time series results will be presented. Acoustic thermometry can provide a long-term reliable capability for monitoring Arctic Ocean temperature and other variables including the thermocline depth. This can be accomplished by including acoustic receivers and sources on moorings that are currently under consideration for deployment in the Arctic under the proposed Study of Environmental Arctic Change (SEARCH) program.
Measurements of the transmission loss of airgun signals from an offshore seismic exploration surv... more Measurements of the transmission loss of airgun signals from an offshore seismic exploration survey were made in 2011 in the western part of Bass Strait, Australia, as part of an 8-month sea noise monitoring and blue whale tracking program supported by Origin Energy. The measurements were made using an array of four autonomous sea noise recorders equipped with single hydrophones and deployed on the seafloor on the continental shelf not far from the continental slope. The distances from the hydrophones to the airgun array varied from 38 km to nearly 75 km. A review of the airgun signals received on the hydrophone array revealed that their waveform and spectral characteristics were atypical of a low-frequency impulsive signal propagated in shallow water over the continental shelf. The acoustic energy in the received signals was noticeable only in three relatively narrow frequency bands below 40 Hz. Moreover, airgun shots from some seismic transects were not detected in sea noise recordings. An explanation of such peculiar sound propagation in this area of the strait is suggested in this paper based on results of numerical modelling and some supplementary data on seafloor properties.
Underwater noise measurements were made over a period of 5 months within the Fremantle Inner Harb... more Underwater noise measurements were made over a period of 5 months within the Fremantle Inner Harbour (from April 1 st -July 2 nd , and July 26 th -August 20 th , 2010). Noise was recoded from a range of sources, including vessel traffic which was intense at periods, noise from trains and vehicles passing over a nearby bridge, machinery noise from regular operation of the Fremantle Port, and pile driving (either vibratory pile driving, impact pile driving, or both) recorded during wharf construction over approximately 57 days, (mainly during the months of May, July, and August). All sources recorded are common to a busy and expanding port. Noise levels in the port during periods when pile driving was not occurring were typically between 110 and 140 dB re 1Pa 2 (mean squared pressure). Vibratory pile and impact pile driving increased noise levels within the Inner Harbour. Biological noises were also detected in the recordings. Dominant biological sources were snapping shrimp, followed by mulloway (Argyrosomus japonicus) chorusing in early to mid-April, and grunts from other fish species detected throughout the recordings. Indo-Pacific bottlenose dolphin (Tursiops aduncus) whistles were also detected in the noise logger recordings.
Seagrass distribution and other measures of seagrass condition have been used as broad scale biol... more Seagrass distribution and other measures of seagrass condition have been used as broad scale biological indicators of marine and estuarine health. To date the distribution of seagrass in the Swan-Canning Estuary has been assessed based on aerial photographs, which is ineffective in deep, turbid waters. Sidescan sonar systems (SSS) provide acceptable results in a much wider range of environmental conditions, particularly as they are not affected by the turbidity or water depth of the river. A SSS was successfully used to collect backscatter data from 10 survey areas in the Swan-Canning Estuary ranging from 0.5 -15m in depth. The SSS was able to distinguish areas of seagrass from bare sediment. A simple threshold classification method was used to produce geo-referenced habitat maps from each of the 10 areas showing the predicted distribution of low and high density seagrass, sand, mud and rock. The SSS is considered cost-effective and efficient for similar studies in other shallow water estuaries provided it is conducted in conjunction with ground-truthing at selected reference points.
This document has emerged from the Coastal Water Habitat Mapping (CWHM) Project of the Cooperativ... more This document has emerged from the Coastal Water Habitat Mapping (CWHM) Project of the Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management. Material from the three year CWHM Project, together with selected information from other sources, is included in the document. The document also incorporates much of a report (Penrose and Siwabessy 2001) commissioned in 2001 by the Marine Conservation Branch of the Western Australia Department of Conservation and Land Management (CALM). Contributing authors to the present document have, in most cases, focussed on one aspect of the acoustic techniques reviewed, as outlined below. There has also been, however, considerable interaction between contributing authors during its development, and most chapters have had inputs from several of the author team. The final compilation and editing has been carried out by J. Penrose assisted by J. Siwabessy. A valuable companion document to this review is an extensive bibliography of ...
Progress in Oceanography, 2015
The Perth
Multibeam sonar (MBS) systems are recognised as one of the most effective tools available to map ... more Multibeam sonar (MBS) systems are recognised as one of the most effective tools available to map and characterise the seafloor as they can provide co-located high-resolution bathymetry and acoustic backscatter characteristics from a wide swath across a vessel's track. While the production of bathymetry maps from MBS is well developed, processing and analysis of MBS backscatter data has not yet reached its full potential. One of the main issues has been the variation of backscatter strength with incidence. A new approach to producing images of backscatter properties developed by the authors, called an 'Angle Cube', is compared with a standard method for correcting for incident angle. The resulting backscatter and classified maps show that advantages of using the angle cube method in processing multibeam sonar data for benthic habitat mapping.
Acoustics Australia Australian Acoustical Society, 2014
The calving activity of the Antarctic ice shelves is one of the major indicators of global climat... more The calving activity of the Antarctic ice shelves is one of the major indicators of global climate change. Whereas massive calving events are well observed post factum from satellites, ice rifting and ice shelf breaks of smaller volumes are not monitored and statistically analysed. In-situ observations require great effort and expense and at present are not capable of providing long-term, real time monitoring of the Antarctic ice shelf disintegration. Remote acoustic observation using hydroacoustic receive systems, such as the hydroacoustic stations of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), can provide a cost-effective way to monitor ice rifting and calving in Antarctica. All the coastline of Eastern Antarctica from 0 0 to about 150 0 E can be observed from three IMS hydroacoustic stations in the Indian Ocean. Processing of the acoustic recordings on the station off Cape Leeuwin, Australia, has shown that a large number of the signals arrived from Antarctica have a pulse-like waveform and spectrograms revealing strong waveguide dispersion typical for long range propagation in a near-surface acoustic channel in the Southern Ocean south of the Antarctic Convergence. A comparison between the spectral characteristics of the received signals and the results of numerical modelling showed that those signals were emitted by short, pulse-like physical processes, which are most likely ice rifting and calving events.
Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to
This technical report briefly summarizes the results of the Arctic Climate Observations using Und... more This technical report briefly summarizes the results of the Arctic Climate Observations using Underwater Sound (ACOUS) experiment conducted in October 1998 -December 1999. The most important scientific achievements of the experiment are presented. The methods of acoustic inversion for acoustic thermometry in the Arctic Ocean are discussed using the conclusions that were made after processing and interpretation of the ACOUS data. Some technical issues are considered to bring about an improvement of the capability of the prospective acoustic thermometry systems, eliminating in particular certain weakness of the implementation of ACOUS experimental scheme.
The Journal of the Acoustical Society of America, 2015
This paper presents an empirical linear equation to predict peak pressure level of anthropogenic ... more This paper presents an empirical linear equation to predict peak pressure level of anthropogenic impulsive signals based on its correlation with the sound exposure level. The regression coefficients are shown to be weakly dependent on the environmental characteristics but governed by the source type and parameters. The equation can be applied to values of the sound exposure level predicted with a numerical model, which provides a significant improvement in the prediction of the peak pressure level. Part I presents the analysis for airgun arrays signals, and Part II considers the application of the empirical equation to offshore impact piling noise.
Acoustic data from the Arctic Climate Observations using Underwater Sound (ACOUS) experiment are ... more Acoustic data from the Arctic Climate Observations using Underwater Sound (ACOUS) experiment are analyzed to determine the correlation between acoustic propagation loss and the seasonal variability of sea ice thickness. The objective of this research is to provide long-term synoptic monitoring of sea ice thickness, an important global climate variable, using acoustic remote sensing. As part of the ACOUS program an autonomous acoustic source deployed northwest of Franz Josef Land transmitted tomographic signals at 20.5 Hz once every four days from October 1998 until December 1999. These signals were received on a vertical array in the Lincoln Sea 1250 km away. Two of the signals transmitted in April 1999 were received on a vertical array at ice camp APLIS in the Chukchi Sea north of Point Barrow, Alaska, at a distance of approximately 2720 km from the source. Temporal variations of the modal propagation loss are examined. The influence of ice parameters, variations of the sound speed profile, and modecoupling effects on the propagation losses of individual modes is studied. The experimental results arc compared to the results of the earlier experiments and the theoretical prediction using numerical modeling. PASC numbers: 43.30.Pc, 43.30. Hw, 43.30.Qd Potential Role of Underwater Acoustics in Studying Large-Scale Changes in the Arctic Ocean
Advances in experimental medicine and biology, 2016
The study of marine soundscapes is becoming widespread and the amount of data collected is increa... more The study of marine soundscapes is becoming widespread and the amount of data collected is increasing rapidly. Data owners (typically academia, industry, government, and defense) are negotiating data sharing and generating potential for data syntheses, comparative studies, analyses of trends, and large-scale and long-term acoustic ecology research. A problem is the lack of standards and commonly agreed protocols for the recording of marine soundscapes, data analysis, and reporting that make a synthesis and comparison of results difficult. We provide a brief overview of the components in a marine soundscape, the hard- and software tools for recording and analyzing marine soundscapes, and common reporting formats.
Both large-scale spatial variations of oceanographic characteristics and changes in the bottom to... more Both large-scale spatial variations of oceanographic characteristics and changes in the bottom topography can induce horizontal refraction. This study uses numerical modelling to investigate the horizontal refraction of low-frequency underwater sound propagating in the Indian and Southern Oceans, and the resulting effects on estimates of back-azimuths from the Comprehensive Test-ban Treaty (CTBT) hydroacoustic stations. It is shown that the horizontal wavenumbers of different modes in the deep water regions of the Southern Ocean within and beyond the Antarctic Convergence Zone (ACZ) have stronger horizontal gradients than those in the Indian Ocean. The deviation of bearing to the signal source from the two CTBT hydroacoustic stations off Cape Leeuwin (Western Australia) and off the Chagos Archipelago (BIOT) resulting from horizontal refraction does not exceed 0.20 in the most parts of the Indian Ocean. By contrast, strong horizontal wavenumber gradients in the high-latitude regions of the Southern Ocean and, especially, across the ACZ, cause the acoustic propagation path to deviate by as much as one degree from the geodetic line. This deviation depends strongly on the azimuth and range from the two CTBT hydroacoustic stations to signal sources located in the Southern Ocean beyond the ACZ.
The western and southern Australian continental shelf is mainly composed of a type of limestone c... more The western and southern Australian continental shelf is mainly composed of a type of limestone called calcarenite, overlain by a thin veneer of unconsolidated sediment. The shear wave speed in calcarenite is slightly less than the sound speed in water, which leads to some important, and rather unexpected propagation effects that are of considerable practical importance for such tasks as predicting the performance of passive sonar, and modelling the environmental impacts of marine seismic surveys. This paper introduces the physics of propagation in such an environment and provides a comparison between modelled and measured data. The implications for common modelling tasks are also discussed.
The Journal of the Acoustical Society of America, 2015
Numerical models of underwater sound propagation predict the energy of impulsive signals and its ... more Numerical models of underwater sound propagation predict the energy of impulsive signals and its decay with range with a better accuracy than the peak pressure. A semi-empirical formula is suggested to predict the peak pressure of man-made impulsive signals based on numerical predictions of their energy. The approach discussed by Galindo-Romero, Lippert, and Gavrilov [J. Acoust. Soc. Am. 138, in press (2015)] for airgun signals is modified to predict the peak pressure from offshore pile driving, which accounts for impact and pile parameters. It is shown that using the modified empirical formula provides more accurate predictions of the peak pressure than direct numerical simulations of the signal waveform.
Limestone seabeds with thin or non-existent coverings of unconsolidated sediment are common aroun... more Limestone seabeds with thin or non-existent coverings of unconsolidated sediment are common around the southern Australian continental shelf and often provide strong coupling between the sound wave in the water and the shear wave in the seabed. Sound reflection from such seabeds is very weak except at the p-wave critical angle, which results in the acoustic energy transmitted to long
As part of the Coastal Water Habitat Mapping (CWHM) project of the Cooperative Research Centre fo... more As part of the Coastal Water Habitat Mapping (CWHM) project of the Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management (Coastal CRC), a set of bathymetry and acoustic backscattering data was collected in Cockburn Sound, Western Australia in March 2004 in order to develop acoustic methods for seabed classification. The acoustic recordings were made over seabed areas of
MTS/IEEE Oceans 2001. An Ocean Odyssey. Conference Proceedings (IEEE Cat. No.01CH37295), 2001
In 1993 the USS Pargo made the first Submarine Science Expedition (SCICEX) to the Arctic Ocean. I... more In 1993 the USS Pargo made the first Submarine Science Expedition (SCICEX) to the Arctic Ocean. In April 1994 the first Transarctic Acoustic Propagation (TAP) experiment designed to measure Arctic Ocean temperature was conducted. SCICEX cruises to the Arctic followed annually from 1995 to 2000. Expendable CTD's and on some cruises standard CTD's were deployed along or close to the TAP acoustic section. In October of 1998 as part of the Arctic Climate Observations using Underwater Sound (ACOUS) program a source was deployed in the Franz Victoria Strait and a receive array was deployed in the Lincoln Sea. In April 1999 a second acoustic section was made across the Arctic when recordings of the ACOUS source were made at the APLIS Ice Camp in the Chukchi Sea as part of the support to SCICEX 1999. Comparisons between the acoustic sections and the SCICEX sections have shown that measurement of the average temperature in the Atlantic Layer is easily and very reliably accomplished using acoustic thermometry. Furthermore, all of these measurements have documented the steady rise in the temperature of the Atlantic Layer starting in the early 1990's. The SCICEX 2000 cruise is the last scheduled SCICEX cruise to the Arctic. Future scientific measurements in the Arctic by submarine will be accomplished intermittently on a not-tointerfere basis in conjunction with naval operations. Analysis of the first acoustic thermometry time series record from Oct. 1998 through Dec. 1999 is underway after the successful recovery of the ACOUS Lincoln Sea receive array in March 2001. SCICEX results and the acoustic thermometry time series results will be presented. Acoustic thermometry can provide a long-term reliable capability for monitoring Arctic Ocean temperature and other variables including the thermocline depth. This can be accomplished by including acoustic receivers and sources on moorings that are currently under consideration for deployment in the Arctic under the proposed Study of Environmental Arctic Change (SEARCH) program.
Measurements of the transmission loss of airgun signals from an offshore seismic exploration surv... more Measurements of the transmission loss of airgun signals from an offshore seismic exploration survey were made in 2011 in the western part of Bass Strait, Australia, as part of an 8-month sea noise monitoring and blue whale tracking program supported by Origin Energy. The measurements were made using an array of four autonomous sea noise recorders equipped with single hydrophones and deployed on the seafloor on the continental shelf not far from the continental slope. The distances from the hydrophones to the airgun array varied from 38 km to nearly 75 km. A review of the airgun signals received on the hydrophone array revealed that their waveform and spectral characteristics were atypical of a low-frequency impulsive signal propagated in shallow water over the continental shelf. The acoustic energy in the received signals was noticeable only in three relatively narrow frequency bands below 40 Hz. Moreover, airgun shots from some seismic transects were not detected in sea noise recordings. An explanation of such peculiar sound propagation in this area of the strait is suggested in this paper based on results of numerical modelling and some supplementary data on seafloor properties.
Underwater noise measurements were made over a period of 5 months within the Fremantle Inner Harb... more Underwater noise measurements were made over a period of 5 months within the Fremantle Inner Harbour (from April 1 st -July 2 nd , and July 26 th -August 20 th , 2010). Noise was recoded from a range of sources, including vessel traffic which was intense at periods, noise from trains and vehicles passing over a nearby bridge, machinery noise from regular operation of the Fremantle Port, and pile driving (either vibratory pile driving, impact pile driving, or both) recorded during wharf construction over approximately 57 days, (mainly during the months of May, July, and August). All sources recorded are common to a busy and expanding port. Noise levels in the port during periods when pile driving was not occurring were typically between 110 and 140 dB re 1Pa 2 (mean squared pressure). Vibratory pile and impact pile driving increased noise levels within the Inner Harbour. Biological noises were also detected in the recordings. Dominant biological sources were snapping shrimp, followed by mulloway (Argyrosomus japonicus) chorusing in early to mid-April, and grunts from other fish species detected throughout the recordings. Indo-Pacific bottlenose dolphin (Tursiops aduncus) whistles were also detected in the noise logger recordings.
Seagrass distribution and other measures of seagrass condition have been used as broad scale biol... more Seagrass distribution and other measures of seagrass condition have been used as broad scale biological indicators of marine and estuarine health. To date the distribution of seagrass in the Swan-Canning Estuary has been assessed based on aerial photographs, which is ineffective in deep, turbid waters. Sidescan sonar systems (SSS) provide acceptable results in a much wider range of environmental conditions, particularly as they are not affected by the turbidity or water depth of the river. A SSS was successfully used to collect backscatter data from 10 survey areas in the Swan-Canning Estuary ranging from 0.5 -15m in depth. The SSS was able to distinguish areas of seagrass from bare sediment. A simple threshold classification method was used to produce geo-referenced habitat maps from each of the 10 areas showing the predicted distribution of low and high density seagrass, sand, mud and rock. The SSS is considered cost-effective and efficient for similar studies in other shallow water estuaries provided it is conducted in conjunction with ground-truthing at selected reference points.
This document has emerged from the Coastal Water Habitat Mapping (CWHM) Project of the Cooperativ... more This document has emerged from the Coastal Water Habitat Mapping (CWHM) Project of the Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management. Material from the three year CWHM Project, together with selected information from other sources, is included in the document. The document also incorporates much of a report (Penrose and Siwabessy 2001) commissioned in 2001 by the Marine Conservation Branch of the Western Australia Department of Conservation and Land Management (CALM). Contributing authors to the present document have, in most cases, focussed on one aspect of the acoustic techniques reviewed, as outlined below. There has also been, however, considerable interaction between contributing authors during its development, and most chapters have had inputs from several of the author team. The final compilation and editing has been carried out by J. Penrose assisted by J. Siwabessy. A valuable companion document to this review is an extensive bibliography of ...
Progress in Oceanography, 2015
The Perth
Multibeam sonar (MBS) systems are recognised as one of the most effective tools available to map ... more Multibeam sonar (MBS) systems are recognised as one of the most effective tools available to map and characterise the seafloor as they can provide co-located high-resolution bathymetry and acoustic backscatter characteristics from a wide swath across a vessel's track. While the production of bathymetry maps from MBS is well developed, processing and analysis of MBS backscatter data has not yet reached its full potential. One of the main issues has been the variation of backscatter strength with incidence. A new approach to producing images of backscatter properties developed by the authors, called an 'Angle Cube', is compared with a standard method for correcting for incident angle. The resulting backscatter and classified maps show that advantages of using the angle cube method in processing multibeam sonar data for benthic habitat mapping.