Open Sea Conditions Research Articles

On offshore wind energy mapping using satellite SAR

Offshore wind is an attractive energy source due to the potential of very high wind power as a result of relatively low sea surface roughness. Currently wind observations at meteorological masts positioned in the sea or along the coastline are collected for a minimum of one year and then used in atmospheric models at local scales, for example in the Wind Atlas Analysis and Application Program (WASP) and at regional scales, for example in the Karlsruhe Atmospheric Mesoscale Model (KAMM). Satellite synthetic aperture radar (SAR) imagery provides spatial patterns of wind speed, yet only as snapshots of various atmospheric situations. Regardless, SAR wind speed data may offer new possibilities for mapping offshore wind resources. SAR-derived sea wind maps may be estimated from empirical scatterometer algorithms that are valid for open sea conditions. Scatterometer wind retrieval algorithms are based upon statistical analysis of open-sea wind observations; medium-range forecast winds from weather models; and scatterometer data. Conventional scatterometers measure the normalized radar cross-section at several different aspect angles to infer wind speed and direction. Backscatter coefficients are physically related to wind speed through the roughness of the open sea. Sea roughness is generated by wind-wave interactions in the capillary and short gravity wave spectrum and additional parameters in fetch-limited seas may influence sea roughness compared to the open sea. Hence, SAR-derived wind maps may be biased in fetch-limited seas. Because SAR data provides only one backscatter value in each resolution cell, wind direction must be known a priori. A simple comparison of meteorological observations at a Danish offshore site and from an European Remote Sensing (ERS) SAR wind speed map retrieved using the CMOD4 algorithm shows promising results for wind retrieval from SAR images in coastal regions.

Oil Containment by Boom in Waves and Wind. I: Numerical Model

The effectiveness of a boom is associated with the hydrodynamics in the vicinity of the oil slick that it is attempting to contain, especially under open-sea conditions. A comprehensive investigation of oil containment is provided under various current, wave, and wind conditions. In this paper, a local two-phase nonlinear hydrodynamic numerical model is developed to simulate oil containment by a fixed boom under open-sea conditions. The shape of an oil slick is a function of time, and unstable waves may develop along the oil-water interfacial boundary. This paper describes a simulation of the behavior of the oil slick and deals with important interfacial boundary conditions. A nonhydrostatic pressure is introduced to accommodate the complicated local flow near the oil slick and a successive overrelaxation method is used to solve the pressure equation. A comparison is made of the oil slick shape with and without the hydrostatic pressure assumption. Some simple simulations of free-surface elevations under a number of wave conditions are performed to verify the numerical model. The computed results are in general agreement with those obtained from previous experiments.

Video measurements of near‐surface bubble spectra

Large bubbles >300μm radius have been observed at depths of between 10 cm and 1.2 m using a small video camera attached to a surface following float. In salt water, bubble spectra are presented for both limited fetch and open sea conditions and in fresh water for limited fetch conditions. The void fractions and areas of the observed bubbles are calculated. Measurements were made in a limited range of wind conditions (greater than Beaufort force 5) and depths (between 10 cm and 1.2 m). Video records were analyzed by eye which introduced some uncertainty in the measured size and limited the number of sampled bubbles. Bubble populations are represented by power law spectra . Near the surface, 2 < b < 3 on average; the distribution is very patchy: near breaking waves there are relatively more large bubbles: here 1 < b < 2. Away from the surface, 3.5 < b < 5.

Comments on “On the Estimation of Overwater Bowen Ratio from Sea–Air Temperature Difference”*

The Bowen ratio is an important parameter in the study of air‐sea interaction, particularly in the study of moisture convergence. It is the ratio of sensible to latent heat exchange. Recently, Hsu (1998) reported an interesting relationship between the sea‐air temperature difference (Ts 2 Ta) and the overwater Bowen ratio (B), based on thermodynamic considerations. He used the data collected at four stations in the Gulf of Mexico during the period 1993‐97 and proposed a generic relationship of the form b B 5 a(T 2 T ) sa (1) where the values of a and b are estimated from the field experiments. For open sea conditions, the value of a varied from 0.077 to 0.078, b from 0.67 to 0.71, and the correlation coefficient (r) from 0.85 to 0.89. Very similar results were found in a nearshore region (for Grand Isle, Louisiana). The equation with the highest correlation coefficient (r 5 0.85) is given by Hsu (1998) as 0.69 B 5 0.077(T 2 T ). sa (2) Normally, values of B are large for cold air outbreak conditions. Chou and Yeh (1986) observed B to vary between 0.61 and 0.78 over midlatitude coastal water during cold air outbreak events. During Air-Mass Transportation Experiment (14‐28 February 1974), the value of B was about 0.8 over the Yellow Sea. Hsu also reported Bowen ratios that were substantially higher during a cold-air outbreak that resulted in enhanced sensible heat flux over latent heat flux under these conditions. The linear regression given by Hsu (1998) is 0.81 B 5 0.097(T 2 T ). sa (3)

Source level estimation of dolphin communication calls as a potential method for species identification

Research into the acoustic structure of communication calls of different odontocete species has attempted to identify distinctive features that might assist in discrimination of individuals, pods or species. Most studies have concentrated on frequency modulation characteristics, such as the general shape or contour of the call. Although the source level (SPL re: 1 μPa at 1 m) of echolocation signals has been studied and appears to reflect some body size dependency, signal intensities of ‘‘whistles’’ have not been investigated closely. In this study maximum source levels of communication calls were estimated in open sea conditions, using an acoustic multi-path ranging technique. Preliminary results suggest species-specific differences in maxium call intensities that may provide a useful additional cue to acoustically distinguish species in the wild. Data used for spectral and statistical analysis were recorded using a single hydrophone attached to a pelagic trawl fishing in continental shelf waters in the Bay of Biscay. Maximum SPLs of social calls were extracted and distances between hydrophone and vocalizing animals were obtained exploiting information inherent in recorded muli-path signals. Concurrent visual observation provided species identification. Source levels of calls were calculated based on a calibrated reference signal. Methodology and limitations of this technique are discussed.

WAVE AND CURRENT FIELDS AROUND GAPPED SUBMERGED BREAKWATERS

非線形分散波理論にづく数値モデルを用いて, 幅広透過潜堤周辺の波浪場と流速場の変形解析を行った. 平面水槽を用いた透過潜堤の実験を行い, モデルの妥当性を確認した. 数値計算から潜堤を通過する波は, 潜堤の天端及び不連続部背後面において極大値をとることが明らかとなった. また, 流れは天端面端部の周りで増大し, 平均水位の分布がその推進力となっていることが確認された. これらの特性に関して, 潜堤の空隙特性との関係が検討された.

Foraminiferal associations in Wanganui Bight and Queen Charlotte Sound, New Zealand

Eight benthic foraminiferal associations are recognised in Wanganui Bight and Queen Charlotte Sound, New Zealand, based on cluster analysis of census data from 52 sediment samples. Distribution of the four associations in Wanganui Bight correlates with increasing water depth: Elphidium charlottense/Haynesina depressula/ Patellinella inconspicua association (17–27 m); Patellinella inconspicua/ Quinqueloculina suborbicularis association (20–42 m); Cassidulina carinata/Miliolinella subrotundata association (42–66 m); and Cassidulina carinata/Bulimina submarginata (72–109 m). The four associations in Queen Charlotte Sound are: Quinqueloculina seminula/Elphidium advenum/Haynesina depressula in sandy shallows (0.5–7 m); Epistominella vitreal Haynesina depressula in shallows of the outer Sound (4–12 m); Elphidium vellai/Haynesina depressula in the mouth of the Sound (9–25 m); and Nonionella flemingi/ Notorotalia finlayi in a muddy, sheltered basin (25–42 m). The most important physical factors influencing benthic foraminiferal distribution patterns in these two areas appear to be the characteristics of the water (e.g., temperature, turbidity, salinity) and factors that vary with water depth (e.g., wave and current energy, substrate, light penetration, food availability). Species diversity (α, H) and the relative abundance of planktic foraminiferal tests are mostly greater in the open sea conditions of Wanganui Bight than in Queen Charlotte Sound. In Wanganui Bight both generally increase with increasing depth, although there is a local diversity peak at 70–80 m depth.

Cyclic emersion surfaces and channels within Dinantian limestones hosting the giant Navan Zn-Pb deposit, Ireland

Abstract The Carboniferous succession in the Navan Mine area, which lies near the northern margin of the Dublin Basin, rests unconformably on folded Lower Palaeozoic rocks. The informal stratigraphic nomenclature of the mine is used throughout. Sedimentation began in the late Devonian-early Courceyan with Red Beds reflecting deposition in braided streams and alluvial fans. The overlying Laminated Beds consist of shallow-marine barrier sandstones, tidal-flat/lagoonal mudstones, and sabkha evaporites. The Muddy Limestone is a mud-dominated carbonate sequence reflecting deposition in an open clastic-influenced lagoon. The Pale Beds that follow, and on which attention is focused here, contain at least 44 peritidal and shallow-shelf depositional cycles. The overlying Shaley Pale and Argillaceous Bioclastic Limestones reflect deeper water open-sea conditions. This sequence is truncated by a conspicuous erosion surface overlain by Chadian submarine debris-flows and limestone turbidites. The succession reflects a progressive deepening of the waters as subsidence outpaced sediment accumulation, but emersion surfaces capping cycles indicate that neither deposition nor relative sea-level rise were continuous. Cyclicity and emergence are believed to reflect the interaction of regional subsidence, glacio-eustatic sea-level oscillation, and sediment supply. Emersion surfaces occur in the Laminated Beds and throughout the Pale Beds, and include palaeosols, in situ breccias, pinnacled and hummocky surfaces, and karst-modified topography. Deeply incised channels at four intervals point to larger-scale incision. The lithoclast-bearing conglomerates which they contain indicate extensive emergence nearby. The distribution of these features may be related to the margins of outcrops of Old Red Sandstone and Lower Palaeozoic rocks. The Dinantian limestones in this region host several Zn-Pb ore deposits including Europe’s largest at Navan. The results of this study suggest a relationship to the margins of former emergent carbonate terrains.

Radioactivity Monitored From Moored Oceanographic Buoys

Abstract The principles and operation of a gamma radiation sensor mounted on oceanographic buoys are described. the sensor has proved rugged in severe weather conditions and has satisfactory detection limits and accuracy. Continuous monitoring of artificially produced γ-emitters such as 137Cs, 134Cs, 131I, 133I, 132Te, naturally occuring emitters such as 40k and 214Bi in open sea conditions can provide important information in critical situations.

A two-frequency hydroacoustic scatterometer for bubble scattering investigations

High-frequency bubble layer scattering investigations require the measurement of the intensity of backscattered sound and the corresponding depth of the scatterers below the moving surface. Especially at high sea state conditions and high acoustic frequencies, bubbles acoustically mask the surface, i.e., the surface return cannot be detected. However, this environmental condition is the most interesting one in bubble scattering investigations and a reliable method is required to determine the range of the scatterers to the surface displacement. A method for the determination of the vertical profiling of acoustic scattering in the presence of bubbles at high sea state conditions is presented. It is based on the transmission of a low-frequency signal alternately to the high-frequency signal at which the scattering investigations are performed. The only information that is extracted from the low-frequency echo is the onset of the surface return. It is used to compute the true depth of scatterers at the high frequency. Experiments were conducted to determine the optimum low frequency at which the detection of the surface onset in the presence of a high bubble concentration is ensured. A screening ratio is defined to give a measure of the acoustic masking of the sea surface. It is depicted for an extreme wind condition (20 m/s) for the frequency range of 5-25 kHz and as a function of wind speed for 50 kHz measurements. Selected results of subsurface bubble scattering at 50 kHz from experiments under open sea conditions are presented for the wind speed regime from 9 to 22 m/s. Additionally, the two-frequency scatterometer is used to measure sea state characteristics simultaneously to the scattering investigations by remote sensing techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cathodoluminescence of Recent biogenic carbonates: environmental and ontogenetic fingerprint

AbstractCathodoluminescence (CL) examination of Recent biogenic carbonates shows that they are often luminescent regardless of their mineralogical composition (calcite v. aragonite), habitat (marine v. fresh water), way of life (sessile v. vagile) or environment (hyper- v. hyposaline water). Thus, the presence of luminescence in biogenic particles is not a reliable indicator of diagenetic alteration as some authors have suggested. In addition, CL can reveal variations in the mineralogy of shell material (e.g. regenerated calcitic v. primary aragonitic) and can highlight growth-related structures. Manganese (Mn2+) is the most likely activator of this luminescence, and its content in the shells of benthic organisms seems to be linked to growth rate, ontogeny, open sea conditions, bathymetry and salinity. In neritic environments the Mn2+content and the CL of molluscs and foraminifera appear to increase with decreasing salinity. This study indicates that CL may be an important tool for the determination of environmental and ontogenetic parameters in biogenic carbonates in addition to its current use indiagenetic studies.

The application of high-resolution navigation systems to Leslie-DeLury depletion experiments for the measurement of trawl efficiency under open-sea conditions

A high resolution navigation system adapted from the marine survey industry has been used to enable Leslie-DeLury depletion experiments to be conducted in open-sea locations. Research vessel operation to 1 m accuracy using this system has allowed the delineation and repetitive trawling of discrete areas without the aid of marker buoy systems. The results from two depletion experiments have been reported to illustrate the capabilities of the navigation system and demonstrate the use of the Leslie-DeLury technique for estimating capture efficiency for scallops ( Amusium balloti) and western king prawns ( Penaeus latisulcatus). Commercial otter trawl efficiency for the scallops was shown to be consistently high, with approximately 60% of the animals in the path of the net being taken. More variable capture efficiencies, of 15–31% and 50–53%, were recorded for male and female prawns, respectively. The assumptions inherent in the method, particularly in relation to the mobility of the target species, have been listed and their validity considered. A number of potential applications for this combination of navigation technology and depletion methodology are outlined. These include investigations of short term/seasonal changes in vulnerability and changes in mesh selection with size for demersal species with limited mobility.

Coefficients for sea surface wind stress, heat flux, and wind profiles as a function of wind speed and temperature

Surface layer coefficients for wind profiles, wind stress, and heat flux in typical open sea conditions are briefly reviewed. Businger‐Dyer flux‐gradient relationships and a Charnock wind stress formula fit the empirical data and are dimensionally consistent. These have been solved by an iterative method, and the results are presented in a tabular form suitable for climatological calculations from marine wind and temperature data.

Harbor Oscillations Induced by Nonlinear Transient Long Waves

The process of the excitation of harbors and bays by transient nonlinear long waves is investigated both theoretically and experimentally. A numerical method employing finite element techniques is used to solve the weakly nonlinear‐dispersive‐dissipative equations of motion for variable depth applied to this problem. Several dissipative effects also are included. The open sea conditions are simulated using a time varying radiative boundary condition imposed at a finite distance from the harbor entrance. Experiments are conducted using continuous waves incident upon a narrow constant depth rectangular harbor; the results show that, for the lowest resonant mode, convective nonlinearities could be neglected and a linear dissipative solution is sufficient to describe the wave dynamics inside the harbor. For higher resonant modes nonlinear convective effects must be included. Using transient waves, good agreement is obtained between the experimental and theoretical results for a rectangular harbor with a linearly sloping bottom and a constant depth harbor with a trapezoidal planform. The theoretical method is applied to Hilo Bay, Hawaii, to investigate its response to incoming long waves.

A Large-Volume Pump System for Studies of the Vertical Distribution of Fish Larvae Under Open Sea Conditions

A large-volume pump system (2.8 m3 min-1) for sampling fish larvae under open-sea conditions is described. Comparative efficiency trials by day and night showed that the pump was generally as efficient, or in some cases more efficient, in capturing larvae than vertically hauled 200 μm WP2 nets, though there was some evidence of visual avoidance by particular larval size classes during daylight. The pump system is particularly appropriate for investigating fine-scale vertical aggregations (1–10 m3) of larval fish in relation to the distribution of their food organisms.INTRODUCTIONStudies of the distribution of larval fish and their food organisms in relation to physical structure in the water column require sampling techniques capable of resolving fine-scale temporal and spatial distributions. As an alternative to conventional nets, large-volume pumps, sampling at rates in excess of 1 m3 min-1; provide such a capability. Major benefits of using large pumps in addition to temporal and spatial resolution are that a wide range of sizes of plankton including larval fish can be sampled simultaneously in relation to physical and chemical properties of the water column; there is reliable control of the volume of sample filtered and problems of clogging of towed nets are avoided; long series of sequential samples can be taken in studies of small-scale distribution; and instrumentation with in situ CTD and fluorometers at the intake enables real-time control of sampling in relation to physical structure.General engineering considerations for using such pumps have been reviewed in detail by Miller &amp; Judkins (1981), and a particular area of application has been in power-plant entrainment studies in shallow fresh water (Portner &amp; Rhode, 1977; Bowles &amp; Merriner, 1978; Gale &amp; Mohr, 1978; Ney &amp; Schumacher, 1978; Elder et al. 1979; Leithiser, Ehrlich &amp; Thum, 1979; Cada &amp; Loar, 1982).

Statistics of Breaking Waves Observed as Whitecaps in the Open Sea

Conventional observations of waves carried out with a buoy in open sea conditions were supplemented with simultaneous visual observations of whitecaps to identify breaking events in the buoy records. A statistical wave-by-wave analysis of these records indicates that such seemingly obvious parameters as wave steepness or wave asymmetry cannot be used to separate breakers from nonbreakers and the breaking occurs at wave steepness values much less than the theoretically expected steepness of a limiting wave. The observed fraction of breaking waves varied from about 0.10 to about 0.16, depending on wind speed. Two-thirds of the breaking waves were breaking in one-third of the wave groups for which a Hrms-threshold definition was used.

Dispersant effectiveness evaluation in a dynamic flow-through system: The IFP dilution test

The Institut Français du Pétrole has developed a dynamic flow-through test for assessing both the effectiveness of dispersants and their lethal toxic effects. The test simulates open sea conditions in that stirring takes place near the surface and oil concentrations decrease with time. The test procedure has also been found to be useful in examining the effect of dispersant oil ratios, oil properties and physical parameters on the effectiveness of dispersants.

Experimental studies on a perforated horizontal floating plate breakwater

Abstract In recent years floating breakwaters are considered for creating calm basin under open sea conditions for short period of time. In this paper, experimental studies on the performance characteristics of a horizontal floating plate breakwater are presented. The results of this two-dimensional model study are for regular waves of shallow and intermediate water depths. Analysis of the results shows that the transmission coefficient is strongly influenced by wave steepness and relative length of breakwater. It is also found to be dependent, to a lesser extent, on the relative depth of draft. Mooring forces are found to increase with increasing wave steepness and relative depth of draft. The performance of this breakwater is compared with other types of breakwater reported by earlier workers.

Occurrence, Habitat Use, and Behavior of Seabirds, Marine Mammals, and Arctic Cod at the Pond Inlet Ice Edge

In 1979, 17 species of birds were seen during studies near the Pond Inlet ice edge. Northern fulmars (Fulmarus glacialis) black-legged kittiwakes (Rissa tridactyla) thick billed murres (Uria lomvia) and black guillemots (Cepphus grylle) all avoided the ice edge when bordered with heavy pack ice and all but kittiwakes used the ice edge primarily for feeding. Guillemots and fulmars occurred in highest numbers in water along rough and moderately rough landfast ice: murres and kittiwakes showed no preference for such areas or for the other habitat surveyed (smooth landfast ice). Narwhals (Monodon monoceros) white whales (Delphinapterus leucas) and ringed seals (Phoca hispida) were the only marine mammals common at the ice edge. Whales repeatedly dived under the edge - probably feeding, searching for open water west of the ice edge, or both. Densities of seals near the ice edge were higher than elsewhere on landfast ice. Divers observed arctic cod (Boreogadus saida) close to the undersurface of landfast ice. Fish offshore were generally smaller, younger, and smaller-at-age than those inshore. Offshore, arctic cod were more numerous in areas with a rough under-ice surface than under smooth ice. Cod concentrated in crevices within rough under-ice surfaces. Inshore, cod were captured from ice cracks over shallow water. I conclude that vertebrates occur at ice edges for one or more of several reasons. Ringed seals and arctic cod live in close association with landfast ice: they probably occur near ice edges simply because landfast ice is present there. Ice edges seem to be primarily barriers against the further movements of whales toward summering locations. Finally, for murres and some other birds, ice edges seem to be favored feeding locations (relative to open sea conditions) due to greater access to preferred foods.Key words: arctic seabirds, ringed seal, narwhal, arctic cod, ice edges, Pond Inlet, habitat use, behavior, arctic waters, Lancaster Sound, Baffin Bay

Numerical computations of the storm surges in tosa bay

The storm surges which occurred in Tosa Bay in August 21, 1970 were numerically simulated. First of all NOAA's model “SPLASH” (Special Program to List Amplitudes of Surges from Hurricanes) was used and the effects of the typhoon's parameters, the bottom topography, the coastal configuration and the coordinate systems of storm surges were examined. “SPLASH” was then modified to suit computations of storm surges in the open sea and open boundary conditions were studied. Finally a two layer model was developed and the effects of the two layer system on surges were investigated.