Surface Topography Data Research Articles

Factors affecting the spatial pattern of bedrock groundwater recharge at the hillslope scale

AbstractThe spatial patterns of groundwater recharge on hillslopes with a thin soil mantle overlying bedrock are poorly known. Complex interactions between vertical percolation of water through the soil, permeability contrasts between soil and bedrock and lateral redistribution of water result in large spatial variability of water moving into the bedrock. Here, we combine new measurements of saturated hydraulic conductivity of soil mantle and bedrock of the well‐studied Panola Mountain experimental hillslope with previously collected (sub)surface topography and soil depth data to quantify the factors affecting the spatial pattern of bedrock groundwater recharge.We use geostatistical characteristics of the measured permeability to generate spatial fields of saturated hydraulic conductivity for the entire hillslope. We perform simulations with a new conceptual model with these random fields and evaluate the resulting spatial distribution of groundwater recharge during individual rainstorms and series of rainfall events. Our simulations show that unsaturated drainage from soil into bedrock is the prevailing recharge mechanism and accounts for 60% of annual groundwater recharge. Therefore, soil depth is a major control on the groundwater recharge pattern through available storage capacity and controlling the size of vertical flux. The other 40% of recharge occurs during storms that feature transient saturation at the soil‐bedrock interface. Under these conditions, locations that can sustain increased subsurface saturation because of their topographical characteristics or those with high bedrock permeability will act as hotspots of groundwater recharge when they receive lateral flow. Copyright © 2015 John Wiley & Sons, Ltd.

Contact mechanism of a rock fracture subjected to normal loading and its impact on fast closure behavior during initial stage of fluid flow experiment

SummaryFast closure of rock fractures has been commonly observed in the initial stage of fluid flow experiments at environmental temperatures under low or moderate normal stresses. To fully understand the mechanisms that drive this fast closure, the evolution of local stresses acting on contacting asperities on the fracture surfaces prior to fluid flow tests needs to be evaluated. In this study, we modeled numerically the asperity deformation and failure processes during initial normal loading, by adopting both elastic and elastic–plastic deformation models for the asperities on a real rock fracture with measured surface topography data, and estimated their impact on initial conditions for fluid flow test performed under laboratory conditions. Compared with the previous models that simulate the normal contact of a fracture as the approach of two rigid surfaces without deformations, our models of deformable asperities yielded smaller contact areas and higher stresses on contacting asperities at a given normal stress or normal displacement. The results show that the calculated local stresses were concentrated on the contacts of a few major asperities, resulting in crushing of asperity tips. With these higher contact stresses, however, the predicted closure rates by pressure solution are still several orders of magnitude lower than that of the experimental measurements at the initial stage of fluid flow test. This indicates that single pressure solution may not likely to be the principal compaction mechanism for this fast closure, and that the damages on contacting asperities that occur during the initial normal loading stage may play an important role. Copyright © 2015 John Wiley & Sons, Ltd.

Choice of reference surfaces for machined surface roughness in milling of SiCp/Al composites

In order to choose the appropriate reference surface on the machined surface roughness of SiCp/Al composites, the cutting experiments of SiCp/Al composites were carried out, and the machined surface topography was measured by OLS3000 Confocal laser scanning microscope. The 3D measured data of machined surface topography were analyzed by the area power spectrum density. The result shows that the texture of machined surface topography in milling of SiCp/Al composites is almost isotropic. This is the reason that the values of R q at different locations on the same machined surface are obviously different. Through the comparison of performance of different filtering methods, the robust least squares reference surface can be used to extract the surface roughness of SiCp/Al composites effectively.

Advanced geophysical underground coal gasification monitoring

Underground Coal Gasification (UCG) produces less surface impact, atmospheric pollutants and greenhouse gas than traditional surface mining and combustion. Therefore, it may be useful in mitigating global change caused by anthropogenic activities. Careful monitoring of the UCG process is essential in minimizing environmental impact. Here we first summarize monitoring methods that have been used in previous UCG field trials. We then discuss in more detail a number of promising advanced geophysical techniques. These methods – seismic, electromagnetic, and remote sensing techniques – may provide improved and cost-effective ways to image both the subsurface cavity growth and surface subsidence effects. Active and passive seismic data have the promise to monitor the burn front, cavity growth, and observe cavity collapse events. Electrical resistance tomography (ERT) produces near real time tomographic images autonomously, monitors the burn front and images the cavity using low-cost sensors, typically running within boreholes. Interferometric synthetic aperture radar (InSAR) is a remote sensing technique that has the capability to monitor surface subsidence over the wide area of a commercial-scale UCG operation at a low cost. It may be possible to infer cavity geometry from InSAR (or other surface topography) data using geomechanical modeling. The expected signals from these monitoring methods are described along with interpretive modeling for typical UCG cavities. They are illustrated using field results from UCG trials and other relevant subsurface operations.

Machining of Injection Mould Materials for Different Cutting Flute in Low-Speed End Milling

The complexity of mould shapes and the hardness of the mould material contribute to difficulties in machining. Examination of the capability of atypeof cutting tool (Tungsten Carbide Ball Nose) towards machining mould material that is usually used in Injection Moulding Industries. Following this, an experimental work was detailed relating to the use of ball nose end mill to machine hardened injection mould materials (up to 62 HRC).Surface roughness, surface topography and tool wear data were presented. The relationships of all these three properties respect to each other were also investigated. By machining these materials (Stavax, Stainless Steel, DF3 and XW5), a major wear occur on cutting tool which is called flank wear. Theflank wear is increased by increasing the hardness of the material used. This fact was supported by the result obtained, in which the surface roughness increases when the material hardness increased. Surface topography isdescribed through wavy marks and surface tearing. For 2 and 4-flute cutting tools, the waviness phenomenal ondecreases when material hardness was increased. Meanwhile, for surface tearing, the rate of occurrence is proportional to the increment of the material hardness.

Estimating the ice thickness of shallow glaciers from surface topography and mass-balance data with a shape optimization algorithm

A shape optimization algorithm is presented that estimates the ice thickness distribution within a three-dimensional, shallow glacier, given a transient surface geometry and a mass-balance distribution. The approach is based on the minimization of the surface topography misfit in the shallow ice approximation by means of a primal-dual procedure. The method׳s essential novelty is that it uses surface topography and mass-balance data only within the context of a time-dependent problem with evolving surface topography. Moreover, the algorithm is capable of computing some of the model parameters concurrently with the ice thickness distribution. The method is validated on synthetic and real-world data, where the choice of its Tikhonov regularization parameter by means of an L-curve criterion is discussed.

Effect of Two Different Energy Inputs for Laser Cladding of Stellite 6 on P91 and P22 Steel Substrates

Stellite 6 was deposited by laser cladding of two different chromium-bearing steel substrates (P91 and P22). The chemical compositions, microstructures and surface roughnesses of these coatings were characterized by atomic absorption spectroscopy, optical microscopy, scanning electron microscopy and atomic force microscopy. The microhardness of the coatings was measured and the wear mechanism of the coatings was examined using a pin-on-plate (reciprocating) wear testing machine. The results showed less cracking and pore development for Stellite 6 coatings applied to the P22 steel substrate. Further, the Stellite coating on P22 steel was significantly harder than that deposited on the P91 steel. The wear test results showed that the weight loss for the coating on P22 steel was significantly lower than for the P91 steel substrate. The surface topography data showed that the surface roughness for the coating on P22 steel was much lower than for the P91 steel substrate. It is concluded that the residual C content for the deposit on P22 was higher, mainly because the lower concentration of strong carbide formers, compared to P91, reduced the extent of carbon loss in the deposit.

Identification of individual features in areal surface topography data by means of template matching and the ring projection transform

Starting from areal surface topography data as provided by current commercial three-dimensional (3D) profilometers and 3D digital microscopes, this work investigates the problem of automatically identifying and extracting functionally relevant, individual features within the acquisition area. Feature identification is achieved by adopting an original template-matching algorithmic procedure, based on applying the ring projection transform in combination with a parametric template. The proposed algorithmic procedure addresses in particular template-matching scenarios where significant variability may be associated with the features to be compared to the reference template. The algorithm is applied to a test case involving the characterization of the surface texture of a superabrasive polishing tool used in hard-disk manufacturing.

Morphologic segmentation algorithms for extracting individual surface features from areal surface topography maps

Areal segmentation, i.e. the partitioning of areal surface topography data into regions, has recently attracted significant research interest in surface metrology. In particular morphologic segmentation, i.e. partitioning into Maxwellian hills and dales—currently the only segmentation approach endorsed by ISO specification standards—has shown potential for capturing the salient traits of a surface, so that its surface texture can be better encoded by parameters. However, recent developments in dimensional metrology applied to structured surfaces with features of dimensions on the order of micrometres (micro-electromechanical system, microfluidics, etc), and many other studies aimed at characterizing individual features in unstructured surfaces (scratches, bumps, holes, etc), are showing the importance of segmentation for extracting localized features from areal data. In this work, morphologic segmentation is applied to a selected set of case studies of industrial relevance, involving structured, semi-structured and unstructured surfaces, where the main goal is not the assessment of surface texture, but the extraction of individual surface features. The examples are designed to provide an overview of the main advantages and issues when applying morphologic segmentation in a comprehensive set of application scenarios.

Modeling of Microindentation with Consideration of the Surface Roughness

A finite element model of a microindentation is developed where the scanned surface topography data which represent the actual surface-roughness values are used in the construction of the finite element model of the workpiece. Indentation simulation with friction effect solely due to the surface deformation produces results which match the experimental ones in terms of residual indent size and pile-up heights. A roughness-dependent friction model is developed, which is comparable with the models proposed by Johnson (1985) and Alcala (2004).

Combined effect of tortuosity and surface roughness on estimation of flow rate through a single rough joint

Fluid flow through rock joints is greatly influenced by tortuosity and surface roughness, which cause a deviation from the cubic law of joint permeability. In this paper, in order to consider the combined effects of tortuosity and surface roughness on flow rate through a rough joint, a semi-empirical equation is first presented. In this equation, the impacts of tortuosity and surface roughness are represented by three quantitative parameters i.e., the tortuosity τ, surface tortuosity coefficient Ts and relative roughness Δ/2d, all of which can be computed based on surface topography data. Furthermore, the empirical constant A in the equation is determined according to the results of flow tests on three artificial joint specimens. Then the validity of the semi-empirical equation is confirmed by use of previously published experimental and numerical results. The obtained semi-empirical equation can predict the fluid flow rates through a rough joint well, and will be helpful to investigate the permeability of rock masses.

Developments in budget remote sensing for the geosciences

Acquiring outcrop, landform or other surface topography data in the field for the geosciences has always been challenging. Accessibility is often a problem, time is usually limited and an ideal spatial and temporal coverage often has to be compromised to be more manageable. However, emerging technologies, and some re‐inventions of rather older ones, can overcome many of these constraints in a very exciting and budget‐friendly manner. This article briefly introduces and reviews four major recent developments in budget remote sensing, specifically the use of blimps, kites, drones or UAVs (including quadcopters), and structure from motion (SFM) software. Both scientific and applied case studies are given and some possibilities for future studies are highlighted. Overall, the potential for these technologies to revolutionise the geosciences is clear and should be opportunistically embraced by scientists, resource and hazard managers and educators alike.

강릉항 완공 후 주변해역의 퇴적물 조직변수와 지형의 변화

To investigate the changes in depositional environment around Gangneung Harbor, we analyzed the surface sediment textural parameters and topography data collected five times from February 2007 to February 2009. In the study area, sediments were mainly composed of sand and its sediment size became finer at offshore sites. During summer time, however, the sand grains became coarser than winter season near Namhangjin Beach, inside the harbor, and offshore areas. On the other hand, the grain size of Anmok Beach showed a gradual finer trend with time. Compared with the previous studies conducted before the completion of Gangneung Harbor construction, the mean grain size became finer on Anmok Beach, while it was coarser on Namhangjin Beach. The bathymetric changes observed over a 2-year period showed predominant erosion in the area of 5 to 10 m water depths and deposition in 2 to 5 m water depths. The shallower area less than 2 m water depths showed an alternating trend and yet slightly more dominant erosion process. The sediment textural parameters and the distribution of erosion and deposition have changed continuously. Results imply that such changes show long-term trends as well as seasonal variations in which the trend may have been formed after the completion of Gangneung Harbor construction.

A Numerical Contact Model Based on Real Surface Topography

A numerical finite element contact model is developed to make use of the high precision surface topography data obtained at the nanoscale by atomic force microscopy or other imaging techniques while minimizing computational complexity. The model uses degrees of freedom that are normal to the surface, and uses the Boussinesq solution to relate the normal load to the long-range surface displacement response. The model for contact between two rough surfaces is developed in a step-by-step manner, taking into account the far-field effects of the loads developed at asperities that have come to contact in previous steps. Method accuracy is verified by comparison to simple test cases with well-defined analytical solutions. Agreement was found to be within 1 % for a wide range of practical loads for the high precision models. Applicability of extrapolation from lower precision models is presented. The real contact area estimates for micrometer-size tribology test machine surfaces are calculated and convergence behavior with mesh refinement is investigated.

Prediction of the internal structure of the sea floor and construction of a 3D model using the Markovian hypsotomography

Markovian hypsotomography is a new way to build a model of the internal structure of rock masses based on the processing of the earth’s surface topography data. The article demonstrates the opportunities for calculating the 3D velocity models and certain cross sections based on the example of the Caspian region.

The use of areal surface topography analysis for the inspection of micro-fabricated thin foil laser targets for ion acceleration

This paper proposes a novel approach to the characterization of critical dimensions and geometric form error at micro and sub-micrometric scales, suitable for application to micro-fabricated parts and devices. Thin foil laser targets for ion acceleration experiments are selected as the test subject in this instance. The approach is based on acquiring areal maps with a high-precision 3D optical interferometric profilometer and on processing the surface topography data with novel techniques obtained by merging knowledge and algorithms from surface metrology, dimensional metrology and computer vision/image processing for quality inspection. This new approach allows quantitative measurement results for the thin foil laser target to be obtained, and shows promise for being applied to a wide array of similar problems involving quality inspection of micro-parts and devices, and to structured surfaces in general.

GeoFlow: A novel model simulator for prediction of the 3‐D channeling flow in a rock fracture network

A fluid flow experiment was conducted on a granite sample containing two intersecting fractures. At constant confining pressure, water was supplied to the sample via a single inlet port, and the effluent was collected using four isolated outlet ports. The flow rate varied widely among these ports, indicating the formation of 3‐D preferential flow paths (channeling flow), which likely occur in fractured rocks but have been considerably difficult to identify by existing methods. The novel concept of GeoFlow, a discrete fracture network model simulator in which fractures have a heterogeneous aperture distribution, has been developed to analyze such complex fluid flow. A fluid flow simulation was conducted using GeoFlow with aperture distributions within the two fractures, as determined using fracture surface topography data. Despite the simplicity of the simulation, GeoFlow revealed a 3‐D channeling flow within the sample, which explains the general trend of the uneven outflows in the experiment.

Applying uncertainties to ocean colour data

Retrieval of operational optical products from the future Global Monitoring for Environment and Security (GMES) Sentinel-3 mission aims to provide continuity of existing missions delivering ocean/land colour, surface temperature and sea surface topography data. This paper describes the current status of the Sentinel-3 Level 2 Optical Prototype Processor (O-L2PP) whose development includes not only a list of products, but also associated uncertainty estimates—a key requirement for the processor. Examples of the approaches adopted within the Ocean and Land Colour Instrument (OLCI) processing module demonstrate how uncertainties can be estimated.

Automatic recognition of surface landmarks of anatomical structures of back and posture

Faulty postures, scoliosis and sagittal plane deformities should be detected as early as possible to apply preventive and treatment measures against major clinical consequences. To support documentation of the severity of deformity and diminish x-ray exposures, several solutions utilizing analysis of back surface topography data were introduced. A novel approach to automatic recognition and localization of anatomical landmarks of the human back is presented that may provide more repeatable results and speed up the whole procedure. The algorithm was designed as a two-step process involving a statistical model built upon expert knowledge and analysis of three-dimensional back surface shape data. Voronoi diagram is used to connect mean geometric relations, which provide a first approximation of the positions, with surface curvature distribution, which further guides the recognition process and gives final locations of landmarks. Positions obtained using the developed algorithms are validated with respect to accuracy of manual landmark indication by experts. Preliminary validation proved that the landmarks were localized correctly, with accuracy depending mostly on the characteristics of a given structure. It was concluded that recognition should mainly take into account the shape of the back surface, putting as little emphasis on the statistical approximation as possible.

Application of the BEM approach for a determination of the regional marine geoid model and the mean dynamic topography in the Southwest Pacific Ocean and Tasman Sea

Application of the BEM approach for a determination of the regional marine geoid model and the mean dynamic topography in the Southwest Pacific Ocean and Tasman SeaWe apply a novel approach for the gravimetric marine geoid modelling which utilise the boundary element method (BEM). The direct BEM formulation for the Laplace equation is applied to obtain a numerical solution to the linearised fixed gravimetric boundary-value problem in points at the Earth's surface. The numerical scheme uses the collocation method with linear basis functions. It involves a discretisation of the Earth's surface which is considered as a fixed boundary. The surface gravity disturbances represent the oblique derivative boundary condition. The BEM approach is applied to determine the marine geoid model over the study area of the Southwest Pacific Ocean and Tasman Sea using DNSC08 marine gravity data. The comparison of the BEM-derived and EGM2008 geoid models reveals that the geoid height differences vary within -25 and 18 cm with the standard deviation of 6 cm. The DNSC08 sea surface topography data and the new marine geoid are then used for modelling of the mean dynamic topography (MDT) over the study area. The local vertical datum (LVD) offsets estimated at 15 tide-gauge stations in New Zealand are finally used for testing the coastal MDT. The average value of differences between the MDT and LVD offsets is 1 cm.