Dereverberation of marine reflection seismic data by a spatial combination of predictive deconvolution and velocity filtering

Contamination of seismic reflection records at early times by first-order water reverberations can be especially severe during survey operations over hard and flat sea floors on the continental shelf or in lake environments. A new dereverberation scheme based on two classical techniques — predictive deconvolution and velocity filtering — has been developed to address this problem. The techniques are combined spatially to take advantage of their complementary offset- and time-dependent properties. Stage I of the scheme consists of applying predictive deconvolution at short offset. The data are previously conditioned by a normal moveout correction with the water velocity which restores the periodicity of the reverberations in the offset-time plane and enhances the performance of deconvolution. Stage II of the scheme involves velocity filtering in the common-midpoint domain which is particularly effective at long offset where the moveout difference between primary reflections and reverberations is largest. The dereverberation scheme is well suited for the initial processing of large volumes of data due to the general availability of cost-effective deconvolution and velocity filtering algorithms in seismic processing software packages. Practical implementation issues are illustrated by a field example from the GLIMPCE survey in Lake Superior.Lithoprobe Publication No. 475.     

The directional radiation of long waves from bottom deformations of finite duration

The process of generation of two-dimensional (2D) wave motions during small elliptical displacements of the bottom which occur for a finite time interval is considered within the framework of the linear theory of long waves in a basin of constant depth. The spatial structure and the amplitudinal and energy characteristics of the emerging directional surface wave are analysed for bottom deformations of a special form.Translated by Mikhail M. Trufanov.     

The near field of internal waves after the moving area of atmospheric pressures

The near wave field generated by the travelling atmospheric pressure zone over a stratified fluid is studied within the framework of the linear theory of long waves allowing for the Coriolis force. The exact solution of the problem as a set of single integrals is deduced for the model distribution of pressures. The characteristics of the near wave field have been computed for the Väisälä-Brunt frequency profile takeu from observations. Their dependences on the geographical latitude and the wave generator travelling rate are analysed.Translated by Mikhail M. Trufanov.     

Submersible observations of an iceberg pit and scour on the Grand Banks of Newfoundland

An elongated sea bed depression (pit), 80 by 125 m and 10 m deep located on the Grand Banks of Newfoundland was identified on high resolution surficial geophysical survey lines and investigated using a manned submersible. The pit occurs at the termination of a long (greater than 3 km) iceberg scour, 1.5 m deep, and 80 m wide in 91 m of water. It is similar to other depressions in the region that indent the sea bed up to seven times deeper than the surrounding deepest iceberg furrows. The pit is interpreted to be the sea bed response to impact and loading by a rolling and grounding iceberg. The iceberg scour and pit appear to be of recent origin.     

Interactions of cadmium with the reproductive cycle of Mytilus edulis L.

Sublethal effects of cadmium on reproduction can have detrimental consequences for the long-term survival, even of species with high LC₅₀ values. The sea mussel, Mytilus edulis, is well-known for its use in biomonitoring work due to its relatively low sensitivity towards many toxicants, including cadmium.¹ Because little is known on sublethal effects of this metal in invertebrates,^2–6 we have studied these effects, with emphasis on reproduction, by exposing mussels to 100 ppb cadmium in sea water. This concentration significantly inhibits follicle development in both male and female gonads, but has subsequently a stimulating effect on the spawning frequency. Due to these opposite effects the consequences of cadmium stress for gamete production are expected to be small, as the average number of gametes released by spawning animals was not significantly changed.     

Field Placement and Evaluation of Stabilized Dredged Material (SDM) from the New York/New Jersey Harbor

Since the 1997 local ban on ocean dumping of dredged sediments, the States of New York and New Jersey have pursued a policy of environmentally sound solutions to the management of dredged material, including beneficial use of stabilized dredged material (SDM) in transportation applications. A pilot study was initiated in 1998 to evaluate the use of SDM in the construction of highway embankments. Utilizing 80,000 cubic yards of dredged material, two embankments were constructed from SDM on a commercial development area adjacent to the Harbor. Geotechnical properties and handling of SDM were evaluated both during and one year post - construction. This article presents the evaluation of the embankments themselves, including constructability and performance. The results demonstrate that SDM satisfies most of the geotechnical criteria for fill construction, except those for durability, requiring proper coverage and protection similar to that provided for fills constructed on cohesive soils. This same characteristic precludes long term stockpiling of SDM prior to final placement, limiting applications to those that have schedules overlapping with dredging projects. Increased costs for the use of SDM can be as high as $8 per cubic yard over traditional fills; however, this cost may be recouped through management fees collected from dredging projects.     

Hadley and Rossby regimes in a simple model of convection of a rotating fluid

This paper analyzes the properties of solutions to the equations describing the motion of a stratified fluid in the class of velocity and temperature fields linear in coordinates. For an ideal fluid, these equations, on the one hand, are exact for the corresponding hydrodynamic problem and, on the other hand, are identical to the equations of motion for a heavy top. In a conservative case, the equations of motion of a top share common solutions with the equations of geophysical fluid dynamics and reproduce motions similar to those existing in the theory of the large-scale atmospheric circulation. This study considers the effects of viscosity and heat conduction in the fluid, which are, in a sense, similar to the effect of friction in the case of a top. The influence of deflections of the vectors of gravity and external rotation from their standard directions for a plane-parallel atmosphere is also considered. The regimes of motions that are described by the starting equations and approximations commonly used to model the atmospheric general circulation (the quasi-geostrophic approximation) are analyzed. It is shown that these equations correctly describe the Hadley and Rossby circulation regimes and transitions between them that are observed in numerical and laboratory experiments. Particular attention is given to the consistency between different regimes of the exact equations and their quasi-geostrophic approximations, which is manifested for small Rossby numbers and is generally absent for large Rossby numbers. The asymptotic behaviors of the curves of transition between the Hadley and Rossby regimes under the conditions of breaking the external symmetry of flows are obtained. These asymptotics explain the corresponding transition boundaries for the regimes observed in the known experiments in annuluses.