Laurent White - Academia.edu (original) (raw)

Papers by Laurent White

Research paper thumbnail of Development of a marine modelling benchmark: tidal circulation around Rattray Island

A self-forming working group is setting up reference benchmarks usable for the next decade or mor... more A self-forming working group is setting up reference benchmarks usable for the next decade or more. They should be applicable for current and future generations of models 1 . These benchmarks should be a new valuable tool for the development of future ocean models. In the scope of the SLIM 2 project, a test-case is developed focusing on the circulation around Rattray Island (Great Barrier Reef, Northeast Australia), which is mainly influenced by tidal forcing. Field measurements and visual observations showed that stable eddies develop in the wake of the island at rising and falling tides. The water turbidity downstream of the island suggests the existence of a strong upwelling that would be responsible for carrying sediments from the sea bed to the sea surface. The model should be able to simulate the eddies downstream of the island, con-forming with available data from currentmeters and visual observations, and simu-late the upwelling generated within theses eddies. All the data n...

Research paper thumbnail of Flow separation and vertical motions in a tidal flow interacting with a shallow-water island

Estuarine, Coastal and Shelf Science, 2008

This paper reports on the case study of Rattray Island (Great Barrier Reef, northeast Australia),... more This paper reports on the case study of Rattray Island (Great Barrier Reef, northeast Australia), lying perpendicular to tidal flow in shallow waters. At ebb and flood, attached (stable) eddies develop in the wake where swirls of turbidity suggest that sediment-laden waters are brought to the surface as a result of vertical transport. Both eddy and tip upwellings are encountered in the tidal flow around Rattray Island but there is currently no clear-cut answer as to which secondary flow generates upwelling with the largest intensity. This paper addresses this specific issue through idealized and realistic high-resolution numerical experiments. The analysis is supported by physical arguments based on the theory of flow separation. Given Rattray's geometry and surrounding bathymetry, the mechanism of flow separation in shallow waters helps explain the asymmetry in size of the eddies and their intensity. The results of idealized numerical experiments also suggest that eddy and tip upwellings may be of similar intensity at Rattray Island.

Research paper thumbnail of Free and forced thermocline oscillations in Lake Tanganyika

All year long, the thermocline of Lake Tanganyika (Central Africa) oscillates about two equilibri... more All year long, the thermocline of Lake Tanganyika (Central Africa) oscillates about two equilibrium states. The thermocline is tilted downward toward the north during the dry season, due to the wind bringing the warm surface water from south to north. The equilibrium position of the thermocline is horizontal during the wet season. The oscillations about these two equilibrium states may be of two types. The free oscillations are due to the seasonal cycle of the wind stress, while the forced oscillations are a direct response to the intraseasonal variability of the surface forcing. It has already been suggested that both have a three- to four- week oscillation period. The Factor Separation method is here used to show that the forced oscillations of the thermocline are about twice as large as the free ones.

Research paper thumbnail of Free and forced thermocline oscillations in

Research paper thumbnail of Finite element hydrodynamic modelling in Lake Tanganyika

Research paper thumbnail of A three-dimensional unstructured mesh finite element shallow-water model, with application to the flows around an island and in a wind-driven, elongated basin

Ocean Modelling, 2008

We present a new three-dimensional, unstructured mesh finite element shallow-water model. The cur... more We present a new three-dimensional, unstructured mesh finite element shallow-water model. The current configuration is suitable for studying unstratified flows and the evolution of passive tracers. The model has a free surface and is hydrostatic. The mesh is unstructured in the horizontal and extruded towards the seabed in the direction parallel to the local gravity vector to generate a mesh made up of prisms. The mesh moves in the vertical and accommodates the free-surface motions. We describe the numerical treatment of the hydrodynamical equations with the finite element method. A discontinuous representation is used in the vertical for all velocity components. The horizontal velocity components are non-conforming in the horizontal, which is particularly appropriate for advection-dominated flows. The model is validated against a realistic tidal flow around a shallow-water island for which field measurements are available and is shown to operate successfully. The three-dimensional character of the flow is emphasized by use of a passive tracer. We also assess the model's ability to represent the vertical structure of the horizontal flow field by applying it to a wind-driven flow experiment in an elongated rectangular basin. *

Research paper thumbnail of A one-dimensional benchmark for the propagation of Poincaré waves

Ocean Modelling, 2006

Several numerical methods are employed to solve the linear shallow-water equations describing the... more Several numerical methods are employed to solve the linear shallow-water equations describing the propagation of Poincaré waves within a one-dimensional finite domain. An analytical solution to the problem, set off by a discontinuous steplike elevation, is known and allows for assessing the accuracy and robustness of each method and in particular their ability to capture the traveling discontinuities without generating spurious oscillations. The following methods are implemented: the method of characteristics, the Galerkin finite-element method (FEM) and the discontinuous Galerkin FEM with two different ways of computing the numerical fluxes.

Research paper thumbnail of Comparison of free-surface and rigid-lid finite element models of barotropic instabilities

Ocean Dynamics, 2006

Abstract The main goal of this work is to appraise the finite element method in the way it repres... more Abstract The main goal of this work is to appraise the finite element method in the way it represents barotropic instabilities. To that end, three different formulations are employed. The free-surface formulation solves the primitive shallow-water equations and is of predominant use for ocean modeling. The vorticity–stream function and velocity–pressure formulations resort to the rigid-lid approximation and are presented because theoretical results are based on the same approximation. The growth rates for all three formulations ...

Research paper thumbnail of Tracer Conservation for Three-Dimensional, Finite-Element, Free-Surface, Ocean Modeling on Moving Prismatic Meshes

Monthly Weather Review, 2008

Abstract Large-scale free-surface ocean models designed to run over climatic time scales are requ... more Abstract Large-scale free-surface ocean models designed to run over climatic time scales are required to globally conserve the volume and any tracer up to machine precision. In addition, local consistency is critical and requires that the discrete tracer equation preserve constants in a closed domain and if there is no tracer source or sink. Local consistency, together with monotonicity, will ensure that no spurious tracer extrema occur. A three-dimensional, finite-element, shallow-water model is presented. The mesh is unstructured ...

Research paper thumbnail of High-order regridding–remapping schemes for continuous isopycnal and generalized coordinates in ocean models

Journal of Computational Physics, 2009

A hierarchy of high-order regridding–remapping schemes for use in generalized vertical coordinate... more A hierarchy of high-order regridding–remapping schemes for use in generalized vertical coordinate ocean models is presented. The proposed regridding–remapping framework is successfully used in a series of idealized one-dimensional numerical experiments as well as two-dimensional internal wave and overflow test cases. The model is capable of replicating z-, sigma- and isopycnal-coordinate results, among others. Particular emphasis is placed on the

Research paper thumbnail of A high-order finite volume remapping scheme for nonuniform grids: The piecewise quartic method (PQM)

Journal of Computational Physics, 2008

A hierarchy of one-dimensional high-order remapping schemes is presented and their performance wi... more A hierarchy of one-dimensional high-order remapping schemes is presented and their performance with respect to accuracy and convergence rate investigated. The schemes are also compared based on remapping experiments in closed domains. The piecewise quartic method (PQM) is presented, based on fifth-order accurate piecewise polynomials, and is motivated by the need to significantly improve hybrid coordinate systems of ocean climate models, which require the remapping to be conservative, monotonic and highly accurate. A limiter for this scheme is fully described that never decreases the polynomial degree, except at the location of extrema. We assess the use of high-order explicit and implicit (i.e., compact) estimates for the edge values and slopes needed to build the piecewise polynomials in both piecewise parabolic method (PPM) and PQM. It is shown that all limited PQM schemes perform significantly better than limited PPM schemes and that PQM schemes are much more cost-effective.

Research paper thumbnail of Diagnoses of vertical transport in a three-dimensional finite element model of the tidal circulation around an island

Estuarine, Coastal and Shelf Science, 2007

A three-dimensional finite element model is used to investigate the formation of shallow-water ed... more A three-dimensional finite element model is used to investigate the formation of shallow-water eddies in the wake of Rattray Island (Great Barrier Reef, Australia). Field measurements and visual observations show that stable eddies develop in the lee of the island at rising and falling tides. The water turbidity downstream of the island suggests the existence of strong upwelling that would be responsible for carrying bed sediments up to the sea surface. We first propose to look at the upwelling velocity and then use the theory of the age to diagnose vertical transport. The water age is defined as the time elapsed since particles of water left the sea bottom, where the age is prescribed to be zero. Two versions of this diagnosis are considered. Although the model predicts upwelling within the eddies, it is not sufficiently intense to account for vertical transport throughout the water column during the life span of the eddies. As mesh resolution increases, this upwelling does not intensify. However, strong upwelling is then resolved off the island's tips, which is confirmed by the results obtained with the age. This study also shows that the finite element method, together with unstructured meshes, performs well for representing three-dimensional flow past an island.

Research paper thumbnail of Toward a generic method for studying water renewal, with application to the epilimnion of Lake Tanganyika

Estuarine, Coastal and Shelf Science, 2007

We present a method, based on the concept of age and residence time, to study the water renewal i... more We present a method, based on the concept of age and residence time, to study the water renewal in a semi-enclosed domain. We split the water of this domain into different water types. The initial water is the water initially present in the semi-enclosed domain. The renewing water is defined as the water entering the domain of interest. Several renewing water types may be considered depending on their origin. We present the equations for computing the age and the residence time of a certain water type. These timescales are of use to understand the rate at which the water renewal takes place. Computing these timescales can be achieved at an acceptable extra computer cost.

Research paper thumbnail of Influence of the turbulence closure scheme on the finite-element simulation of the upwelling in the wake of a shallow-water island

Continental Shelf Research, 2007

A three-dimensional finite-element model is used to investigate the tidal flow around Rattray Isl... more A three-dimensional finite-element model is used to investigate the tidal flow around Rattray Island, Great Barrier Reef, Australia. Field measurements and visual observations show both stable eddies developing at rising and falling tide in the wake of the island. The water turbidity suggests intense upwelling able to carry bed sediments upwards. Based on previous numerical studies, it remains unclear at this point whether the most intense upwelling occurs near the centre of the eddies or off the island's tips, closer to the island. All these studies resorted to a very simple turbulence closure, with a zeroequation model whereby the coefficient of vertical viscosity is computed via an algebraic expression. In this work, we aim at studying the influence of the turbulence closure on model results, with emphasis on the prediction of vertical motions. The Mellor and Yamada level 2.5 closure scheme is used and an increase in the intensity of vertical transport is observed. This increase is partly explained by the fact that the Mellor and Yamada model takes into account the hysteresis effect in the time variation of turbulence variables. The influence of the advection of turbulence variables is estimated to be negligible. By a better representation of transient coastal phenomena, the Mellor and Yamada level 2.5 turbulence closure improves the model to a significant degree. r

Research paper thumbnail of Tracer Conservation and Local Consistency for Three-Dimensional, Finite Element, Free-Surface Ocean Modeling on Moving Prismatic Meshes

Large-scale free-surface ocean models designed to run over climatic timescales are required to gl... more Large-scale free-surface ocean models designed to run over climatic timescales are required to globally conserve the volume and any tracer up to machine precision. In addition, the following property is critical. Setting a tracer concentration to a uniform value throughout the closed domain and letting the free surface undulate, the same tracer concentration must be recovered at any later time if there is no tracer source. This property of consistency, together with monotonicity, will ensure that no spurious tracer extrema occur. ...

Research paper thumbnail of Filtering the signature of submerged large woody debris from bathymetry data

Journal of Hydrology, 2005

Modeling water velocities and depth for riverine aquatic habitat analysis requires fine-scale sur... more Modeling water velocities and depth for riverine aquatic habitat analysis requires fine-scale surveys of river bathymetry. The presence of submerged large woody debris (LWD) distorts the results of acoustic bathymetry surveys and subsequent modeling if the LWD data is not separated from the background river bathymetry. Submerged LWD typically appears in digital acoustic data for a low-gradient sand-bed river as impulse spikes of a few data points with a substantially shallower depth than the surrounding data. This paper examines the performance of linear and nonlinear filtering algorithms for removing impulse spikes from a digital bathymetry signal. A synthesized data set is used for control tests that quantify the error associated with each method. The more successful nonlinear filtering techniques (median and erosion filters) are used to filter single-beam echosounder data, from the Sulphur River in northeastern Texas, USA. Median filtering proved to be the best technique for removing LWD impulse spikes while leaving the background bathymetry relatively unchanged. Efficient automation of spike removal from a data set requires a method for selecting the filter characteristics without recourse to engineering judgment or prior experience. A method of a priori selecting the minimum filter order based upon the physical scales of the LWD and the statistics of the data separation in the survey is proposed based on scaling analysis, and validated with the study results.

Research paper thumbnail of Development of a marine modelling benchmark: tidal circulation around Rattray Island

A self-forming working group is setting up reference benchmarks usable for the next decade or mor... more A self-forming working group is setting up reference benchmarks usable for the next decade or more. They should be applicable for current and future generations of models 1 . These benchmarks should be a new valuable tool for the development of future ocean models. In the scope of the SLIM 2 project, a test-case is developed focusing on the circulation around Rattray Island (Great Barrier Reef, Northeast Australia), which is mainly influenced by tidal forcing. Field measurements and visual observations showed that stable eddies develop in the wake of the island at rising and falling tides. The water turbidity downstream of the island suggests the existence of a strong upwelling that would be responsible for carrying sediments from the sea bed to the sea surface. The model should be able to simulate the eddies downstream of the island, con-forming with available data from currentmeters and visual observations, and simu-late the upwelling generated within theses eddies. All the data n...

Research paper thumbnail of Flow separation and vertical motions in a tidal flow interacting with a shallow-water island

Estuarine, Coastal and Shelf Science, 2008

This paper reports on the case study of Rattray Island (Great Barrier Reef, northeast Australia),... more This paper reports on the case study of Rattray Island (Great Barrier Reef, northeast Australia), lying perpendicular to tidal flow in shallow waters. At ebb and flood, attached (stable) eddies develop in the wake where swirls of turbidity suggest that sediment-laden waters are brought to the surface as a result of vertical transport. Both eddy and tip upwellings are encountered in the tidal flow around Rattray Island but there is currently no clear-cut answer as to which secondary flow generates upwelling with the largest intensity. This paper addresses this specific issue through idealized and realistic high-resolution numerical experiments. The analysis is supported by physical arguments based on the theory of flow separation. Given Rattray's geometry and surrounding bathymetry, the mechanism of flow separation in shallow waters helps explain the asymmetry in size of the eddies and their intensity. The results of idealized numerical experiments also suggest that eddy and tip upwellings may be of similar intensity at Rattray Island.

Research paper thumbnail of Free and forced thermocline oscillations in Lake Tanganyika

All year long, the thermocline of Lake Tanganyika (Central Africa) oscillates about two equilibri... more All year long, the thermocline of Lake Tanganyika (Central Africa) oscillates about two equilibrium states. The thermocline is tilted downward toward the north during the dry season, due to the wind bringing the warm surface water from south to north. The equilibrium position of the thermocline is horizontal during the wet season. The oscillations about these two equilibrium states may be of two types. The free oscillations are due to the seasonal cycle of the wind stress, while the forced oscillations are a direct response to the intraseasonal variability of the surface forcing. It has already been suggested that both have a three- to four- week oscillation period. The Factor Separation method is here used to show that the forced oscillations of the thermocline are about twice as large as the free ones.

Research paper thumbnail of Free and forced thermocline oscillations in

Research paper thumbnail of Finite element hydrodynamic modelling in Lake Tanganyika

Research paper thumbnail of A three-dimensional unstructured mesh finite element shallow-water model, with application to the flows around an island and in a wind-driven, elongated basin

Ocean Modelling, 2008

We present a new three-dimensional, unstructured mesh finite element shallow-water model. The cur... more We present a new three-dimensional, unstructured mesh finite element shallow-water model. The current configuration is suitable for studying unstratified flows and the evolution of passive tracers. The model has a free surface and is hydrostatic. The mesh is unstructured in the horizontal and extruded towards the seabed in the direction parallel to the local gravity vector to generate a mesh made up of prisms. The mesh moves in the vertical and accommodates the free-surface motions. We describe the numerical treatment of the hydrodynamical equations with the finite element method. A discontinuous representation is used in the vertical for all velocity components. The horizontal velocity components are non-conforming in the horizontal, which is particularly appropriate for advection-dominated flows. The model is validated against a realistic tidal flow around a shallow-water island for which field measurements are available and is shown to operate successfully. The three-dimensional character of the flow is emphasized by use of a passive tracer. We also assess the model's ability to represent the vertical structure of the horizontal flow field by applying it to a wind-driven flow experiment in an elongated rectangular basin. *

Research paper thumbnail of A one-dimensional benchmark for the propagation of Poincaré waves

Ocean Modelling, 2006

Several numerical methods are employed to solve the linear shallow-water equations describing the... more Several numerical methods are employed to solve the linear shallow-water equations describing the propagation of Poincaré waves within a one-dimensional finite domain. An analytical solution to the problem, set off by a discontinuous steplike elevation, is known and allows for assessing the accuracy and robustness of each method and in particular their ability to capture the traveling discontinuities without generating spurious oscillations. The following methods are implemented: the method of characteristics, the Galerkin finite-element method (FEM) and the discontinuous Galerkin FEM with two different ways of computing the numerical fluxes.

Research paper thumbnail of Comparison of free-surface and rigid-lid finite element models of barotropic instabilities

Ocean Dynamics, 2006

Abstract The main goal of this work is to appraise the finite element method in the way it repres... more Abstract The main goal of this work is to appraise the finite element method in the way it represents barotropic instabilities. To that end, three different formulations are employed. The free-surface formulation solves the primitive shallow-water equations and is of predominant use for ocean modeling. The vorticity–stream function and velocity–pressure formulations resort to the rigid-lid approximation and are presented because theoretical results are based on the same approximation. The growth rates for all three formulations ...

Research paper thumbnail of Tracer Conservation for Three-Dimensional, Finite-Element, Free-Surface, Ocean Modeling on Moving Prismatic Meshes

Monthly Weather Review, 2008

Abstract Large-scale free-surface ocean models designed to run over climatic time scales are requ... more Abstract Large-scale free-surface ocean models designed to run over climatic time scales are required to globally conserve the volume and any tracer up to machine precision. In addition, local consistency is critical and requires that the discrete tracer equation preserve constants in a closed domain and if there is no tracer source or sink. Local consistency, together with monotonicity, will ensure that no spurious tracer extrema occur. A three-dimensional, finite-element, shallow-water model is presented. The mesh is unstructured ...

Research paper thumbnail of High-order regridding–remapping schemes for continuous isopycnal and generalized coordinates in ocean models

Journal of Computational Physics, 2009

A hierarchy of high-order regridding–remapping schemes for use in generalized vertical coordinate... more A hierarchy of high-order regridding–remapping schemes for use in generalized vertical coordinate ocean models is presented. The proposed regridding–remapping framework is successfully used in a series of idealized one-dimensional numerical experiments as well as two-dimensional internal wave and overflow test cases. The model is capable of replicating z-, sigma- and isopycnal-coordinate results, among others. Particular emphasis is placed on the

Research paper thumbnail of A high-order finite volume remapping scheme for nonuniform grids: The piecewise quartic method (PQM)

Journal of Computational Physics, 2008

A hierarchy of one-dimensional high-order remapping schemes is presented and their performance wi... more A hierarchy of one-dimensional high-order remapping schemes is presented and their performance with respect to accuracy and convergence rate investigated. The schemes are also compared based on remapping experiments in closed domains. The piecewise quartic method (PQM) is presented, based on fifth-order accurate piecewise polynomials, and is motivated by the need to significantly improve hybrid coordinate systems of ocean climate models, which require the remapping to be conservative, monotonic and highly accurate. A limiter for this scheme is fully described that never decreases the polynomial degree, except at the location of extrema. We assess the use of high-order explicit and implicit (i.e., compact) estimates for the edge values and slopes needed to build the piecewise polynomials in both piecewise parabolic method (PPM) and PQM. It is shown that all limited PQM schemes perform significantly better than limited PPM schemes and that PQM schemes are much more cost-effective.

Research paper thumbnail of Diagnoses of vertical transport in a three-dimensional finite element model of the tidal circulation around an island

Estuarine, Coastal and Shelf Science, 2007

A three-dimensional finite element model is used to investigate the formation of shallow-water ed... more A three-dimensional finite element model is used to investigate the formation of shallow-water eddies in the wake of Rattray Island (Great Barrier Reef, Australia). Field measurements and visual observations show that stable eddies develop in the lee of the island at rising and falling tides. The water turbidity downstream of the island suggests the existence of strong upwelling that would be responsible for carrying bed sediments up to the sea surface. We first propose to look at the upwelling velocity and then use the theory of the age to diagnose vertical transport. The water age is defined as the time elapsed since particles of water left the sea bottom, where the age is prescribed to be zero. Two versions of this diagnosis are considered. Although the model predicts upwelling within the eddies, it is not sufficiently intense to account for vertical transport throughout the water column during the life span of the eddies. As mesh resolution increases, this upwelling does not intensify. However, strong upwelling is then resolved off the island's tips, which is confirmed by the results obtained with the age. This study also shows that the finite element method, together with unstructured meshes, performs well for representing three-dimensional flow past an island.

Research paper thumbnail of Toward a generic method for studying water renewal, with application to the epilimnion of Lake Tanganyika

Estuarine, Coastal and Shelf Science, 2007

We present a method, based on the concept of age and residence time, to study the water renewal i... more We present a method, based on the concept of age and residence time, to study the water renewal in a semi-enclosed domain. We split the water of this domain into different water types. The initial water is the water initially present in the semi-enclosed domain. The renewing water is defined as the water entering the domain of interest. Several renewing water types may be considered depending on their origin. We present the equations for computing the age and the residence time of a certain water type. These timescales are of use to understand the rate at which the water renewal takes place. Computing these timescales can be achieved at an acceptable extra computer cost.

Research paper thumbnail of Influence of the turbulence closure scheme on the finite-element simulation of the upwelling in the wake of a shallow-water island

Continental Shelf Research, 2007

A three-dimensional finite-element model is used to investigate the tidal flow around Rattray Isl... more A three-dimensional finite-element model is used to investigate the tidal flow around Rattray Island, Great Barrier Reef, Australia. Field measurements and visual observations show both stable eddies developing at rising and falling tide in the wake of the island. The water turbidity suggests intense upwelling able to carry bed sediments upwards. Based on previous numerical studies, it remains unclear at this point whether the most intense upwelling occurs near the centre of the eddies or off the island's tips, closer to the island. All these studies resorted to a very simple turbulence closure, with a zeroequation model whereby the coefficient of vertical viscosity is computed via an algebraic expression. In this work, we aim at studying the influence of the turbulence closure on model results, with emphasis on the prediction of vertical motions. The Mellor and Yamada level 2.5 closure scheme is used and an increase in the intensity of vertical transport is observed. This increase is partly explained by the fact that the Mellor and Yamada model takes into account the hysteresis effect in the time variation of turbulence variables. The influence of the advection of turbulence variables is estimated to be negligible. By a better representation of transient coastal phenomena, the Mellor and Yamada level 2.5 turbulence closure improves the model to a significant degree. r

Research paper thumbnail of Tracer Conservation and Local Consistency for Three-Dimensional, Finite Element, Free-Surface Ocean Modeling on Moving Prismatic Meshes

Large-scale free-surface ocean models designed to run over climatic timescales are required to gl... more Large-scale free-surface ocean models designed to run over climatic timescales are required to globally conserve the volume and any tracer up to machine precision. In addition, the following property is critical. Setting a tracer concentration to a uniform value throughout the closed domain and letting the free surface undulate, the same tracer concentration must be recovered at any later time if there is no tracer source. This property of consistency, together with monotonicity, will ensure that no spurious tracer extrema occur. ...

Research paper thumbnail of Filtering the signature of submerged large woody debris from bathymetry data

Journal of Hydrology, 2005

Modeling water velocities and depth for riverine aquatic habitat analysis requires fine-scale sur... more Modeling water velocities and depth for riverine aquatic habitat analysis requires fine-scale surveys of river bathymetry. The presence of submerged large woody debris (LWD) distorts the results of acoustic bathymetry surveys and subsequent modeling if the LWD data is not separated from the background river bathymetry. Submerged LWD typically appears in digital acoustic data for a low-gradient sand-bed river as impulse spikes of a few data points with a substantially shallower depth than the surrounding data. This paper examines the performance of linear and nonlinear filtering algorithms for removing impulse spikes from a digital bathymetry signal. A synthesized data set is used for control tests that quantify the error associated with each method. The more successful nonlinear filtering techniques (median and erosion filters) are used to filter single-beam echosounder data, from the Sulphur River in northeastern Texas, USA. Median filtering proved to be the best technique for removing LWD impulse spikes while leaving the background bathymetry relatively unchanged. Efficient automation of spike removal from a data set requires a method for selecting the filter characteristics without recourse to engineering judgment or prior experience. A method of a priori selecting the minimum filter order based upon the physical scales of the LWD and the statistics of the data separation in the survey is proposed based on scaling analysis, and validated with the study results.