FM slide (chirp) signals: a technique for significantly improving the signal-to-noise performance in hydroacoustic assessment systems

Ehrenberg, John E.; Torkelson, Thomas C.

doi:10.1016/s0165-7836(00)00169-7

Cited by 54 publications

(24 citation statements)

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“…The pulse duration at both frequencies was 5 ms, and the full beamwidths were 38. The pulses transmitted were not gated sine waves at the given frequency, but rather the frequency was slowly increased over a band of 10 kHz surrounding the target frequency, and pulse compression techniques were used to improve the signal-to-noise ratio and range resolution (Ehrenberg and Torkelson 2000). This leads to an effective pulse duration of 180 ms and a vertical resolution in the acoustic data of about 24 cm.…”

Section: Observations Of Acoustic Scattering From Thin Layersmentioning

confidence: 99%

Acoustic Detection of Oceanic Double-Diffusive Convection: A Feasibility Study

Ross

Lavery

2010

Journal of Atmospheric and Oceanic Technology

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The feasibility of using high-frequency acoustic scattering techniques to map the extent and evolution of the diffusive regime of double-diffusive convection in the ocean is explored. A scattering model developed to describe acoustic scattering from double-diffusive interfaces in the laboratory, which accounted for much of the measured scattering in the frequency range from 200 to 600 kHz, is used in conjunction with published in situ observations of diffusive-convection interfaces to make predictions of acoustic scattering from oceanic double-diffusive interfaces. Detectable levels of acoustic scattering are predicted for a range of different locations in the world's oceans. To corroborate these results, thin acoustic layers detected near the western Antarctic Peninsula using a multifrequency acoustic backscattering system are shown to be consistent with scattering from diffusive-convection interfaces.

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Section: Observations Of Acoustic Scattering From Thin Layersmentioning

confidence: 99%

Acoustic Detection of Oceanic Double-Diffusive Convection: A Feasibility Study

Ross

Lavery

2010

Journal of Atmospheric and Oceanic Technology

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“…In the present study, due to the use of a chirp pulse (Ehrenberg and Torkelson, 2000) and to the ability of the BIOMAPER-II to be towed at depths up to 400 m, we were consistently able to sample acoustically to 500 m, often reaching even greater depths. This allowed us to sample to the bottom over much of the survey region.…”

Section: 42b Wintermentioning

confidence: 57%

“…In the present study, due to the use of a chirp pulse (Ehrenberg and Torkelson, 2000) and to the ability of the BIOMAPER-II to be towed at depths up to 300 m, we were consistently able to sample acoustically to 500 m, occasionally reaching as deep as 550 m. Depending on bathymetry, this allowed us to sample all the way to the bottom over much of the continental shelf. In certain portions of the study area, volume backscattering in the deepest portions of the water column increased from fall to winter, suggestive of a downwards movement of zooplankton.…”

Section: 42a Vertical Movementsmentioning

confidence: 68%

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Distribution, patchiness, and behavior of Antarctic zooplankton, assessed using multi-frequency acoustic techniques

Lawson¹

2006

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The physical and biological forces that drive zooplankton distribution and patchiness in an antarctic continental shelf region were examined, with particular emphasis on the Antarctic krill, Euphausia superba. This was accomplished by the application of acoustic, video, and environmental sensors during surveys of the region in and around Marguerite Bay, west of the Antarctic Peninsula, in the falls and winters of 2001 and 2002. An important component of the research involved the development and verification of methods for extracting estimates of ecologically-meaningful quantities from measurements of scattered sound. The distribution of acoustic volume backscattering at the single frequency of 120 kHz was first examined as an index of the overall biomass of zooplankton. Distinct spatial and seasonal patterns were observed that coincided with advective features. Improved parameterization was then achieved for a theoretical model of Antarctic krill target strength, the quantity necessary in scaling measurements of scattered sound to estimates of abundance, through direct measurement of all necessary model parameters for krill sampled in the study region and survey period. Methods were developed for identifying and delineating krill aggregations, allowing the distribution of krill to be distinguished from that of the overall zooplankton community. Additional methods were developed and verified for estimating the length, abundance, and biomass of krill in each acoustically-identified aggregation. These methods were applied to multifrequency acoustic survey data, demonstrating strong seasonal, inter-annual, and spatial variability in the distribution of krill biomass. Highest biomass was consistently associated with regions close to land where temperatures at depth were cool. Finally, the morphology, internal structure, and vertical position of individual krill aggregations were examined. The observed patterns of variability in aggregation characteristics between day and night, regions of high versus low food availability, and in the presence or absence of predators, together reinforced the conclusion that aggregation and diel vertical migration represent strategies to avoid visual predators, while also allowing the krill access to shallowly-distributed food resources. The various findings of this work have important implications to the fields of zooplankton acoustics and Antarctic krill ecology, especially in relation to the interactions of the krill with its predators.

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“…For the 'known' input signal, the matched-filtering method utilized a Matlabcreated digitally coded chirp signal with a centre frequency of 2.4 MHz and bandwidth of 2 MHz (Ruiter, Zapf, Hopp, Dapp, & Gemmeke). It should be noted that a chirp signal was utilized since it inherently has a higher signal-to-noise (SNR) ratio than corresponding frequency components within a conventional Gaussian pulse signal (Ehrenberg & Torkelson, 2000).…”

Section: Techniques For Deriving the Ultrasound Transit Time Spectrummentioning

confidence: 99%

Ultrasound Transit Time Spectroscopy in Complex Media - Applications and Relationship with Phase Interference

Qahtani¹,

Mueed²

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Osteoporosis is a common disease affecting a large proportion of the human population worldwide. It is described as a bone density and structure deterioration leading to a bone fracture risk. The World Health Organisation (WHO) recognises osteoporosis as one of the most health issue since it is asymptomatic. Globally, two third of women and one third of men over 50 years is diagnosed with osteoporosis.One million in Australia alone have osteoporosis and over six million is considered with low bone mass which cost the budget healthcare sector about 2.75 $ billion dollars a year. The expectation rate of population affected by osteoporosis is assumed to significantly increase with continuous increase of aging population. Therefore, an urgent powerful and precise technique for early detection of bone loss is required.There are several techniques in the market available but the Dual Energy Absorptiometry (DXA) is the only one authorised for this regard by the WHO.However, the controversy is that DXA can only measure the bone density but not yet the bone microarchitecture which is an important factor for the assessment of bone.Quantitative ultrasound (QUS), in terms of broadband ultrasound attenuation (BUA) and speed of sound (SOS), is an alternative method that has been investigated by numerous studies confirming that it is a reliable technique for the assessment of bone and predicting fracture risk. Yet, sufficient knowledge about the propagation of ultrasound waves through complex structure such as cancellous bone is not attained which affects the ability of accurate determination of bone mass and structure.A new proposed hypothesis is that phase interference is the leading attenuation mechanism in complex composite such as cancellous bone due to inhomogeneity transit time of the sonic rays. It also proposed that the propagation of ultrasound wave can be approximated as parallel sonic rays; each has a transit time determined by the proportion of bone (solid) and marrow (liquid) it travels through. Thus, a transit time spectrum (TTS) can be defined describing the proportion of sonic rays of the same transit times. Therefore, this thesis will illustrate a development and validation of an ultrasound transit time model of complex structure such as cancellous bone and identify its relation with phase interference. This study will further explore possible ULTRASOUND TRANSIT TIME SPECTROSCOPY IN COMPLEX MEDIA -APPLICATIONS AND RELATIONSHIP WITH PHASE INTERFERENCE IV applications of the TTS to enhance the effectiveness of ultrasound as a reliable assessment tool for bone.In particular, an examination of the phase interference, created by the variation in transit time, being the main attenuation factor in complex structure among other factors for instance absorption and structure-scattering was performed. Amore fundamental concept of phase interference was investigated showing that it has both temporal and spatial phase interference. The temporal phase interference depends on the pulse length and the transit time di...

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FM slide (chirp) signals: a technique for significantly improving the signal-to-noise performance in hydroacoustic assessment systems

Cited by 54 publications

References 1 publication

Acoustic Detection of Oceanic Double-Diffusive Convection: A Feasibility Study

Acoustic Detection of Oceanic Double-Diffusive Convection: A Feasibility Study

Distribution, patchiness, and behavior of Antarctic zooplankton, assessed using multi-frequency acoustic techniques

Ultrasound Transit Time Spectroscopy in Complex Media - Applications and Relationship with Phase Interference

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