Characterization of sound channel axis and depth in the global ocean

2019 ◽  
Vol 145 (3) ◽  
pp. 1804-1805
Author(s):  
Mukunda Acharya ◽  
Likun Zhang
Keyword(s):  
Global Ocean ◽  
Channel Axis ◽  
Sound Channel

EFFECT OF HORIZONTAL INHOMOGENEITY OF THE OCEAN ON INTERFERENCE OF NEAR-AXIAL WAVES IN LONG-RANGE ACOUSTIC PROPAGATION

2006 ◽  
Vol 14 (04) ◽  
pp. 415-443 ◽  
Author(s):  
NATALIE S. GRIGORIEVA ◽  
GREGORY M. FRIDMAN
Keyword(s):  
Integral Representation ◽  
Long Range ◽  
Deterministic Model ◽  
Sound Field ◽  
Acoustic Propagation ◽  
Time Of Arrival ◽  
Channel Axis ◽  
Sound Channel ◽  
Narrow Strip ◽  
Geometrical Acoustics

When the source and receiver are located close to the depth of the waveguide axis, there exist cusped caustics repeatedly along the axis. A description of the propagation of energy along the waveguide axis in terms of geometrical acoustics is not valid in neighborhoods of cusped caustics, because in these neighborhoods the waves associated with individual ray paths interfere with one another. Neighborhoods of interference grow with range, and at long distances they overlap. This results in the formation of a diffractive (as opposed to ray, i.e., geometrical acoustics) component of the field — the axial wave — that propagates along the sound-channel axis. In this paper, the integral representation of the axial wave obtained before for an arbitrary deep-water waveguide in a three-dimensional range-independent medium is generalized to a range-dependent ocean. The integral representation of the axial wave is derived with the use of solutions of the homogeneous Helmholtz equation concentrated near the sound-channel axis and which decrease exponentially outside a narrow strip containing the axis. The observed time-of-arrival patterns from a number of long-range ocean acoustic propagation experiments show early geometrical-like arrivals followed by a crescendo of energy that propagates along the sound-channel axis and is not resolved into individual arrivals. The practical application of the developed analytic expression for the sound field near the axis of an ocean type waveguide is the discrimination of noninterfering (resolved) and interfering (nonresolved) arrivals. In this paper, the axial wave is simulated for a deterministic model of a range-dependent medium, where the range-dependence results for such things as change in geographic location. The model is based on the information about sound-speed profiles as a function of range between the source and receiving array for the AET experiment. The sound source frequency is taken equal to 75Hz. The propagation range is 3250 km.

Analysis of Current Estimation along Sound-Channel Axis in Central Pacific

2007 ◽  
Vol 46 (7B) ◽  
pp. 4998-5003 ◽  
Author(s):  
Hanako Ogasawara ◽  
Toshiaki Nakamura ◽  
Hidetoshi Fujimori ◽  
Koichi Mizutani
Keyword(s):  
Channel Axis ◽  
Central Pacific ◽  
Sound Channel ◽  
Current Estimation

scholarly journals The effects of biogeochemical processes on oceanic conductivity/salinity/density relationships and the characterization of real seawater

2010 ◽  
Vol 7 (2) ◽  
pp. 773-836 ◽  
Author(s):  
R. Pawlowicz ◽  
D. G. Wright ◽  
F. J. Millero
Keyword(s):  
North Atlantic ◽  
Laboratory Experiments ◽  
Added Mass ◽  
Global Ocean ◽  
Biogeochemical Processes ◽  
The North ◽  
Relative Composition ◽  
Mathematical Investigation ◽  
Density Relationship

Abstract. As seawater circulates through the global ocean, its relative composition undergoes small variations. This results in changes to the conductivity/salinity/density relationship, which is currently well-defined only for Standard Seawater obtained from a particular area in the North Atlantic. These changes are investigated here by analysis of laboratory experiments in which salts are added to seawater, by analysis of oceanic observations of density and composition anomalies, and by mathematical investigation using a model relating composition, conductivity, and density of arbitrary seawaters. Mathematical analysis shows that understanding and describing the effect of changes in relative composition on operational estimates of salinity using the Practical Salinity Scale 1978 and on density using an equation of state for Standard Seawater require the use of a number of different salinity variables and a family of haline contraction coefficients. These salinity variables include an absolute salinity SAsoln, a density salinity SAdens, the reference salinity SR, and an added-mass salinity SAadd. In addition, a new salinity variable S∗ is defined, which represents the preformed salinity of a Standard Seawater component to which biogeochemical processes add material. In spite of this complexity, observed correlations between different ocean biogeochemical processes allow the creation of simple formulas that can be used to convert between the different salinity and density measures, allowing for the operational reduction of routine oceanographic observations.

scholarly journals Characterization of Cyanate Metabolism in MarineSynechococcusandProchlorococcusspp.

2010 ◽  
Vol 77 (1) ◽  
pp. 291-301 ◽  
Author(s):  
Nina A. Kamennaya ◽  
Anton F. Post
Keyword(s):  
Nitrogen Metabolism ◽  
Stress Responses ◽  
Global Ocean ◽  
Marine Cyanobacteria ◽  
Genomic Context ◽  
Carbamoyl Phosphate ◽  
Marine Food Webs ◽  
Photosynthetic Organisms ◽  
Marine Food

ABSTRACTCyanobacteria of the generaSynechococcusandProchlorococcusare the most abundant photosynthetic organisms on earth, occupying a key position at the base of marine food webs. ThecynSgene that encodes cyanase was identified among bacterial, fungal, and plant sequences in public databases, and the gene was particularly prevalent among cyanobacteria, including numerousProchlorococcusandSynechococcusstrains. Phylogenetic analysis ofcynSsequences retrieved from the Global Ocean Survey database identified >60% as belonging to unicellular marine cyanobacteria, suggesting an important role for cyanase in their nitrogen metabolism. We demonstrate here that marine cyanobacteria have a functionally active cyanase, the transcriptional regulation of which varies among strains and reflects the genomic context ofcynS. InProchlorococcussp. strain MED4,cynSwas presumably transcribed as part of thecynABDSoperon, implying cyanase involvement in cyanate utilization. InSynechococcussp. strain WH8102, expression was not related to nitrogen stress responses and here cyanase presumably serves in the detoxification of cyanate resulting from intracellular urea and/or carbamoyl phosphate decomposition. Lastly, we report on a cyanase activity encoded bycynH, a novel gene found in marine cyanobacteria only. The presence of dual cyanase genes in the genomes of seven marineSynechococcusstrains and their respective roles in nitrogen metabolism remain to be clarified.

AXIAL WAVE IN LONG-RANGE PROPAGATION IN A RANGE-INDEPENDENT OCEAN

2004 ◽  
Vol 12 (02) ◽  
pp. 127-147 ◽  
Author(s):  
NATALIE S. GRIGORIEVA ◽  
GREGORY M. FRIDMAN
Keyword(s):  
Integral Representation ◽  
Long Range ◽  
Sound Speed ◽  
Parabolic Cylinder ◽  
Time Of Arrival ◽  
Channel Axis ◽  
Sound Channel ◽  
Cyclic Frequency ◽  
Geometrical Acoustics ◽  
Parabolic Cylinder Functions

In many long-range propagation experiments the source and receiver are placed close to the depth of the waveguide (SOFAR) axis to minimize the interaction of the acoustic field with the ocean's surface and bottom. The time-of-arrival patterns of these experiments consist of resolvable, geometrical-like arrivals followed by an axial crescendo of unresolved energy. It is impossible to explain this late-arriving energy using the geometrical acoustics because of the presence of cusp caustics repeatedly along the waveguide axis. The interference of the wave fields corresponding to the rays located in the vicinity of the caustics near the waveguide axis produces a special "axial wave" that propagates along this axis. The purpose of the paper is to obtain the integral representation of the axial wave for an arbitrary deep-water waveguide in a range-independent medium in long-range acoustic propagation in the ocean when the source and receiver are located close to the depth of the sound-channel axis. The integral representation for the axial wave is derived with the use of solutions of the Helmholtz equation concentrated near the sound-channel axis and which decrease exponentially outside a strip containing the axis. These solutions have the form of the exponentials multiplied by parabolic cylinder functions whose arguments are sections of series in powers of ω-1/2, where ω is a cyclic frequency. Numerical results are obtained for the Munk canonical sound-speed profile.

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