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• 1. [Article] Head Wave Correlations in Ambient Noise

  Ambient ocean noise is processed with a vertical line array to reveal coherent time-separated arrivals suggesting the presence of head wave multipath propagation. Head waves, which are critically propagating ...

  Citation × Citation Citation Abstract Copy Title: Head Wave Correlations in Ambient Noise Author: Gebbie, John Thomas, Siderius, Martin Year: 2016 Ambient ocean noise is processed with a vertical line array to reveal coherent time-separated arrivals suggesting the presence of head wave multipath propagation. Head waves, which are critically propagating water waves created by seabed waves traveling parallel to the water-sediment interface, can propagate faster than water-only waves. Such eigenrays are much weaker than water-only eigenrays, and are often completely overshadowed by them. Surface-generated noise is different whereby it amplifies the coherence between head waves and critically propagating water-only waves, which is measured by cross-correlating critically steered beams. This phenomenon is demonstrated both experimentally and with a full wave simulation. Title: Head Wave Correlations in Ambient Noise Author: Gebbie, John Thomas, Siderius, Martin Year: 2016 Ambient ocean noise is processed with a vertical line array to reveal coherent time-separated arrivals suggesting the presence of head wave multipath propagation. Head waves, which are critically propagating water waves created by seabed waves traveling parallel to the water-sediment interface, can propagate faster than water-only waves. Such eigenrays are much weaker than water-only eigenrays, and are often completely overshadowed by them. Surface-generated noise is different whereby it amplifies the coherence between head waves and critically propagating water-only waves, which is measured by cross-correlating critically steered beams. This phenomenon is demonstrated both experimentally and with a full wave simulation. Close

• 2. [Article] Effects of Sea-Surface Conditions on Passive Fathometry and Bottom Characterization

  Recently, a method has been developed that exploits the correlation properties of the ocean’s ambient noise to measure water depth (a passive fathometer) and seabed layering [M. Sideriuset al., J. Acoust. ...

  Citation × Citation Citation Abstract Copy Title: Effects of Sea-Surface Conditions on Passive Fathometry and Bottom Characterization Author: Means, Steven L., Siderius, Martin Year: 2009 Recently, a method has been developed that exploits the correlation properties of the ocean’s ambient noise to measure water depth (a passive fathometer) and seabed layering [M. Sideriuset al., J. Acoust. Soc. Am.120, 1315–1323 (2006)]. This processing is based on the cross-correlation between the surface noise and the echo return from the seabed. To quantitatively study the dependency between processing and environmental factors such as wind speed, measurements were made using a fixed hydrophone array while simultaneously characterizing the environment. The measurements were made in 2006 in the shallow waters (25m)approximately 75km off the coast of Savannah, GA. A Navy tower about 100m from the array was used to measure wind speed and to observe the sea-surface using a video camera. Data were collected in various environmental conditions with wind speeds ranging from 5 to 21m/s and wave heights of 1–3.4m. The data are analyzed to quantify the dependency of passive fathometer results on wind speeds, wave conditions, and averaging times. One result shows that the seabed reflection is detectable even in the lowest wind conditions. Further, a technique is developed to remove the environmental dependency so that the returns estimate seabed impedance. Title: Effects of Sea-Surface Conditions on Passive Fathometry and Bottom Characterization Author: Means, Steven L., Siderius, Martin Year: 2009 Recently, a method has been developed that exploits the correlation properties of the ocean’s ambient noise to measure water depth (a passive fathometer) and seabed layering [M. Sideriuset al., J. Acoust. Soc. Am.120, 1315–1323 (2006)]. This processing is based on the cross-correlation between the surface noise and the echo return from the seabed. To quantitatively study the dependency between processing and environmental factors such as wind speed, measurements were made using a fixed hydrophone array while simultaneously characterizing the environment. The measurements were made in 2006 in the shallow waters (25m)approximately 75km off the coast of Savannah, GA. A Navy tower about 100m from the array was used to measure wind speed and to observe the sea-surface using a video camera. Data were collected in various environmental conditions with wind speeds ranging from 5 to 21m/s and wave heights of 1–3.4m. The data are analyzed to quantify the dependency of passive fathometer results on wind speeds, wave conditions, and averaging times. One result shows that the seabed reflection is detectable even in the lowest wind conditions. Further, a technique is developed to remove the environmental dependency so that the returns estimate seabed impedance. Close

• 3. [Article] Glider-based Seabed Characterization using Natural-made Ambient Noise

  Seabed characteristics (geoacoustic properties and scattering strength) are critical parameters for sonar performance predictions. However, this bottom information is considered very difficult and expensive ...

  Citation × Citation Citation Abstract Copy Title: Glider-based Seabed Characterization using Natural-made Ambient Noise Author: Nielsen, Peter L., Siderius, Martin, Muzi, Lanfranco Year: 2015 Seabed characteristics (geoacoustic properties and scattering strength) are critical parameters for sonar performance predictions. However, this bottom information is considered very difficult and expensive to achieve in the scientific community. In this report, an efficient method for inferring the seabed properties is presented; it relies on a previous methodology using long moored or drifting hydrophone arrays. Results from sea trials demonstrate the feasibility of using the technique by deploying a hybrid autonomous underwater vehicle hosting a unique hydrophone array consisting of a five-element vertical line array and a four-element tetrahedral array. Seabed reflection and layering properties are estimated from sea surface generated ambient noise acquired during two trials in different shallow-water areas. Results from numerical modeling, data analysis and experimental measurements are presented with emphasis on comparing the seabed characterization at different locations with different bottom properties. The results obtained from both experiments demonstrate the potential of using autonomous underwater vehicles for seabed characterization and surface vessel tracking. Title: Glider-based Seabed Characterization using Natural-made Ambient Noise Author: Nielsen, Peter L., Siderius, Martin, Muzi, Lanfranco Year: 2015 Seabed characteristics (geoacoustic properties and scattering strength) are critical parameters for sonar performance predictions. However, this bottom information is considered very difficult and expensive to achieve in the scientific community. In this report, an efficient method for inferring the seabed properties is presented; it relies on a previous methodology using long moored or drifting hydrophone arrays. Results from sea trials demonstrate the feasibility of using the technique by deploying a hybrid autonomous underwater vehicle hosting a unique hydrophone array consisting of a five-element vertical line array and a four-element tetrahedral array. Seabed reflection and layering properties are estimated from sea surface generated ambient noise acquired during two trials in different shallow-water areas. Results from numerical modeling, data analysis and experimental measurements are presented with emphasis on comparing the seabed characterization at different locations with different bottom properties. The results obtained from both experiments demonstrate the potential of using autonomous underwater vehicles for seabed characterization and surface vessel tracking. Close

• 4. [Article] Passive Acoustical Oceanography

  Acoustical Oceanography includes the use of both active and passive acoustic systems to measure various properties of the ocean environment. Active methods use a specifically designed and controlled sound ...

  Citation × Citation Citation Abstract Copy Title: Passive Acoustical Oceanography Author: Siderius, Martin Year: 2016 Acoustical Oceanography includes the use of both active and passive acoustic systems to measure various properties of the ocean environment. Active methods use a specifically designed and controlled sound projector while passive methods exploit naturally occurring ocean sounds such as breaking waves, ship noise, or marine mammal vocalizations. Historically, active methods have been the preferred choice when precise propagation times or calibrated sound levels are important. However, passive sensing has a strong appeal due in part to the ease in which listening-only systems can be deployed. There have been a number of advances in passive sensing even for cases where propagation times and sound levels are of interest. For example, it has been shown that surface wave noise can be used to measure vertical propagation times through the seabed and water column. More recently, there is experimental evidence that indicates noise correlations may also be used to determine horizontal propagation times in the seabed. Although replacing controlled projectors with noise sources is an attractive option there are limitations to how and when noise can be used this way. These limitations as well as experimental and modeling results from surface and ship noise will be described in this presentation. Title: Passive Acoustical Oceanography Author: Siderius, Martin Year: 2016 Acoustical Oceanography includes the use of both active and passive acoustic systems to measure various properties of the ocean environment. Active methods use a specifically designed and controlled sound projector while passive methods exploit naturally occurring ocean sounds such as breaking waves, ship noise, or marine mammal vocalizations. Historically, active methods have been the preferred choice when precise propagation times or calibrated sound levels are important. However, passive sensing has a strong appeal due in part to the ease in which listening-only systems can be deployed. There have been a number of advances in passive sensing even for cases where propagation times and sound levels are of interest. For example, it has been shown that surface wave noise can be used to measure vertical propagation times through the seabed and water column. More recently, there is experimental evidence that indicates noise correlations may also be used to determine horizontal propagation times in the seabed. Although replacing controlled projectors with noise sources is an attractive option there are limitations to how and when noise can be used this way. These limitations as well as experimental and modeling results from surface and ship noise will be described in this presentation. Close

• 5. [Article] 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. ...

  Citation × Citation Citation Abstract Copy Title: A Two-hydrophone Range and Bearing Localization with Performance Analysis Author: Gebbie, John Thomas, Siderius, Martin, Allen, John S., III Year: 2015 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. Title: A Two-hydrophone Range and Bearing Localization with Performance Analysis Author: Gebbie, John Thomas, Siderius, Martin, Allen, John S., III Year: 2015 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. Close

• 6. [Article] Frequency Based Noise Coherence-Function Extension and Application to Passive Bottom-Loss Estimation

  Accurate modeling of acoustic propagation in the ocean waveguide is important to SONAR-performance prediction. Particularly in shallow waters, a crucial contribution to the total transmission loss is the ...

  Citation × Citation Citation Abstract Copy Title: Frequency Based Noise Coherence-Function Extension and Application to Passive Bottom-Loss Estimation Author: Muzi, Lanfranco, Siderius, Martin, Nielsen, Peter L. Year: 2016 Accurate modeling of acoustic propagation in the ocean waveguide is important to SONAR-performance prediction. Particularly in shallow waters, a crucial contribution to the total transmission loss is the bottom refection loss, which can be estimated passively by beamforming the natural surface-noise acoustic field recorded by a vertical line array of hydrophones. However, the performance in this task of arrays below 2 m of length is problematic for frequencies below 10 kHz" role="presentation" style="display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative;">10 kHz10 kHz It is shown in this paper that, when the data are free of interference from sources other than wind and wave surface noise, data from a shorter array can be used to approximate the coherence function of a longer array. This improves the angular resolution of the estimated bottom loss, often making use of data at frequencies above the array design frequency. Application to simulated and experimental data shows that the technique, rigorously justified for a halfspace bottom, is effective also on more complex bottom types. Dispensing with active sources, small autonomous underwater vehicles equipped with short arrays can be envisioned as compact, efficient seabed-characterization systems. The proposed technique is shown to improve significantly the reflection-loss estimate of an array that would be a candidate for such application. Title: Frequency Based Noise Coherence-Function Extension and Application to Passive Bottom-Loss Estimation Author: Muzi, Lanfranco, Siderius, Martin, Nielsen, Peter L. Year: 2016 Accurate modeling of acoustic propagation in the ocean waveguide is important to SONAR-performance prediction. Particularly in shallow waters, a crucial contribution to the total transmission loss is the bottom refection loss, which can be estimated passively by beamforming the natural surface-noise acoustic field recorded by a vertical line array of hydrophones. However, the performance in this task of arrays below 2 m of length is problematic for frequencies below 10 kHz" role="presentation" style="display: inline; line-height: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px 2px 0px 0px; margin: 0px; position: relative;">10 kHz10 kHz It is shown in this paper that, when the data are free of interference from sources other than wind and wave surface noise, data from a shorter array can be used to approximate the coherence function of a longer array. This improves the angular resolution of the estimated bottom loss, often making use of data at frequencies above the array design frequency. Application to simulated and experimental data shows that the technique, rigorously justified for a halfspace bottom, is effective also on more complex bottom types. Dispensing with active sources, small autonomous underwater vehicles equipped with short arrays can be envisioned as compact, efficient seabed-characterization systems. The proposed technique is shown to improve significantly the reflection-loss estimate of an array that would be a candidate for such application. Close

• 7. [Article] Effects of Ocean Thermocline Variability on Noncoherent Underwater Acoustic Communications

  The performance of acoustic modems in the ocean is strongly affected by the oceanenvironment. A storm can drive up the ambient noise levels, eliminate a thermocline by wind mixing, and whip up violent ...

  Citation × Citation Citation Abstract Copy Title: Effects of Ocean Thermocline Variability on Noncoherent Underwater Acoustic Communications Author: Siderius, Martin, Porter, Michael B., Hursky, Paul, McDonald, Vincent Year: 2007 The performance of acoustic modems in the ocean is strongly affected by the oceanenvironment. A storm can drive up the ambient noise levels, eliminate a thermocline by wind mixing, and whip up violent waves and thereby break up the acoustic mirror formed by theocean surface. The combined effects of these and other processes on modem performance are not well understood. The authors have been conducting experiments to study these environmental effects on various modulation schemes. Here the focus is on the role of the thermocline on a widely used modulation scheme (frequency-shift keying). Using data from a recent experiment conducted in 100-m-deep water off the coast of Kauai, HI, frequency-shift-key modulation performance is shown to be strongly affected by diurnal cycles in the thermocline. There is dramatic variation in performance (measured by bit error rates) between receivers in the surface duct and receivers in the thermocline. To interpret the performance variations in a quantitative way, a precise metric is introduced based on a signal-to-interference-noise ratio that encompasses both the ambient noise and intersymbol interference. Further, it will be shown that differences in the fading statistics for receivers in and out of the thermocline explain the differences in modem performance. Title: Effects of Ocean Thermocline Variability on Noncoherent Underwater Acoustic Communications Author: Siderius, Martin, Porter, Michael B., Hursky, Paul, McDonald, Vincent Year: 2007 The performance of acoustic modems in the ocean is strongly affected by the oceanenvironment. A storm can drive up the ambient noise levels, eliminate a thermocline by wind mixing, and whip up violent waves and thereby break up the acoustic mirror formed by theocean surface. The combined effects of these and other processes on modem performance are not well understood. The authors have been conducting experiments to study these environmental effects on various modulation schemes. Here the focus is on the role of the thermocline on a widely used modulation scheme (frequency-shift keying). Using data from a recent experiment conducted in 100-m-deep water off the coast of Kauai, HI, frequency-shift-key modulation performance is shown to be strongly affected by diurnal cycles in the thermocline. There is dramatic variation in performance (measured by bit error rates) between receivers in the surface duct and receivers in the thermocline. To interpret the performance variations in a quantitative way, a precise metric is introduced based on a signal-to-interference-noise ratio that encompasses both the ambient noise and intersymbol interference. Further, it will be shown that differences in the fading statistics for receivers in and out of the thermocline explain the differences in modem performance. Close

• 8. [Article] Wavelet-Coupled Machine Learning Methods for Drought Forecast Utilizing Hybrid Meteorological and Remotely-Sensed Data

  In this study, a statistical drought early warning method is proposed using novel machine learning algorithms, with the inclusion of multiple drought-related attributes from precipitation, satellite-derived ...

  Citation × Citation Citation Abstract Copy Title: Wavelet-Coupled Machine Learning Methods for Drought Forecast Utilizing Hybrid Meteorological and Remotely-Sensed Data Author: Tan, R., Perkowski, Marek Year: 2015 In this study, a statistical drought early warning method is proposed using novel machine learning algorithms, with the inclusion of multiple drought-related attributes from precipitation, satellite-derived land cover vegetation indices, and surface discharge. The forecast is made for the long-term hydrological drought in the region of Central Valley, California. The wavelet transform analysis is employed in combination with support vector regression and artificial neural network algorithms for improving the drought prediction effectiveness. The performance of the drought prediction is evaluated using three statistical metrics: Coefficient of Determination (R2 ), Root-Mean-Square Error (RMSE), and Mean-Absolute-Error (MAE). The results clearly indicate that using hybrid precipitation and satellite remotelysensed data, the proposed wavelet-coupled machine learning method can effectively predict long-term drought in the area of Central Valley California, over a lead time of 3 to 6 months, which is crucial for agricultural planning, reservoir management, and authorities’ allocation of water resources. Title: Wavelet-Coupled Machine Learning Methods for Drought Forecast Utilizing Hybrid Meteorological and Remotely-Sensed Data Author: Tan, R., Perkowski, Marek Year: 2015 In this study, a statistical drought early warning method is proposed using novel machine learning algorithms, with the inclusion of multiple drought-related attributes from precipitation, satellite-derived land cover vegetation indices, and surface discharge. The forecast is made for the long-term hydrological drought in the region of Central Valley, California. The wavelet transform analysis is employed in combination with support vector regression and artificial neural network algorithms for improving the drought prediction effectiveness. The performance of the drought prediction is evaluated using three statistical metrics: Coefficient of Determination (R2 ), Root-Mean-Square Error (RMSE), and Mean-Absolute-Error (MAE). The results clearly indicate that using hybrid precipitation and satellite remotelysensed data, the proposed wavelet-coupled machine learning method can effectively predict long-term drought in the area of Central Valley California, over a lead time of 3 to 6 months, which is crucial for agricultural planning, reservoir management, and authorities’ allocation of water resources. Close

• 9. [Article] 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 ...

  Citation × Citation Citation Abstract Copy Title: Advances in Aquatic Target Localization with Passive Sonar Author: Gebbie, John Thomas Year: 2014 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. Title: Advances in Aquatic Target Localization with Passive Sonar Author: Gebbie, John Thomas Year: 2014 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. Close