Estimating acoustic attenuation from a quantitative seismic profiler

Geophysics ◽  
1981 ◽  
Vol 46 (10) ◽  
pp. 1364-1378 ◽  
Author(s):  
Robert C. Tyce
Keyword(s):  
Sediment Type ◽  
Carbonate Sediments ◽  
Seismic Profiles ◽  
Acoustic Attenuation ◽  
Sea Floor ◽  
Sediment Types ◽  
Physical Laboratory ◽  
High Lateral Resolution ◽  
Wide Range ◽  
Depth Of Burial

Recent work has indicated that acoustic attenuation in marine sediments can be estimated from thin wedges of sediment by means of a quantitative seismic profiler. A capability for near‐bottom seismic profiling at 4 kHz has been developed at the Scripps Institution of Oceanography Marine Physical Laboratory and utilized to determine effective attenuation for several areas of the sea floor. As part of the deep‐tow instrumentation system of the Marine Physical Laboratory, this profiler provides very high lateral resolution. Real time computer displays of equivalent plane‐wave pressure and intensity for seismic profiles have been developed as part of this system. These displays are produced on a standard graphic recorder and can be employed directly to determine effective attenuation by plotting displayed equivalent intensity as a function of depth of burial for a reflector covered by a wedge of sediment. For pelagic sediments, values of about 0.25 dB/m at 4 kHz appear to be common. For the Southern California borderland, a wide range of sediment types is observed, with measured values of effective attenuation ranging from 0.21 to 0.63 dB/m. Highly calcareous (85 percent carbonate) sediments of the Carnegie ridge give quite low values, from 0.1 to 0.2 dB/m, with a suggestion of a rapid decrease in attenuation with depth. For nonbiogenous sediments, values of effective attenuation appear useful for predicting other physical properties such as grain size and porosity, as well as general sediment type, from established interrelations.

scholarly journals Large-Scale Mapping and Predictive Modeling of Submerged Aquatic Vegetation in a Shallow Eutrophic Lake

2002 ◽  
Vol 2 ◽  
pp. 949-965 ◽  
Author(s):  
Karl E. Havens ◽  
Matthew C. Harwell ◽  
Mark A. Brady ◽  
Bruce Sharfstein ◽  
Therese L. East ◽  
...  
Keyword(s):  
Large Scale ◽  
Submerged Aquatic Vegetation ◽  
Aquatic Vegetation ◽  
Eutrophic Lake ◽  
Sediment Type ◽  
Gis Technology ◽  
General Utility ◽  
Sediment Types ◽  
Wide Range ◽  
Sampling Program

A spatially intensive sampling program was developed for mapping the submerged aquatic vegetation (SAV) over an area of approximately 20,000 ha in a large, shallow lake in Florida, U.S. The sampling program integrates Geographic Information System (GIS) technology with traditional field sampling of SAV and has the capability of producing robust vegetation maps under a wide range of conditions, including high turbidity, variable depth (0 to 2 m), and variable sediment types. Based on sampling carried out in AugustœSeptember 2000, we measured 1,050 to 4,300 ha of vascular SAV species and approximately 14,000 ha of the macroalga Chara spp. The results were similar to those reported in the early 1990s, when the last large-scale SAV sampling occurred. Occurrence of Chara was strongly associated with peat sediments, and maximal depths of occurrence varied between sediment types (mud, sand, rock, and peat). A simple model of Chara occurrence, based only on water depth, had an accuracy of 55%. It predicted occurrence of Chara over large areas where the plant actually was not found. A model based on sediment type and depth had an accuracy of 75% and produced a spatial map very similar to that based on observations. While this approach needs to be validated with independent data in order to test its general utility, we believe it may have application elsewhere. The simple modeling approach could serve as a coarse-scale tool for evaluating effects of water level management on Chara populations.

scholarly journals Distribution and density of Lutraria rhynchaena Jonas, 1844 relate to sediment while reproduction shows multiple peaks per year in Cat Ba-Ha Long Bay, Vietnam

2020 ◽  
Vol 15 (1) ◽  
pp. 721-734
Author(s):  
Do Manh Hao ◽  
Do Trung Sy ◽  
Dao Thi Anh Tuyet ◽  
Le Minh Hiep ◽  
Nguyen Tien Dat ◽  
...  
Keyword(s):  
Sustainable Management ◽  
Fishery Management ◽  
Scientific Basis ◽  
Sediment Type ◽  
Medium Sand ◽  
Management Measures ◽  
Sediment Types ◽  
Study Results ◽  
Long Bay ◽  
Benthic Substrate

AbstractLutraria rhynchaena Jonas, 1844 is of great commercial interest, but its reserves have dramatically declined over recent decades. Therefore, there is an urgent need of scientific basis to propose effective fishery management measures and improve artificial aquaculture of the clam. In this study, we investigated the distribution and density of L. rhynchaena, sediment characteristics, and established the clam’s reproductive cycle through monthly observations from August 2017 to July 2018. The study results showed that distribution and density of clams are related to sediment types, and the sediment type of medium sand is likely the best benthic substrate for the clams. The spawning of clams occurred throughout the year with three spawning peaks in January, April and September. For the sustainable management of the clam resource in Cat Ba-Ha Long Bay, the fishery authorities can issue a ban on harvest of the clam in spawning peak months in January, April and September.

scholarly journals Response of stream ecosystem function and structure to sediment metal: Context-dependency and variation among endpoints

Elem Sci Anth ◽  
2014 ◽  
Vol 2 ◽  
Author(s):  
David M. Costello ◽  
G. Allen Burton
Keyword(s):  
Dose Response ◽  
Environmental Context ◽  
Context Dependency ◽  
Acid Volatile Sulfide ◽  
Sediment Type ◽  
Organic Carbon Content ◽  
Ecological Context ◽  
Sediment Types ◽  
Sediment Metals ◽  
Sediment Metal

Abstract Physicochemical and ecological attributes of ecosystems (i.e., environmental context) can modify the exposure and effects of metals, which presents a challenge for ecosystem management. Furthermore, the functional and structural attributes of an ecosystem may not respond equally to metals or be uniformly responsive to environmental context. We explored how physicochemical and ecological context modified sediment metal dose-response for a suite of functional and structural measures. Two sediments with high (HB) and low (LB) acid volatile sulfide and organic carbon content (i.e., physicochemical context) were amended with copper and nickel to establish a gradient of treatments from non-toxic to potentially toxic. Sediments were deployed in each of two streams (i.e., ecological context), incubated for four weeks, and measured for sediment microbe, biofilm, and macroinvertebrate dose-response to metal. The dose-response of microbial function was affected by physicochemical context, with cotton decomposition negatively related to sediment metal only on LB sediments. The abundance of invertebrates from the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT) responded negatively to sediment metal only on LB sediments; however, this dose-response was only observed in one stream, likely because of greater abundance of sensitive EPT taxa (i.e., Baetidae and Ephemerellidae). Biofilm structure was negatively affected by sediment metal in only one stream and there was no difference in dose-response between the two sediment types. Biofilm function was affected by sediment type and stream; production by biofilms exposed to HB sediment was negatively related to sediment metal in only one stream. In all, the majority of our endpoints exhibited responses that were modified by environmental context; however, each component of the ecosystem exhibited unique context dependency. For management of sediment metals, an understanding of context dependency is useful for informed decision-making, but the application of simple contextual filters are unlikely to protect all elements of an ecosystem.

Maturation thermique et histoire de l'enfouissement et de la génération des hydrocarbures du bassin de l'archipel de Mingan et de l'île d'Anticosti, Canada

1990 ◽  
Vol 27 (6) ◽  
pp. 731-741 ◽  
Author(s):  
Rudolf Bertrand
Keyword(s):  
Carbonate Platform ◽  
Burial History ◽  
Upper Ordovician ◽  
Southeastern Part ◽  
Middle Ordovician ◽  
Oil Generation ◽  
Wide Range ◽  
History Of ◽  
Anticosti Island ◽  
Depth Of Burial

Carbonate platform sequences of Anticosti Island and the Mingan Archipelago are Early Ordovician to Early Silurian in age. With the exception of the Macasty Formation, the sequences are impoverished in dispersed organic matter, which is chiefly composed of zooclasts. Zooclast reflectances suggest that the Upper Ordovician and Silurian sequences outcropping on Anticosti Island are entirely in the oil window but that the Lower to Middle Ordovician beds of the Mingan Archipelago and their stratigraphic equivalents in the subsurface of most of Anticosti Island belong to the condensate zone. Only the deeper sequences of the southwestern sector of Anticosti Island are in the diagenetic dry-gas zone. The maximum depth of burial of sequences below now-eroded Silurian to Devonian strata increases from 2.3 km on southwestern Anticosti Island to 4.5 km in the Mingan Archipelago. A late upwarp of the Precambrian basement likely allowed deeper erosion of the Paleozoic strata in the vicinity of the Mingan Archipelago than on Anticosti Island. Differential erosion resulted in a southwestern tilting of equal maturation surfaces. The Macasty Formation, the only source rock of the basin (total organic carbon generally > 3.5%, shows a wide range of thermal maturation levels (potential oil window to diagenetic dry gas). It can be inferred from the burial history of Anticosti Island sequences that oil generation began later but continued for a longer period of geologic time in the northeastern part than in the southeastern part of the island. Oil generation was entirely pre-Acadian in the southern and western parts of Anticosti Island, but pre- and post-Acadian in the northern and eastern parts.

Sedimentary provinces, and associated bedforms and benthos on the Scott Reef-Rowley Shoals platform off north-west Australia

1988 ◽  
Vol 39 (2) ◽  
pp. 133 ◽  
Author(s):  
RJ McLoughlin ◽  
TLO Davis ◽  
TJ Ward
Keyword(s):  
Grain Size ◽  
Carbonate Content ◽  
Sediment Type ◽  
Sediment Grain Size ◽  
North West ◽  
Significant Relationships ◽  
Sediment Types ◽  
Sea Bed ◽  
Mean Grain Size ◽  
High Carbonate

The distribution of sediment types on the Scott Reef-Rowley Shoals platform, a marginal plateau adjoining the continental shelf of north-west Australia, has been investigated. Sediments in this region are predominately muds, with a high carbonate content. Sands, which are scarce, are mainly composed of both benthic and pelagic skeletal remains, with any gravel-sized material consisting of relict molluscan debris and, occasionally, relict coralline material. Correlation of sediment type with sea-bed characteristics as determined from photographs of the bottom at the same site showed significant relationships between mean grain size, and degree of sediment rippling and benthic activity. Similar correlations were found for the skewness measure of the analysis of sediment grain-size frequency. It is concluded that sediment type bears strong relationships with benthic activity and bedform morphology. Correlations between sediment provinces and the distribution of Australian scampi (Metanephrops sp.), a relatively new fishery in the region, are discussed.

Conversaziones 1955

1956 ◽  
Vol 12 (1) ◽  
pp. 9-20
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Rotating Disk ◽  
National Physical Laboratory ◽  
Turbulent Fluctuations ◽  
Research Activities ◽  
Physical Laboratory ◽  
Wide Range ◽  
Dimensional Boundary ◽  
Swept Wings

Conversaziones were held on 19 May and 28 June 1955. At the first there were thirty-six exhibits, covering a wide range of research activities. An acoustical demonstration of the instability of the laminar boundary layer on a rotating disk was given by Mr N. Gregory, Mr J. T. Stuart and Mr W. S. Walker, of the Aerodynamics Division, National Physical Laboratory. The rotating disk illustrates a phenomenon which also occurs in the flow over the swept wings of modern aircraft, the instability in the latter case being due to the growth of self-amplifying vortices in the three-dimensional boundary layer over the nose of the wing. By using a stethoscope the vibrations produced by the vortices and by the random turbulent fluctuations at the edge of the disk can clearly be heard.

scholarly journals A reassessment of ‘<i>Globigerina bathoniana</i>’ Pazdrowa, 1969 and the palaeoceanographic significance of Jurassic planktic foraminifera from southern Poland

2012 ◽  
Vol 31 (2) ◽  
pp. 97-109 ◽  
Author(s):  
Malcolm B. Hart ◽  
Wendy Hudson ◽  
Christopher W. Smart ◽  
Jarosław Tyszka
Keyword(s):  
Water Column ◽  
Central Europe ◽  
Middle Jurassic ◽  
The Other ◽  
Carbonate Sediments ◽  
Calcareous Nannofossils ◽  
Planktic Foraminifera ◽  
Geological Record ◽  
Sea Floor ◽  
Southern Poland

Abstract. ‘Globigerina Ooze’, Foraminiferal Ooze or Carbonate Ooze as it is now known, is a widespread and highly characteristic sediment of the modern ocean system. Comparable sediments are much less common in the geological record although, as we describe here, a number of Middle Jurassic carbonate sediments with distinctive assemblages from Central Europe fulfil many of the criteria. One important component of these assemblages in the Middle Jurassic is ‘Globigerina bathoniana’ Pazdrowa, 1969, first described from the Bathonian sediments near Ogrodzieniec (Poland). The generic assignment of this species and other coeval Jurassic taxa is discussed. This species and many of the other early planktic foraminifera evolved in the Aragonite ll Ocean, together with the other two oceanic carbonate producers: the calcareous nannofossils and the calcareous dinoflagellates. The preservation of carbonate sediments with abundant planktic foraminifera on the sea floor indicates that, by the mid-Jurassic, the carbonate/aragonite compensation depths (and associated lysoclines) must have developed in the water column.

scholarly journals VIII. Gaseous combustion at medium pressures. Part I. —Carbon monoxide air explosions in a closed vessel. Part II. —Methane-air explosions in a closed vessel

1926 ◽  
Vol 225 (626-635) ◽  
pp. 331-356 ◽  
Keyword(s):  
Carbon Monoxide ◽  
National Physical Laboratory ◽  
Closed Vessel ◽  
Engineering Research ◽  
The Past ◽  
Physical Laboratory ◽  
Wide Range ◽  
The Subject ◽  
Temperature And Pressure ◽  
Air Explosion

During the past five years a programme of research involving air-fuel explosions in a closed vessel has been in progress at the National Physical Laboratory for the Engineering Research Board of the Department of Scientific and Industrial Research. Among the experimental results obtained, those relating to Carbon Monoxide and Methane were considered likely to be of interest to the Society, and form the subject of the present communication. Of the two investigations described, the first gives experimental data on the respective influences of hydrogen-air and water vapour on a carbon monoxide-air explosion, and the second relates to explosions of methane and air over a comparatively wide range of initial temperature and pressure.

REFLECTION COEFFICIENTS AND BOTTOM LOSSES AT NORMAL INCIDENCE COMPUTED FROM PACIFIC SEDIMENT PROPERTIES

Geophysics ◽  
1970 ◽  
Vol 35 (6) ◽  
pp. 995-1004 ◽  
Author(s):  
Edwin L. Hamilton
Keyword(s):  
Normal Incidence ◽  
Silty Sand ◽  
Reflection Coefficients ◽  
Silty Clay ◽  
Sediment Properties ◽  
Compressional Waves ◽  
Sea Floor ◽  
Sediment Types ◽  
The Pacific ◽  
Clayey Silt

Rayleigh reflection coefficients and bottom losses of compressional waves at normal incidence on the water‐sediment interface are computed with values of density and velocity measured in sea‐floor sediment samples; main sediment types in three major environments of the Pacific and adjacent areas are included. Some typical average computed values of acoustic bottom loss at normal incidence in db are (1) continental shelf: sands, 8; silty sand, 10; sandy silt, 14; silty clay, 16; (2) abyssal plain: clayey silt, 17; silty clay and clay, 21; and (3) abyssal hill: silty clay and clay, 17. Comparisons with actual measurements at sea by several investigators demonstrate the validity of the approach.

scholarly journals Application of Neural Computing Methods for Interpreting Phospholipid Fatty Acid Profiles of Natural Microbial Communities

2000 ◽  
Vol 66 (2) ◽  
pp. 694-699 ◽  
Author(s):  
Peter A. Noble ◽  
Jonas S. Almeida ◽  
Charles R. Lovell
Keyword(s):  
Sensitivity Analysis ◽  
Fatty Acid ◽  
Cross Validation ◽  
Phospholipid Fatty Acid ◽  
Computing Methods ◽  
Sediment Type ◽  
Data Set ◽  
Linear Discriminant ◽  
Sediment Types ◽  
Hidden Neurons

ABSTRACT The microbial community compositions of surface and subsurface marine sediments and sediments lining burrows of marine polychaetes and hemichordates from the North Inlet estuary (near Georgetown, S.C.) were analyzed by comparing ester-linked phospholipid fatty acid (PLFA) profiles with a back-propagating neural network (NN). The NNs were trained to relate PLFA inputs to sediment type outputs (e.g., surface, subsurface, and burrow lining) and worm species (e.g., Notomastus lobatus, Balanoglossus aurantiacus, andBranchyoasychus americana). Sensitivity analysis was used to determine which of the 60 PLFAs significantly contributed to training the NN. The NN architecture was optimized by changing the number of hidden neurons and calculating the cross-validation error between predicted and actual outputs of training and test data. The optimal NN architecture was found to be four hidden neurons with 60-input neurons representing the 60 PLFAs, and four output neurons coding for both sediment types and worm species. Comparison of cross-validation results using NNs and linear discriminant analysis (LDA) revealed that NNs had significantly fewer incorrect classifications (2.7%) than LDA (8.4%). For the NN cross-validation, both sediment type and worm species had 3 incorrect classifications out of 112. For the LDA cross-validation, sediment type and worm species had 7 and 12 incorrect classifications out of 112, respectively. Sensitivity analysis of the trained NNs revealed that 17 fatty acids explained 50% of variability in the data set. These PLFAs were highly different among sediments and burrow types, indicating significant differences in the microbiota.

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