Detection of buried targets using a synthetic aperture sonar   总被引：1，自引：0，他引：1  

Piper  J.E. Commander  K.W. Thorsos  E.I. Williams  K.L. 《Oceanic Engineering, IEEE Journal of》2002,27(3):495-504

This paper presents observations of buried target detections made using a 20-kHz synthetic aperture sonar. At grazing angles below the critical angle, surprisingly high signal-to-noise detections were made of cylindrical targets buried at depths of 15 and 50 cm. During a separate set of measurements, buried spheres were clearly seen at steep grazing angles, but were generally not seen below the critical angle. Since scattering from wave-generated sand ripples may contribute to detections at grazing angles below critical angle, the information available on the ripple fields is discussed and used in acoustic backscatter simulations for the buried spheres. Lack of information on the ripple height precludes a definitive explanation for the absence of buried sphere detections at subcritical grazing angles.  相似文献   

Industry participation in stock assessment: the New Zealand SNA1 snapper (Pagrus auratus) fishery     

Mark N. Maunder  Paul J. Starr   《Marine Policy》2002,26(6)

We describe industry funded contributions to the assessment of the SNA1 snapper (Pagrus auratus) fishery during the 1990s and discuss the advantages and disadvantages of industry funded research. We also provide background on the history of fisheries management in New Zealand, on the current assessment and management processes, and on the SNA1 snapper fishery. In the SNA1 fishery, the contributions of industry and the cooperation with Government scientists has resulted in high quality assessments. In our opinion, the advantages of industry funded research out weigh the disadvantages and suggest that industry funded assessments are highly desirable and should be an integral part of any management system.  相似文献   

Significance of pteropods in deciphering the late Quaternary sea-level history along the southwestern Indian shelf     

A. Singh  K. Ramachandran  M. Samsuddin  N. Nisha  V. Haneeshkumar 《Geo-Marine Letters》2001,20(4):243-252

The paper evaluates the usefulness of pteropods in palaeobathymetric synthesis along the southwestern continental shelf of India. Core samples collected from the shelf off north Kerala (SW coast of India) were studied for faunal assemblages (pteropods and foraminifers), calcium carbonate contents and lithological characteristics. A fundamental precept for considering any organism as a bathometer is that it should be highly sensitive to changing water depths. To ascertain this, the bathymetric distribution patterns of modern pteropods as well as planktonic and benthic foraminifers were recorded in core-top samples. The results reveal that certain pteropod species (Limacina inflata, Creseis acicula, Creseis virgula, and Creseis chierchiae) are highly depth sensitive. The response of these species to depth changes was assessed in terms of the L. inflata and Creseis spp. abundance ratio. A model for the relationship between water depths and the L. inflata/Creseis spp. ratio is proposed for the southwestern shelf of India. Variations of benthic/planktonic foraminifers (BF/PF) and pteropods/planktonic foraminifers (Pt/PF) in the modern sediments were also found to be depth controlled. Two sediment cores, representing the last 36,000 and 23,000 years, were collected to investigate past sea-level changes. These cores comprised two distinct lithological units, the upper unit corresponding to the Holocene, and the lower unit to the last glacial period. The L. inflata/Creseis spp. model was successfully applied to the fossil record for reconstructing the palaeobathymetry of the shelf study locations. Down-core variations in the BF/PF and Pt/PF ratios support these inferred sea-level changes. Major periods of sea-level oscillations were also found to have a strong influence on the calcium carbonate distribution. For both core sites, the palaeobathymetric curves reflect consistency in terms of changing sea level. The results suggest that the sea level stood around 100 m below the present mean sea level during the last glacial maximum. A rapid rise in sea level was documented between 15 and 10 ka B.P. The sea-level rise has been slower since 7 ka B.P.  相似文献   

Comments on free and damped vibrations of an orthotrophic rectangular plate with one edge free while the rest are elastically restrained against rotation by M. Barbaros Okan     

P. A. A. Laura  R. O. Grossi  L. Ercoli 《Ocean Engineering》1983,10(2):139

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Selection of Cape Hake (Merluccius Merluccius Capensis Castelnau And Merluccius Merluccius Paradoxus Franca) by Bottom-Trawl Cod-Ends     

Bohl  H.; Botha  L.; van Eck  T. H. 《ICES Journal of Marine Science》1971,33(3):438-471

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Solitary wave forces on horizontal cylinders     

P. Sibley  L.E. Coates  K. Arumugam 《Applied Ocean Research》1982,4(2):113-117

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Particle transport from the West African shelves of Liberia and Sierra Leone to the deep sea: A chemical approach     

Donald W. Eggimann  Peter R. Betzer  Kendall L. Carder 《Marine Chemistry》1980,9(4):283-306

The chemical and mineralogical composition of suspended particle suites has been used to assess off-shelf transport on the West African shelves of Liberia and Sierra Leone. Using the ratios of Si/Al, Fe/Al, Mg/Al and Mn/Al as tracers, it was possible to detect shelf-derived materials in slope waters. In the majority of cases, these inputs could not have been detected using particle mass or light scattering measurements and could only be measured by using the chemical signatures of the particulate matter. At the time of sampling, the suspensate which had been moved seaward over the slope was detected adjacent to submarine canyons and highly turbid areas on the outer shelf. The chemical and mineralogical composition of the suspensates, and sediments in the adjacent eastern Atlantic basin are similar to those found in the water column seaward of the West African continental shelves and yet distinct from the Sahelian dust which is considered the major source of sedimentary material for the tropical and semi-tropical areas of the deep eastern basin. These findings suggest that materials from this shelf area could be a more important input to the deep sea than was previously realised.  相似文献   

The biochemical composition of the cypris larva of the barnacle Balanus balanoides L     

Holland  D. L.; Walker  G. 《ICES Journal of Marine Science》1975,36(2):162-165

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Physical oceanography   总被引：2，自引：0，他引：2  

K. Yoshida  K. Takano  T. Teramoto  Y. Toba  Y. Nagata  K. Kajiura  T. Nan'nichi  N. Iwata  T. Takahashi  M. Chaen  T. Tabata 《Journal of Oceanography》1971,27(6):248-264

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Beach accretion and erosion, Burullus-Gamasa coast, Egypt     

Y.M. Anwar  A.R. Gindy  M.A. El Askary  N.M. El Fishawi 《Marine Geology》1979,30(3-4):M1-M7

Several areas of erosion and accretion were observed along the Burullus-Gamasa beach. The accreted sands are coarser and less sorted than the eroded ones. Differentiation between them could be achieved on the basis of their grain-size fractions, shape of grain-size distribution curves and statistical grain-size parameter relationships.  相似文献