Small-scale glaciological processes can drive large-scale ice sheet behavior but remain underrepo... more Small-scale glaciological processes can drive large-scale ice sheet behavior but remain underreported due to a paucity of surface elevation measurements in remote polar regions. Satellite images provide a relatively long record of spatially dense surface observations, which allow us to investigate changes in ice sheet topography on the spatial scales of 1–10 km. Inferring surface topography from satellite images is an established technique, but in previous efforts, strict requirements for illumination conditions and image quality have led to a great quantity of discarded data. Relaxing quality requirements and fitting linear trends to the time series of image-derived surface topography allow inclusion of more total signal and enable blending data from multiple platforms. As a proof of concept, we combine 121 MODerate-resolution Imaging Spectroradiometer images to develop a 250-m resolution map of surface elevation change at Totten Glacier, Antarctica achieving a 1-σ uncertainty of 0.22 m a −1 for a 15-year period. Our method of repeat photoclinometry agrees with repeat laser altimetry while revealing clear patterns of surface elevation change associated with ice advection, channelized ice shelf basal melt, subglacial lake activity, and possible grounding line migration.
Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, ... more Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations.
Previous studies of Totten Ice Shelf have employed surface velocity measurements to estimate its ... more Previous studies of Totten Ice Shelf have employed surface velocity measurements to estimate its mass balance and understand its sensitivities to interannual changes in climate forcing. However, displacement measurements acquired over timescales of days to weeks may not accurately characterize long-term flow rates wherein ice velocity fluctuates with the seasons. Quantifying annual mass budgets or analyzing interannual changes in ice velocity requires knowing when and where observations of glacier velocity could be aliased by subannual variability. Here, we analyze 16 years of velocity data for Totten Ice Shelf, which we generate at subannual resolution by applying feature-tracking algorithms to several hundred satellite image pairs. We identify a seasonal cycle characterized by a spring to autumn speedup of more than 100 m yr −1 close to the ice front. The amplitude of the seasonal cycle diminishes with distance from the open ocean, suggesting the presence of a resistive back stress at the ice front that is strongest in winter. Springtime acceleration precedes summer surface melt and is not attributable to thinning from basal melt. We attribute the onset of ice shelf acceleration each spring to the loss of buttressing from the breakup of seasonal landfast sea ice.
The Journal of the Acoustical Society of America, 2009
ABSTRACT Acoustic resonances are exploited in many natural and human‐made systems, and demonstrat... more ABSTRACT Acoustic resonances are exploited in many natural and human‐made systems, and demonstrations of the phenomena have been presented previously [Greene et al., J. Acoust. Soc. Am. 124, 2568 (2008); Argo IV et al., J. Acoust. Soc. Am. 125, 2625 (2009)]. In practice, resonance is always accompanied by energy loss, which limits the maximum excursion of a system. When sufficiently large, this loss can alter the resonance frequency of the system. An air bubble in water is an example of a lossy acoustic resonator and is well‐suited for demonstrating acoustic damping in the Listen Up paradigm. For the proposed demonstration, students will observe the resonance of a water‐filled drinking glass by striking it with a metal spoon to produce a strong ringing sound. They will then introduce damping into the system by using a stream of water to entrain bubbles which will deaden the ringing response of the system. The primary mechanism for the acoustic energy dissipation is conversion into heat during bubble oscillation. An explanation of this process is presented with a detailed description of the proposed experiment.
The Journal of the Acoustical Society of America, 2009
ABSTRACT One goal of Project Listen Up is to enhance children's understanding of acoustic... more ABSTRACT One goal of Project Listen Up is to enhance children's understanding of acoustics through engagement in basic acoustics experiments. This work proposes an experiment that examines the resonant frequencies of an air column. Equipment for this experiment consists of a small tunable oscillator circuit connected to a loudspeaker, which can also be used for other experiments in the kit. The experimenter will provide a cardboard tube, rubber band, plastic wrap, and sand. Resonance is demonstrated by placing the loudspeaker at the base of the tube, covering the top of the tube with a plastic wrap membrane, and placing sand grains on top of the membrane. As frequency is adjusted, the sand grains are excited at the resonance frequencies of the tube. Frequencies at which sand motion is observed can be compared to a simple algebraic model, which relates the length of the tube to the resonance frequencies of the system. An optional advanced experimental track investigates the effect of varying the length of the tube. This experiment develops intuition for the relationship between frequency and wavelength and builds understanding of resonant systems.
The Journal of the Acoustical Society of America, 2008
ABSTRACT The Listen Up project seeks to develop an educational booklet and apparatus that will be... more ABSTRACT The Listen Up project seeks to develop an educational booklet and apparatus that will be used to foster interest in acoustics and teach basic acoustical concepts to middle school students. The packaged kit must be low cost; hence this experiment uses a 16 oz plastic water bottle as a Helmholtz resonator, a disposable syringe, and an inexpensive pitch pipe. Understanding the Helmholtz resonator is fundamental to many applications in acoustics. A simple algebraic model of the device, derived from a mechanical mass-spring analogy, relates the volume of air in the bottle to the resonance frequency of the system, and hence the pitch that is produced when one blows over the bottle opening. The volume of air inside the bottle can be easily and accurately controlled by adding water with a graduated syringe. The dependence of pitch on the volume of air in the bottle can be systematically demonstrated, and the validity of the model can be checked by comparing the sound produced to musical notes from the pitch pipe. This experiment yields a physical understanding of a common acoustical phenomenon and inspires further interest and study of more complex phenomena.
The Journal of the Acoustical Society of America, 2011
ABSTRACT The unique molecular structures of gas hydrates result in curious acoustic properties, w... more ABSTRACT The unique molecular structures of gas hydrates result in curious acoustic properties, which have yet to be adequately described. Understanding the acoustic behavior of stable and dissociating gas hydrates in liquids is vital for their localization and quantification using seismic or echosounding techniques. Further, with improved characterization of the acoustic properties of gas hydrates and bubbly liquids containing methane gas, acoustic methods may become an invaluable tool for monitoring hydrate dissociation and determining the magnitude of its effects on climate change. Acoustic properties of gassy substances are known to have a strong dependence on excitation frequency; however, tabulated values of hydrate material properties are most often measured in the frequency range of hundreds of kilohertz, while natural hydrate deposits and gas seeps are typically surveyed at seismic frequencies several orders of magnitude below laboratory measurement frequencies. This presentation details laboratory experiments in which a low-frequency (10 Hz to 10 kHz) acoustic resonator apparatus was used to measure (a) sound speeds of bubbly liquids containing ideal and real gases and (b) bulk moduli and dissociation pressures of natural structure I and structure II gas hydrate samples. [Work supported by the Office of Naval Research.]
The Journal of the Acoustical Society of America, 2010
ABSTRACT Cold seeps are gas vents that are found in the ocean, often along continental shelves ne... more ABSTRACT Cold seeps are gas vents that are found in the ocean, often along continental shelves near sediment-borne methane hydrates. Methane hydrates and methane gas seeps are of particular interest both for their potential use as an energy source and for their possible contribution to global climate change. This work is an initial step toward passively locating cold seeps and quantifying their gas flow rates using acoustic remote sensing techniques. Results are presented from laboratory experiments in which gas fluxes were determined from the radiated acoustic signature of a model seep. The physical principle that supports the technique and its accuracy will be discussed. [Work supported by ONR.].
The Journal of the Acoustical Society of America, 2009
ABSTRACT Methane hydrates occur naturally on the ocean bottom and in the upper layers of sediment... more ABSTRACT Methane hydrates occur naturally on the ocean bottom and in the upper layers of sediment on continental shelves. Seismic surveying could be used to locate methane hydrates; however, their low‐frequency acoustic properties are not well‐known. In addition, these properties can vary dramatically depending on whether the methane is in a gas or solid phase. As a step toward better understanding the three‐phase case of gassy sediments in water, the two‐phase case of methane gas bubbles in water was investigated. Wood’s equation is often used to model sound propagation in bubbly liquids and has been widely verified by experiments at atmospheric pressure. However, there is little information in the literature verifying the validity of Wood’s equation at high pressures. Low‐frequency (0.5–10‐kHz), resonator‐based sound speedmeasurements were obtained for air bubbles in water and methane bubbles in water under pressures ranging from 1 to 10 atm at room temperature. The results are presented and compared to the predictions of Wood’s equation. [Work sponsored by ONR.]
The Journal of the Acoustical Society of America, 2010
ABSTRACT The didgeridoo is an ancient Aboriginal instrument traditionally crafted from Eucalyptus... more ABSTRACT The didgeridoo is an ancient Aboriginal instrument traditionally crafted from Eucalyptus trees which have been hollowed out by termites. The instrument is an excellent example of a simple one-dimensional acoustic resonator with a fundamental resonance corresponding to one-half wavelength. Today, the ubiquity and low cost of PVC pipes make didgeridoos inexpensive, easy to find, and trivial to construct from materials found at any hardware store. Students will have fun learning to make sounds with the instrument-perhaps they will even learn the technique of circular breathing-all while exploring fundamental principles of acoustics. As further investigation students can hum as they play, resulting in "beats, the speed of which can be adjusted by changing the pitch of the hum.
We present the Antarctic Mapping Tools package, an open-source MATLAB toolbox for analysis and pl... more We present the Antarctic Mapping Tools package, an open-source MATLAB toolbox for analysis and plotting of Antarctic geospatial datasets. This toolbox is designed to streamline scientific workflow and maximize repeatability through functions which allow fully scripted data analysis and mapping. Data access is facilitated by several dataset-specific plugins which are freely available online. An open architecture has been chosen to encourage users to develop and share plugins for future Antarctic geospatial datasets. This toolbox includes functions for coordinate transformations, flight line or ship track analysis, and data mapping in georeferenced or projected coordinates. Each function is thoroughly documented with clear descriptions of function syntax alongside examples of data analysis or display using Antarctic geospatial data. The Antarctic Mapping Tools package is designed for ease of use and allows users to perform each step of data processing including raw data import, data analysis, and creation of publication-quality maps, wholly within the numerical environment of MATLAB.
Data graphics shape the way science is communicated, and the color schemes we employ can either... more Data graphics shape the way science is communicated, and the color schemes we employ can either faithfully represent or tacitly obscure the data a figure is intended to convey (Tufte, 1983). Tasteful use of color can make data graphics visually appealing and can draw viewers in, engaging the audience and encouraging further inspection of a figure. But wherever color is used to represent numerical values, its role transitions from a mere aesthetic nicety to carrying the responsibility of conveying data honestly and accurately. Yet, biases introduced by some common colormaps have gone widely unrecognized within the oceanographic community. Here, we describe the pitfalls of some commonly used colormaps, provide guidelines on effective, accurate colormap selection, and present a suite of perceptually uniform cmocean colormaps that have been designed for oceanographic data display. The cmocean package is available across multiple software programs, including MATLAB, Python, R, Generic Mapping Tools, and Ocean Data Viewer.
Passive acoustic techniques are of interest as a low-power means of quantifying underwater point-... more Passive acoustic techniques are of interest as a low-power means of quantifying underwater point-source gas ebullition. Toward the development of systems for logging natural seep activity, laboratory experiments were performed that exploited the bubble's Minnaert natural frequency for the measurement of gas flow from a model seep. Results show agreement among acoustic, optical, and gas trap ebullition measurements over the range of emission rates from 0 to 10 bubbles per second. A mathematical model is proposed to account for the real gas behavior of bubbles which cannot be approximated as ideal, such as methane at marine depths exceeding 30 m.
Small-scale glaciological processes can drive large-scale ice sheet behavior but remain underrepo... more Small-scale glaciological processes can drive large-scale ice sheet behavior but remain underreported due to a paucity of surface elevation measurements in remote polar regions. Satellite images provide a relatively long record of spatially dense surface observations, which allow us to investigate changes in ice sheet topography on the spatial scales of 1–10 km. Inferring surface topography from satellite images is an established technique, but in previous efforts, strict requirements for illumination conditions and image quality have led to a great quantity of discarded data. Relaxing quality requirements and fitting linear trends to the time series of image-derived surface topography allow inclusion of more total signal and enable blending data from multiple platforms. As a proof of concept, we combine 121 MODerate-resolution Imaging Spectroradiometer images to develop a 250-m resolution map of surface elevation change at Totten Glacier, Antarctica achieving a 1-σ uncertainty of 0.22 m a −1 for a 15-year period. Our method of repeat photoclinometry agrees with repeat laser altimetry while revealing clear patterns of surface elevation change associated with ice advection, channelized ice shelf basal melt, subglacial lake activity, and possible grounding line migration.
Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, ... more Totten Glacier in East Antarctica has the potential to raise global sea level by at least 3.5 m, but its sensitivity to climate change has not been well understood. The glacier is coupled to the ocean by the Totten Ice Shelf, which has exhibited variable speed, thickness, and grounding line position in recent years. To understand the drivers of this interannual variability, we compare ice velocity to oceanic wind stress and find a consistent pattern of ice-shelf acceleration 19 months after upwelling anomalies occur at the continental shelf break nearby. The sensitivity to climate forcing we observe is a response to wind-driven redistribution of oceanic heat and is independent of large-scale warming of the atmosphere or ocean. Our results establish a link between the stability of Totten Glacier and upwelling near the East Antarctic coast, where surface winds are projected to intensify over the next century as a result of increasing atmospheric greenhouse gas concentrations.
Previous studies of Totten Ice Shelf have employed surface velocity measurements to estimate its ... more Previous studies of Totten Ice Shelf have employed surface velocity measurements to estimate its mass balance and understand its sensitivities to interannual changes in climate forcing. However, displacement measurements acquired over timescales of days to weeks may not accurately characterize long-term flow rates wherein ice velocity fluctuates with the seasons. Quantifying annual mass budgets or analyzing interannual changes in ice velocity requires knowing when and where observations of glacier velocity could be aliased by subannual variability. Here, we analyze 16 years of velocity data for Totten Ice Shelf, which we generate at subannual resolution by applying feature-tracking algorithms to several hundred satellite image pairs. We identify a seasonal cycle characterized by a spring to autumn speedup of more than 100 m yr −1 close to the ice front. The amplitude of the seasonal cycle diminishes with distance from the open ocean, suggesting the presence of a resistive back stress at the ice front that is strongest in winter. Springtime acceleration precedes summer surface melt and is not attributable to thinning from basal melt. We attribute the onset of ice shelf acceleration each spring to the loss of buttressing from the breakup of seasonal landfast sea ice.
The Journal of the Acoustical Society of America, 2009
ABSTRACT Acoustic resonances are exploited in many natural and human‐made systems, and demonstrat... more ABSTRACT Acoustic resonances are exploited in many natural and human‐made systems, and demonstrations of the phenomena have been presented previously [Greene et al., J. Acoust. Soc. Am. 124, 2568 (2008); Argo IV et al., J. Acoust. Soc. Am. 125, 2625 (2009)]. In practice, resonance is always accompanied by energy loss, which limits the maximum excursion of a system. When sufficiently large, this loss can alter the resonance frequency of the system. An air bubble in water is an example of a lossy acoustic resonator and is well‐suited for demonstrating acoustic damping in the Listen Up paradigm. For the proposed demonstration, students will observe the resonance of a water‐filled drinking glass by striking it with a metal spoon to produce a strong ringing sound. They will then introduce damping into the system by using a stream of water to entrain bubbles which will deaden the ringing response of the system. The primary mechanism for the acoustic energy dissipation is conversion into heat during bubble oscillation. An explanation of this process is presented with a detailed description of the proposed experiment.
The Journal of the Acoustical Society of America, 2009
ABSTRACT One goal of Project Listen Up is to enhance children's understanding of acoustic... more ABSTRACT One goal of Project Listen Up is to enhance children's understanding of acoustics through engagement in basic acoustics experiments. This work proposes an experiment that examines the resonant frequencies of an air column. Equipment for this experiment consists of a small tunable oscillator circuit connected to a loudspeaker, which can also be used for other experiments in the kit. The experimenter will provide a cardboard tube, rubber band, plastic wrap, and sand. Resonance is demonstrated by placing the loudspeaker at the base of the tube, covering the top of the tube with a plastic wrap membrane, and placing sand grains on top of the membrane. As frequency is adjusted, the sand grains are excited at the resonance frequencies of the tube. Frequencies at which sand motion is observed can be compared to a simple algebraic model, which relates the length of the tube to the resonance frequencies of the system. An optional advanced experimental track investigates the effect of varying the length of the tube. This experiment develops intuition for the relationship between frequency and wavelength and builds understanding of resonant systems.
The Journal of the Acoustical Society of America, 2008
ABSTRACT The Listen Up project seeks to develop an educational booklet and apparatus that will be... more ABSTRACT The Listen Up project seeks to develop an educational booklet and apparatus that will be used to foster interest in acoustics and teach basic acoustical concepts to middle school students. The packaged kit must be low cost; hence this experiment uses a 16 oz plastic water bottle as a Helmholtz resonator, a disposable syringe, and an inexpensive pitch pipe. Understanding the Helmholtz resonator is fundamental to many applications in acoustics. A simple algebraic model of the device, derived from a mechanical mass-spring analogy, relates the volume of air in the bottle to the resonance frequency of the system, and hence the pitch that is produced when one blows over the bottle opening. The volume of air inside the bottle can be easily and accurately controlled by adding water with a graduated syringe. The dependence of pitch on the volume of air in the bottle can be systematically demonstrated, and the validity of the model can be checked by comparing the sound produced to musical notes from the pitch pipe. This experiment yields a physical understanding of a common acoustical phenomenon and inspires further interest and study of more complex phenomena.
The Journal of the Acoustical Society of America, 2011
ABSTRACT The unique molecular structures of gas hydrates result in curious acoustic properties, w... more ABSTRACT The unique molecular structures of gas hydrates result in curious acoustic properties, which have yet to be adequately described. Understanding the acoustic behavior of stable and dissociating gas hydrates in liquids is vital for their localization and quantification using seismic or echosounding techniques. Further, with improved characterization of the acoustic properties of gas hydrates and bubbly liquids containing methane gas, acoustic methods may become an invaluable tool for monitoring hydrate dissociation and determining the magnitude of its effects on climate change. Acoustic properties of gassy substances are known to have a strong dependence on excitation frequency; however, tabulated values of hydrate material properties are most often measured in the frequency range of hundreds of kilohertz, while natural hydrate deposits and gas seeps are typically surveyed at seismic frequencies several orders of magnitude below laboratory measurement frequencies. This presentation details laboratory experiments in which a low-frequency (10 Hz to 10 kHz) acoustic resonator apparatus was used to measure (a) sound speeds of bubbly liquids containing ideal and real gases and (b) bulk moduli and dissociation pressures of natural structure I and structure II gas hydrate samples. [Work supported by the Office of Naval Research.]
The Journal of the Acoustical Society of America, 2010
ABSTRACT Cold seeps are gas vents that are found in the ocean, often along continental shelves ne... more ABSTRACT Cold seeps are gas vents that are found in the ocean, often along continental shelves near sediment-borne methane hydrates. Methane hydrates and methane gas seeps are of particular interest both for their potential use as an energy source and for their possible contribution to global climate change. This work is an initial step toward passively locating cold seeps and quantifying their gas flow rates using acoustic remote sensing techniques. Results are presented from laboratory experiments in which gas fluxes were determined from the radiated acoustic signature of a model seep. The physical principle that supports the technique and its accuracy will be discussed. [Work supported by ONR.].
The Journal of the Acoustical Society of America, 2009
ABSTRACT Methane hydrates occur naturally on the ocean bottom and in the upper layers of sediment... more ABSTRACT Methane hydrates occur naturally on the ocean bottom and in the upper layers of sediment on continental shelves. Seismic surveying could be used to locate methane hydrates; however, their low‐frequency acoustic properties are not well‐known. In addition, these properties can vary dramatically depending on whether the methane is in a gas or solid phase. As a step toward better understanding the three‐phase case of gassy sediments in water, the two‐phase case of methane gas bubbles in water was investigated. Wood’s equation is often used to model sound propagation in bubbly liquids and has been widely verified by experiments at atmospheric pressure. However, there is little information in the literature verifying the validity of Wood’s equation at high pressures. Low‐frequency (0.5–10‐kHz), resonator‐based sound speedmeasurements were obtained for air bubbles in water and methane bubbles in water under pressures ranging from 1 to 10 atm at room temperature. The results are presented and compared to the predictions of Wood’s equation. [Work sponsored by ONR.]
The Journal of the Acoustical Society of America, 2010
ABSTRACT The didgeridoo is an ancient Aboriginal instrument traditionally crafted from Eucalyptus... more ABSTRACT The didgeridoo is an ancient Aboriginal instrument traditionally crafted from Eucalyptus trees which have been hollowed out by termites. The instrument is an excellent example of a simple one-dimensional acoustic resonator with a fundamental resonance corresponding to one-half wavelength. Today, the ubiquity and low cost of PVC pipes make didgeridoos inexpensive, easy to find, and trivial to construct from materials found at any hardware store. Students will have fun learning to make sounds with the instrument-perhaps they will even learn the technique of circular breathing-all while exploring fundamental principles of acoustics. As further investigation students can hum as they play, resulting in "beats, the speed of which can be adjusted by changing the pitch of the hum.
We present the Antarctic Mapping Tools package, an open-source MATLAB toolbox for analysis and pl... more We present the Antarctic Mapping Tools package, an open-source MATLAB toolbox for analysis and plotting of Antarctic geospatial datasets. This toolbox is designed to streamline scientific workflow and maximize repeatability through functions which allow fully scripted data analysis and mapping. Data access is facilitated by several dataset-specific plugins which are freely available online. An open architecture has been chosen to encourage users to develop and share plugins for future Antarctic geospatial datasets. This toolbox includes functions for coordinate transformations, flight line or ship track analysis, and data mapping in georeferenced or projected coordinates. Each function is thoroughly documented with clear descriptions of function syntax alongside examples of data analysis or display using Antarctic geospatial data. The Antarctic Mapping Tools package is designed for ease of use and allows users to perform each step of data processing including raw data import, data analysis, and creation of publication-quality maps, wholly within the numerical environment of MATLAB.
Data graphics shape the way science is communicated, and the color schemes we employ can either... more Data graphics shape the way science is communicated, and the color schemes we employ can either faithfully represent or tacitly obscure the data a figure is intended to convey (Tufte, 1983). Tasteful use of color can make data graphics visually appealing and can draw viewers in, engaging the audience and encouraging further inspection of a figure. But wherever color is used to represent numerical values, its role transitions from a mere aesthetic nicety to carrying the responsibility of conveying data honestly and accurately. Yet, biases introduced by some common colormaps have gone widely unrecognized within the oceanographic community. Here, we describe the pitfalls of some commonly used colormaps, provide guidelines on effective, accurate colormap selection, and present a suite of perceptually uniform cmocean colormaps that have been designed for oceanographic data display. The cmocean package is available across multiple software programs, including MATLAB, Python, R, Generic Mapping Tools, and Ocean Data Viewer.
Passive acoustic techniques are of interest as a low-power means of quantifying underwater point-... more Passive acoustic techniques are of interest as a low-power means of quantifying underwater point-source gas ebullition. Toward the development of systems for logging natural seep activity, laboratory experiments were performed that exploited the bubble's Minnaert natural frequency for the measurement of gas flow from a model seep. Results show agreement among acoustic, optical, and gas trap ebullition measurements over the range of emission rates from 0 to 10 bubbles per second. A mathematical model is proposed to account for the real gas behavior of bubbles which cannot be approximated as ideal, such as methane at marine depths exceeding 30 m.
Methane hydrates are naturally-occurring ice-like substances found in
permafrost and in ocean sed... more Methane hydrates are naturally-occurring ice-like substances found in permafrost and in ocean sediments along continental shelves. These compounds are often the source of cold seeps|plumes which vent methane into aquatic environments, and may subsequently release the potent greenhouse gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates through the use of seismic surveys and echo-sounding technology, this work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of methane gas bubbles and methane hydrates in water under simulated ocean-floor conditions of low temperatures and high pressures. Products of the experiments and analysis presented in this thesis include (a) passive acoustic techniques for measurement of gas flux from underwater seeps, (b) a modified form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates. Experimental procedures and results are presented, along with analytical and numerical models which support the findings.
Problem The high precision of laser altimetry cannot be fully exploited for time series analysis ... more Problem The high precision of laser altimetry cannot be fully exploited for time series analysis on floating ice because surface feature advection aliases Eulerian repeat measurements.
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permafrost and in ocean sediments along continental shelves. These compounds
are often the source of cold seeps|plumes which vent methane into
aquatic environments, and may subsequently release the potent greenhouse
gas into the atmosphere. Methane hydrates and methane gas seeps are of
particular interest both for their potential as an energy source and for their
possible contribution to climate change. In an effort to improve location of
hydrates through the use of seismic surveys and echo-sounding technology, this
work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior
of methane gas bubbles and methane hydrates in water under simulated
ocean-floor conditions of low temperatures and high pressures. Products of the
experiments and analysis presented in this thesis include (a) passive acoustic
techniques for measurement of gas flux from underwater seeps, (b) a modified
form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates.
Experimental procedures and results are presented, along with analytical and
numerical models which support the findings.