TWO MODELING APPROACHES FOR REVERBERATION IN A SHALLOW WATER WAVEGUIDE WHERE THE SCATTERING ARISES FROM A SUB-BOTTOM INTERFACE

2009 ◽  
Vol 17 (01) ◽  
pp. 29-43 ◽  
Author(s):  
CHARLES W. HOLLAND ◽  
DALE D. ELLIS
Keyword(s):  
Shallow Water ◽  
Silty Clay ◽  
Sediment Layer ◽  
Angle Distribution ◽  
Vertical Angle ◽  
Fine Grained ◽  
Bottom Interface ◽  
Grazing Angles ◽  
Scattering Kernel ◽  
Sediment Interface

In shallow water environments where the uppermost sediment layer is a fine-grained fabric (e.g. clay or silty-clay), the observed reverberation may be dominated by scattering from the sub-bottom. Here, reverberation predictions from normal mode and energy flux models are compared for the case where the scattering arises from a sub-bottom half-space under a fine-grained sediment layer. It is shown that in such an environment, the position of the angle of intromission, in addition to the angular dependence of the scattering kernel, is a factor controlling the reverberation and its vertical angle distribution. It is also shown that the reverberation from a sub-bottom horizon is typically governed by higher grazing angles than the case where the scattering occurs at the water–sediment interface. There was generally very close agreement between the models as a function of frequency (200–1600 Hz), layer thickness (0–8 m), and range (1–15 km). The model comparisons, showing some differences, illuminate the result of different approximations in the two approaches.

Surficial Sediments of Lake Erie

1976 ◽  
Vol 33 (3) ◽  
pp. 385-403 ◽  
Author(s):  
R. L. Thomas ◽  
J.-M. Jaquet ◽  
A. L. W. Kemp ◽  
C. F. M. Lewis
Keyword(s):  
Grain Size ◽  
Shallow Water ◽  
Lake Erie ◽  
Central Basin ◽  
Sediment Accretion ◽  
Western Basin ◽  
Grab Sampling ◽  
Fine Grained ◽  
Basin Region ◽  
Skewness And Kurtosis

On the basis of extensive echosounding and grab sampling, three major units have been recognized in Lake Erie: till and bedrock, glaciolacustrine clay, and postglacial muds. These units represent the late glacial and postglacial evolution of the basin and occur in an offshore younging sequence. The main basin of the lake is subdivided by residual glacial moraines into four depositional basins: Western, Sandusky, Central, and Eastern basins. The sediment texture has been defined by moment measures (mean, standard deviation, skewness, and kurtosis), the trends of which are related to the mixing of two primary grain-size populations in the sand- and clay-size ranges. A third grain-size mode in the silt size, composed of fine quartz with some carbonate, has been recognized. This mode has a modifying effect on the symmetry of the two primary populations and may, to some extent, be sufficiently abundant to behave as a discrete population. The trends in the textural characteristics, particularly skewness and kurtosis, have been utilized to define energy regimes at the sediment–water interface which indicates three distinct sedimentary or hydraulic regions: 1) Western basin region — Fine-grained sediment accretion in shallow water related to an imbalance in sediment budget, with high input loadings of fine-grained sediment, and deficit in coarse materials, with an excess of input over sediment export to the Central basin region. This results in net sediment accretion in shallow water with texture in disequilibrium with environmental energy, which produces mixing and suspension, followed by redeposition; 2) Central basin region — West to East coarsening of sediment in textural equilibrium with hydraulic energy, as it relates to increasing fetch under westerly and southwesterly prevailing winds; 3) Eastern basin region — Deepwater basin with sediments showing decreasing size offshore with increasing water depth. The deepwater sediment is modified by the influx of substantial quantities of the silt-size material derived from shoreline erosion in the north shore of the Central basin region.The interrelationships of parameters indicate textural dependence on mineralogic composition, particularly important being the relationship of clay concentration to mean grain size. This has particular value in modelling the physical behavior of clay-associated geochemical elements such as phosphorus.

RECONSTRUCTION OF LAYERED ELASTIC BOTTOM CHARACTERISTICS BY THE FREQUENCY DEPENDENCE OF SOUND REFLECTIVITY

2001 ◽  
Vol 09 (04) ◽  
pp. 1475-1484 ◽  
Author(s):  
VLADIMIR N. FOKIN ◽  
MARGARETE S. FOKINA
Keyword(s):  
Frequency Dependence ◽  
Half Space ◽  
Simulated Data ◽  
Elastic Half Space ◽  
Ocean Bottom ◽  
Sediment Layer ◽  
Elastic Bottom ◽  
Sea Bottom ◽  
Sound Reflection ◽  
Grazing Angles

The relation between the sound reflection losses measured at fixed grazing angles and the characteristics of the sediment layer and underlying half-space is considered. Based on this relation, a method of the reconstruction of the sea bottom characteristics is developed for a ocean bottom consisting of a single sediment layer overlaying a semi-infinite elastic half-space. Using this bottom model, the reconstruction of the characteristics of a layered elastic bottom is performed from the numerically simulated data with induced synthetic error.

scholarly journals Water flow through sediments and at the ice-sediment interface beneath Sermeq Kujalleq (Store Glacier), Greenland

2021 ◽  
pp. 1-20
Author(s):  
Samuel H. Doyle ◽  
Bryn Hubbard ◽  
Poul Christoffersen ◽  
Robert Law ◽  
Duncan R. Hewitt ◽  
...  
Keyword(s):  
Water Pressure ◽  
Pressure Rise ◽  
Stress Transfer ◽  
Flexural Wave ◽  
Sediment Layer ◽  
Progressive Decrease ◽  
Large Pressure ◽  
Gap Opening ◽  
Flow Through ◽  
Sediment Interface

Abstract Subglacial hydrology modulates basal motion but remains poorly constrained, particularly for soft-bedded Greenlandic outlet glaciers. Here, we report detailed measurements of the response of subglacial water pressure to the connection and drainage of adjacent water-filled boreholes drilled through kilometre-thick ice on Sermeq Kujalleq (Store Glacier). These measurements provide evidence for gap opening at the ice-sediment interface, Darcian flow through the sediment layer, and the forcing of water pressure in hydraulically-isolated cavities by stress transfer. We observed a small pressure drop followed by a large pressure rise in response to the connection of an adjacent borehole, consistent with the propagation of a flexural wave within the ice and underlying deformable sediment. We interpret the delayed pressure rise as evidence of no pre-existing conduit and the progressive decrease in hydraulic transmissivity as the closure of a narrow (< 1.5 mm) gap opened at the ice-sediment interface, and a reversion to Darcian flow through the sediment layer with a hydraulic conductivity of ≤ 10−6 m s−1. We suggest that gap opening at the ice-sediment interface deserves further attention as it will occur naturally in response to the rapid pressurisation of water at the bed.

scholarly journals Distribution of Arsenic with Iron, Manganese and Copper in Borehole Sediments of the River Tista and Jamuna

2013 ◽  
Vol 61 (2) ◽  
pp. 207-210 ◽  
Author(s):  
Mohammad Arifur Rahman ◽  
Md Jahangir Alam ◽  
Nur-E-Alam Siddique ◽  
AM Shafiqul Alam
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Chemical Analysis ◽  
Arsenic Concentration ◽  
Sediment Layer ◽  
Fine Grained ◽  
Lower Depth ◽  
Iron Manganese ◽  
Clay Type

Boreholes sediments (1-6 m depth) of the river Tista and Jamuna in Bangladesh were collected for the analysis of As, Fe, Mn, Cu and organic carbon. Chemical analysis reveals that Mn and Fe hydroxides and organic matter are the major leachable solids which carrying As. High levels of arsenic concentration in aquifers are associated with fine grained sediments at the lower depth of the sediment layer. The highest As containing sediment was gray and texture of sediment was clay type. The colour of the least As containing sediment was white and texture of sediment was sandy. In addition, this study indicate that As is closely associated with Fe and slightly correlated with Mn and Cu in the sediment of the river Tista and Jamuna. Arsenic was distributed regularly DOI: http://dx.doi.org/10.3329/dujs.v61i2.17072 Dhaka Univ. J. Sci. 61(2): 207-210, 2013 (July)

PETROLEUM PROSPECTS, BLIGH WATER, FIJI

1972 ◽  
Vol 12 (1) ◽  
pp. 62
Author(s):  
A.W. Lindner
Keyword(s):  
Shallow Water ◽  
Sedimentary Rocks ◽  
Petroleum Exploration ◽  
Seismic Profiles ◽  
Fine Grained ◽  
Porosity And Permeability ◽  
Oil Seepage ◽  
The Government ◽  
Basement High ◽  
Offshore Petroleum

The Fiji Archipelago constitutes a segment of the island arc system of the southwest Pacific. The islands in the group comprise a mixture of igneous and sedimentary rocks including carbonates. The hydrocarbon potential of the region has been emphasised since the Tonga oil seepage drew the attention of the oil industry to this part of the globe in 1968.Southern Pacific Petroleum (Fiji) Limited was granted the first offshore petroleum concession in Fiji by the Government in 1969 and the negotiation for the concession resulted in the formulation of Fijian offshore petroleum exploration legislation. Reconnaissance sparker seismic shooting indicated the existence of stratified rocks beneath Bligh Water and subsequent aeromagnetics and multiple coverage seismic has confirmed the presence of a sedimentary basin.The oldest dated sedimentary rocks in Fiji are Eocene. They form part of a very thick sequence, including volcanics, ranging into Lower Miocene which regionally has been mildly metamorphosed. Locally this sequence has been intruded by intermediate to basic plutonic stocks which subsequently have been unroofed by widespread intra-Miocene erosion. This sequence constitutes the economic basement in the region. Middle to Upper Miocene and Pliocene clastic, marine, fossiliferous sediments and shallow water carbonates on the two main islands of Fiji were deposited in localised basins, generally in complex association with volcanic rocks.The sedimentary column contains considerable fine grained, dark coloured, marine elastics. Bioclastic limestone, also present in the sequence, has excellent porosity and permeability. Good reservoir character is similarly indicated for some of the coarser elastics, despite the lack of quartz.The seismic data, when integrated with the geology of the islands, infer that the deepest continuous reflection horizon represents the intra-Miocene unconformity; additionally, the data show that the Bligh Water Basin is divided into northern and southern components, divided by a basement high. The southern region appears more attractive for exploration as 7000 ft. (2100 m.) of section is indicated and the area is covered by shallow water. Faulting and drape features are the obvious structural forms present. Several discontinuous reflection events, commonly occurring at equivalent positions on different seismic profiles, may indicate presence of carbonate banks or cays similar to the type of carbonate deposits exposed in the succession onshore.

Distribution of metals in sediments of the elbe estuary in 1994

1998 ◽  
Vol 37 (6-7) ◽  
pp. 109-116 ◽  
Author(s):  
Alexander Groengroeft ◽  
Ursula Jaehnig ◽  
Guenter Miehlich ◽  
Rolf Lueschow ◽  
Vera Maass ◽  
...  
Keyword(s):  
Grain Size ◽  
Size Fraction ◽  
Outer Part ◽  
Quality Criteria ◽  
Total Sample ◽  
Enrichment Factors ◽  
Contamination Level ◽  
Sediment Layer ◽  
Elbe Estuary ◽  
Fine Grained

In 1994 the quality of the uppermost sediment layer of the Elbe estuary was surveyed for various planning purposes. For example, metal contents were determined in the grain-size fraction &lt;20 μm, and the concentrations of PAH were analyzed in the total sample, with correcting for grain-size effect being done numerically. Using the specific zinc contents in fine-grained particles, transport phenomena were recognized: particles of marine origin are transported &gt;100 km upstream to the Hamburg area, causing contamination to decrease to about 50% of the fluvial level. The local metal contamination however varies strongly. Samples with low concentration could be detected as geogen; the samples with the highest level of contamination were assumed to have originated from periods of higher river pollution. Of the samples, 74% with medium enrichment factors (2 to 8.5 vs. background for Zn) were suspected to reflect the actual contamination level. Compared to previously reported quality criteria, sediment samples from the upper part of the estuary are still highly contaminated. In the outer part of the estuary the quality is better, but because the marine fine-grained particles still have contamination levels to class II-III in the ARGE Elbe classification system, a further reduction of sediment contamination in the whole estuary would be limited to this level.

Evolution of the magnetic hyperfine field profiles in an ion-irradiated Fe60Al40 film measured by nuclear resonant reflectivity

2021 ◽  
Vol 28 (5) ◽  
Author(s):  
Marina Andreeva ◽  
Alevtina Smekhova ◽  
Roman Baulin ◽  
Yurii Repchenko ◽  
Rantej Bali ◽  
...  
Keyword(s):  
Critical Angle ◽  
Depth Distribution ◽  
Magnetic Hyperfine Field ◽  
Resonant Scattering ◽  
Magnetic Hyperfine ◽  
Total External Reflection ◽  
Hyperfine Fields ◽  
Depth Profiles ◽  
Bottom Interface ◽  
Grazing Angles

Nuclear resonant reflectivity (NRR) from an Fe60Al40 film was measured using synchrotron radiation at several grazing angles near the critical angle of total external reflection. Using laterally resolved measurements after irradiation with 20 keV Ne+ ions of gradually varying fluence of 0–3.0 × 1014 ions cm−2, the progressive creation of the ferromagnetic A2 phase with increasing ion fluence was confirmed. The observed depth selectivity of the method has been explained by application of the standing wave approach. From the time spectra of the nuclear resonant scattering in several reflection directions the depth profiles for different hyperfine fields were extracted. The results show that the highest magnetic hyperfine fields (∼18–23 T) are initially created in the central part of the film and partially at the bottom interface with the SiO2 substrate. The evolution of the ferromagnetic onset, commencing at a fixed depth within the film and propagating towards the interfaces, has been directly observed. At higher fluence (3.0 × 1014 ions cm−2) the depth distribution of the ferromagnetic fractions became more homogeneous across the film depth, in accordance with previous results.

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