Interference fringes on GLORIA side-scan sonar images from the Bering Sea and their implications     

Q. J. Huggett  A. K. Cooper  M. L. Somers  A. R. Stubbs 《Marine Geophysical Researches》1992,14(1):47-63

GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes (constructively or desctructively) with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations (or wiggles) of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea.  相似文献   

Sio Guyot: A complex volcanic edifice in the western Mid-Pacific Mountains   总被引：1，自引：0，他引：1  

Kenji Nemoto  Loren W. Kroenke 《Geo-Marine Letters》1985,5(2):83-89

Sio Guyot, in the westernmost edge of the Mid-Pacific Mountains, is a large, complex volcanic edifice rising to more than 1200 m below sea level. The summit is divided into two flat-topped areas by a WNW-trending sediment-filled trough. Seismic reflection profiles reveal three acoustic units: an upper transparent layer (pelagic cap), a lower opaque layer (reef- and lagoon-derived sediments), and an acoustic (volcanic) basement. Free-air gravity anomalies indicate three eruptive centers or conduits within the main edifice, which apparently was constructed during late Cretaceous time on a broad basement swell or plateau that today is more than 3400 m below sea level (1500 m above regional abyssal depths).  相似文献   

Imagery of the inhomogeneities of currents on the ocean surface state     

V. A. Dulov  V. N. Kudryavtsev 《Physical Oceanography》1990,1(5):325-336

The influence of inhomogeneities of surface currents on the intensity of breaking wind waves is considered and a model for the relation between whitecap contrasts and the tensor of current gradients is developed. The imagery of typical patterns of ocean currents is discussed. The results of field observations supporting this model are given.Translated by Mikhail M. Trufanov.  相似文献   

The Bengal Fan: Some preliminary results from ODP drilling     

Dorrik A. V. Stow  James R. Cochran  ODP Leg Shipboard Scientific Party 《Geo-Marine Letters》1989,9(1):1-10

Three deep holes, with a maximum penetration of 960 m below sea floor, were drilled into the distal Bengal Fan just south of the equator during ODP Leg 116. The entire section recovered is dominated by sandy silt and mud turbidites derived from the Ganges Delta and from the continental margin of the western Bay of Bengal, interbedded with thin pelagic clays and with biogenic turbidites probably from a local sea mount source. The effects of Hi-Malayan uplift, sea level fluctuations, local tectonics, and fan channel/lobe processes have closely interacted to produce the observed sedimentary record of the past 17 million years since the early Miocene.Coauthors include: James R. Cochran, Lamont-Doherty Geological Observatory (Co-chief scientist); Dorrik A. V. Stow, Nottingham University, England (Co-chief scientist); Christian A. Auroux, Texas A & M University, USA (ODP staff scientist); Kazou Amano, Ibaraki University, Japan; Peter S. Balson, British Geological Survey, Keyworth, Notts, England; Jacques Boulegue, Pierre & Marie Curie University, Paris, France; Garrett W. Brass, University of Miami, Florida, USA; Jeffrey Corrigan, University of Texas, Austin, USA; Stefan Gartner, Texas A & M University, USA; Stuart A. Hall, University of Houston, Texas, USA; Silvia Iaccarino, University of Parma, Italy; Toshio Ishizuka, University of Tokyo, Japan; trena Kacmarska, Mount Allison University, New Brunswick, Canada; Heidemarie Kassens, Kiel University, West Germany; Gregory Leger, Dalhousie University, Halifax, Nova Scotia, Canada; Franca Proto Decima, University of Padova, Italy; C. V. Raman, Andhra University, Visakhapatnam, India; William W. Sager, Texas A & M University, USA; Kozo Takahashi, Woods Hole Oceanographic Institution, USA; Thomas Thompson, 580 Euclid Ave, Boulder, Colo, USA; Jean-Jacques Tiercelin, University of Bretagne, Brest, France; Mark Townsend, University of Nottingham, England; Andreas Wetzel, Tubingen University, West Germany; N. P. Wijayananda, National Aquatatic Resource Agency, Colombo, Sri Lanka; and Colin Williams, Lamont-Doherty Geological Observatory.  相似文献   

AN ECOSYSTEM MODEL ANALYSIS OF THE EFFECT OF MINE TAILINGS ON THE EUPHOTIC ZONE OF A PELAGIC ECOSYSTEM   总被引：1，自引：0，他引：1  

T. R. PARSONS  T. A. KESSLER  LI GUANGUO 《海洋学报(英文版)》1986,5(3):425-436

A computer analysis was performed on experimental results obtained when mine tailings were added to seawater. The Mixed Upper-Layer Ecotrophie Simulation (MULES) model was tested by changing the extinction coefficient and the abundance of heterotrophic zooflagellates. Increasing the extinction coefficient resulted in a delay of phytoplankton growth, an increase in zooplankton standing stock and better growth of autotrophic flagellates compared with diatoms. Zooflagellates in the ecosystem influence the growth of zooplankton; secondary production by zooplankton was markedly depressed at low levels of zooflagellates. These results are believed to be of general significance for the diagnosis of suspended sediment effects on planktonic ecosystems.  相似文献   

Sea-structure interaction for tripod-type steel gravity platform     

M. Berta  A. Blandino  D. Marcon  A. Paruzzolo 《Applied Ocean Research》1981,3(3):113-118

The paper deals with a numerical integrated procedure to calculate the effects of the interaction between sea waves and a tripod-type steel gravity platform. The main aspects to be taken into account for a reliable wave loading analysis of such a new type of platform are emphasized. Among them, the field perturbation effect due to the large bodies presence is analysed. Finally, some principal results in terms of structure global loads obtained by the numerical integrated procedure are presented.  相似文献   

Waveform Shaping of Sonar Transducers for Improving the Vertical Resolution in Sub-bottom Sediments Profiling     

P. Cobo  C. Ranz  A. Fernández  M. Cuesta  D.K. Anthony  M. Siguero 《Marine Geophysical Researches》2005,26(2-4):87-95

Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst. However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude, Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated by its application to a sediment wedge model.  相似文献   

Seismic structure and tectonics of the Shackleton Fracture Zone (Drake Passage,Scotia Sea)     

Riccardo?Geletti  Emanuele?LodoloEmail author  Anatoly?A.?Schreider  Alina?Polonia 《Marine Geophysical Researches》2005,26(1):17-28

The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about 8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of Shackleton Fracture Zone development in the general context of the Drake Passage opening.  相似文献   

An application of a Markov-chain model of shore erosion for describing the dynamics of sediment flux     

V. Ostroumov  V. Rachold  A. Vasiliev  V. Sorokovikov 《Geo-Marine Letters》2005,25(2-3):196-203

Acquisition of coastline retreat rate time sequences (RRTS) is an important component of Arctic coastal monitoring. These data can be used not only to estimate sediment input into the sea during a fixed time period, but also to dynamically simulate sediment flux intensity. The RRTS were investigated at the Marre-Sale (Kara Sea) and Malii Chukochii Cape (East Siberian Sea) key sites. Statistical analysis demonstrated that the RRTS possess Markov characteristic. This allowed coastline dynamics to be described using a Markov-chain model. A model is discussed that combines Markov characteristic and information about the composition and structure of the permafrost sediments to describe sediment flux dynamics.  相似文献   

Using ocean ambient noise for array self-localization and self-synchronization   总被引：2，自引：0，他引：2  

Sabra  K.G. Roux  P. Thode  A.M. D'Spain  G.L. Hodgkiss  W.S. Kuperman  W.A. 《Oceanic Engineering, IEEE Journal of》2005,30(2):338-347

Estimates of the travel times between the elements of a bottom hydrophone array can be extracted from the time-averaged ambient noise cross-correlation function (NCF). This is confirmed using 11-min-long data blocks of ambient noise recordings that were collected in May 1995 near the southern California coast at an average depth of 21 m in the 150-700 Hz frequency range. Coherent horizontal wavefronts emerging from the time derivative of the NCF are obtained across the array's aperture and are related to the direct arrival time of the time-domain Green's function (TDGF). These coherent wavefronts are used for array element self-localization (AESL) and array element self-synchronization (AESS). The estimated array element locations are used to beamform on a towed source.  相似文献