Constant-depth Model Research Articles

A novel maximum likelihood based method for mapping depth and water quality from hyperspectral remote-sensing data

This article presents a novel statistical method for mapping water column properties from hyperspectral remote-sensing data. Usual inversion methods are based on a pixel-by-pixel approach. Therefore, they do not consider the spatial correlation between neighboring pixels, even though such pixels are often affected by the same water column if the spatial resolution is high enough.The proposed method uses such redundant information performing local maximum likelihood (ML) estimation of depth and water quality in large zones. It provides multi-resolution maps, in which resolution depends on local depth. In shallow water, the signal-to-noise ratio is high so an accurate mapping can be performed. Therefore, we propose to model local depth variations with a linear model while water quality is still supposed to be locally homogeneous. In deep water, the signal-to-noise ratio is lower so estimating only the local mean depth with standard ML estimation is more robust and reliable. The entire image is divided into appropriate meshes. In every mesh, water column properties are estimated using both linear and constant depth models. Final maps are obtained combining these estimates. The deeper the water, the higher the influence of standard ML estimation maps. Using local information provided by neighboring pixels makes this method robust to noise. Moreover, the hyperspectral image and estimated bathymetry have the same resolution in shallow water since depth is modeled for every pixel.The efficiency of our method was assessed with simulated and real hyperspectral images. Results proved that depth modeling improves depth and water quality estimations, especially in shallow water. In deep water, assuming that the bottom is locally flat is reasonable since depth variations are small relatively to depth mean value. With the considered water quality, the estimated bathymetry was accurate for depths up to 14m. Estimated concentration maps were consistent for the whole range of depths. The spatial resolution of estimated bathymetry was 50cm in shallow water (for depths up to 10m), and ranged from 2.5m to 5m in deep water (for depths between 10m and 14m).The influence of bio-optical modeling is also demonstrated. We show that reliable models are absolutely necessary to obtain good estimation results.

Layer-based sparse representation of multiview images

This article presents a novel method to obtain a sparse representation of multiview images. The method is based on the fact that multiview data is composed of epipolar-plane image lines which are highly redundant. We extend this principle to obtain the layer-based representation, which partitions a multiview image dataset into redundant regions (which we call layers) each related to a constant depth in the observed scene. The layers are extracted using a general segmentation framework which takes into account the camera setup and occlusion constraints. To obtain a sparse representation, the extracted layers are further decomposed using a multidimensional discrete wavelet transform (DWT), first across the view domain followed by a two-dimensional (2D) DWT applied to the image dimensions. We modify the viewpoint DWT to take into account occlusions and scene depth variations. Simulation results based on nonlinear approximation show that the sparsity of our representation is superior to the multi-dimensional DWT without disparity compensation. In addition we demonstrate that the constant depth model of the representation can be used to synthesise novel viewpoints for immersive viewing applications and also de-noise multiview images.

Chemical Mechanical Polishing 공정에 관한 원자단위 반응 모델링

This paper shows the results of atomistic modeling for the Interaction between spherical nano abrasive and substrate In chemical mechanical polishing processes. Atomistic modeling was achieved from 2-dimensional molecular dynamics simulations using the Lennard-jones 12-6 potentials. We proposed and investigated three mechanical models: (1) Constant Force Model; (2) Constant Depth Model, (3) Variable Force Model, and three chemical models, such as (1) Chemically Reactive Surface Model, (2) Chemically Passivating Surface Model, and (3) Chemically Passivating-reactive Surface Model. From the results obtained from classical molecular dynamics simulations for these models, we concluded that atomistic chemical mechanical polishing model based on both Variable Force Model and Chemically Passivating-reactive Surface Model were the most suitable for realistic simulation of chemical mechanical polishing in the atomic scale. The proposed model can be extended to investigate the 3-dimensional chemical mechanical polishing processes in the atomic scale.

Detachment folds with fixed hinges and variable detachment depth, northeastern Brooks Range, Alaska

Detachment anticlines in the northeastern Brooks Range accommodated displacement above a detachment by buckling of a competent unit over an incompetent unit. Meso- and microstructures in hinges and a lack of relict hinge structures in limbs suggest that these folds grew with fixed hinges. The structural thickness of the incompetent unit beneath the folds (detachment depth) varies from less than to greater than the stratigraphic thickness. A model in which incompetent unit thickness varies with fold area better approximates the geometry of the folds than does a more conventional constant-depth model. Additional discrepancies between modelled and observed incompetent unit thickness and field observations suggest non-plane strain and/or transport of material through the boundaries of the fold in the plane of the cross-section. The results of this study suggest a typical evolutionary sequence for detachment folds in the northeastern Brooks Range, which may be applicable elsewhere. Anticlines initiate as fixed-hinge buckle folds. Rapid initial increase in anticlinal cross-sectional area results in a decrease in incompetent unit thickness. Fold area begins to decrease with tightening beyond an interlimb angle of 90 dg. Decreasing fold area is accommodated through some combination of structural thickening of the incompetent unit, transport of solid or dissolved material out of the plane of section, transport of material through the boundaries of the fold in the plane of the cross-section, and/or truncation by thrust faults.

Transient Long-Wave Response for a Multiple-Island System

Abstract An interpretation of the tsunami response at the Hawaiian island of Kauai has been carried out utilizing simple geometric representations which include the three-island system of Kauai, Niihau and Oahu. The response has been investigated in terms of constant-depth models with the islands represented as cylinders and with a model which have geometric approximations of the underwater topography. The constant-depth models have indicated the portion of the response at Kauai related to interactions of the scattered and incident waves while the topographic model additionally contains response modes associated with the transient trapping of long-wave energy by the island system. The enhancement of the computed response in the topographic model is studied both in terms of the local Kauai topography alone and for a complete geometric representation of the Kauai, Niihau and Oahu topography.

Wind-Driven Model for Evaporite Deposition in a Layered Sea

Deposition of evaporites in a salinity- and density-layered sea is examined by theoretically predicting the large-scale circulation in a simplified model sea. In the constant depth model sea, vertical stratification is represented by two homogeneous layers; the upper layer is normal or slightly concentrated sea water, and the considerably denser lower layer is saturated with respect to halite. Each layer has a constant density and volume for all time. The horizontal transport form of the time-dependent equations of motion and continuity for each layer are solved numerically by a finite-difference method. A forward time extrapolation of four transport components, upper layer depth, and free surface height is performed on a square lattice covering the model basin. Interface stresses acting between the two layers and bottom stresses acting between the lower layer and the bottom allow consideration of vertical turbulent friction. Forcing is by a constant and uniform wind stress acting on the free surface. Rotation and hydrostatic pressure gradient terms are also included in the equations of motion. Several 140-hr (5.8 days) calculations were made for the Upper Silurian evaporites in Michigan Basin, using reasonable values of physical parameters. For an initially static sea 120 m deep with a 5-m-deep upper layer, mild easterly paleowinds cause upwelling of the lower layer at the north boundary. As the wind continues to blow, the region of upwelling slowly increases in area and migrates around the margin to the east boundary. In an evaporite sea, salt would precipitate in the exposed lower-layer brine because of evaporation. The salt could precipitate at the free surface as hopper crystals, internally, or at the bottom. By assuming a modest evaporation rate of 10 cm per yr, model calculations show that the total Upper Silurian salt volume is easily accounted for by an average of fewer than two 140-hr wind events per year. Model predicted upwelling at the north and east boundaries indicates that hopper crystals should be concentrated around the northeast margin of Michigan Basin. Other regional sedimentological and chemical variations related to circulation patterns, such as lithology and reef type, are suggested by the model calculations.

A Numerical Model for Circulation in a Homogeneous World Ocean

The results for two steady-state models of the world's ocean circulation are presented. The first model is of a homogeneous constant depth ocean with natural coastline geography. The second model, in addition, incorporates realistic sea floor topography. The flow fields indicate that in the constant depth ocean a coefficient of body friction R=1.5×10−6 see−1 is required to produce the observed Circumpolar Transport. For this model the magnitude of the Circumpolar Current is approximately proportional to the inverse of the friction parameter whereas in the variable depth model the effect of the frictional processes on the circumpolar circulation is of minor importance. The circulation is primarily determined by the sea floor topography, and the transport of the Circumpolar Current is small (∼16×1012 gm sec−1). The gyres in the ocean basins, however, are of magnitudes comparable with the constant depth model.

Baroclinic Boundary Currents and Long Edge-Waves in Basins with Sloping Shores

Earlier work on baroclinic “coastal jets” and Kelvin waves in constant-depth basins is extended to basins with sloping shores. Baroclinic coastal jets are again found to be set up by an inflow or outflow of water to or from the shore zone, but the center of these is now somewhat displaced from shore (under typical Great Lakes conditions by a distance of order 10 km). Shore-bound waves (edge-waves) of long wavelength are found to be possible only at frequencies below the inertial and are associated with quasi-geostrophic flow. Moreover, these waves propagate in the same sense as Kelvin waves. However, an infinite sequence of such edge-waves appear, replacing the simple Kelvin waves of the constant-depth model (of given wavelength). The frequency of all of these is well below the Kelvin wave frequency in a constant depth basin. The structure of the basic mode is very similar to that in a constant-depth basin, but that of the higher modes becomes progressively more complex, containing bands of opposing currents.