The electrical properties of calcium sulfate rocks from decametric to micrometric scale
- Guinea, Ander, Playà, Elisabet, Rivero, Lluís, Ledo, Juan José, Queralt, Pilar
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Ledo, Juan José , Queralt, Pilar
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Applied Geophysics Vol. 85, no. (2012), p. 80-91
- Full Text:
- Reviewed:
- Description: Sulfate rocks have a sedimentary evaporitic origin and are present in many deposits worldwide. Among them, gypsum (dihydrated calcium sulfate) is the most common and is exploited for industrial purposes. Anhydrite (calcium sulfate) is frequently found in gypsum quarries and in non-outcropping sulfates. The greater hardness of anhydrite compared to gypsum causes a problem for gypsum extraction; quarry fronts have to be halted as soon as anhydrite is found. In this work the electrical properties of calcium sulfates have been studied by means of geoelectrical methods.A direct relationship between the electrical conductivity values of the calcium sulfate rocks and their lithological composition has been established with the lutitic matrix being the main controlling factor when it is well connected. When the matrix is under the percolation threshold the sulfate phases are dominant, and the electrical response of the rocks depends on the percentage of each phase. When the rock is matrix dominant, the electrical resistivity trend fits with the Hashin–Shtrikman lower bound for multiphase systems (considering gypsum, anhydrite and matrix as the components). On the other hand, when the rock is calcium sulfate dominant the trend shows the one of the Hashin–Shtrikman upper bound. The reference electrical resistivity value of pure anhydrite rocks has been defined as 104Ω·m and geoelectrical classification for calcium sulfate rocks has been elaborated. With this classification it is possible to differentiate between calcium sulfate rocks with different composition from their electrical resistivity value. This classification has been checked with field examples and calculating the theoretical resistivity value of thin section photographs with the program ELECFEM2D. The electrical behavior of calcium sulfate rocks is a good reference for other type of rocks with electrically differentiated components, and similar methods can be used to define their geoelectrical responses.
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Ledo, Juan José , Queralt, Pilar
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Applied Geophysics Vol. 85, no. (2012), p. 80-91
- Full Text:
- Reviewed:
- Description: Sulfate rocks have a sedimentary evaporitic origin and are present in many deposits worldwide. Among them, gypsum (dihydrated calcium sulfate) is the most common and is exploited for industrial purposes. Anhydrite (calcium sulfate) is frequently found in gypsum quarries and in non-outcropping sulfates. The greater hardness of anhydrite compared to gypsum causes a problem for gypsum extraction; quarry fronts have to be halted as soon as anhydrite is found. In this work the electrical properties of calcium sulfates have been studied by means of geoelectrical methods.A direct relationship between the electrical conductivity values of the calcium sulfate rocks and their lithological composition has been established with the lutitic matrix being the main controlling factor when it is well connected. When the matrix is under the percolation threshold the sulfate phases are dominant, and the electrical response of the rocks depends on the percentage of each phase. When the rock is matrix dominant, the electrical resistivity trend fits with the Hashin–Shtrikman lower bound for multiphase systems (considering gypsum, anhydrite and matrix as the components). On the other hand, when the rock is calcium sulfate dominant the trend shows the one of the Hashin–Shtrikman upper bound. The reference electrical resistivity value of pure anhydrite rocks has been defined as 104Ω·m and geoelectrical classification for calcium sulfate rocks has been elaborated. With this classification it is possible to differentiate between calcium sulfate rocks with different composition from their electrical resistivity value. This classification has been checked with field examples and calculating the theoretical resistivity value of thin section photographs with the program ELECFEM2D. The electrical behavior of calcium sulfate rocks is a good reference for other type of rocks with electrically differentiated components, and similar methods can be used to define their geoelectrical responses.
An assessment of a model-, grid-, and basin-independent tropical cyclone detection scheme in selected CMIP3 global climate models
- Tory, Kevin, Chand, Savin, Dare, Richard, McBride, John
- Authors: Tory, Kevin , Chand, Savin , Dare, Richard , McBride, John
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 26, no. 15 (2013), p. 5508-5522
- Full Text:
- Reviewed:
- Description: A novel tropical cyclone (TC) detection technique designed for coarse-resolution models is tested and evaluated. The detector, based on the Okubo-Weiss-Zeta parameter (OWZP), is applied to a selection of Coupled Model Intercomparison Project, phase 3 (CMIP3), models [Commonwealth Scientific and Industrial Research Organisation Mark, version 3.5 (CSIRO-Mk3.5); Max Planck Institute ECHAM5 (MPI-ECHAM5); and Geophysical Fluid Dynamics Laboratory Climate Model, versions 2.0 (GFDL CM2.0) and 2.1 (GFDL CM2.1)], and the combined performance of the model and detector is assessed by comparison with observed TC climatology for the period 1970-2000. Preliminary TC frequency projections are made using the three better-performing models by comparing the detected TC climatologies between the late twentieth and late twenty-first centuries. Very reasonable TC formation climatologies were detected in CSIRO-Mk3.5, MPI-ECHAM5, and GFDL CM2.1 for most basins, with the exception of the North Atlantic, where a large un-derdetection was present in all models. The GFDL CM2.0 model was excluded from the projection study because of a systematic underdetection in all basins. The above detection problems have been reported in other published studies, which suggests model rather than detector limitations are mostly responsible. This study demonstrates that coarse-resolution climate models do in general produce TC-like circulations with realistic geographical and seasonal distributions detectable by the OWZP TC detector. The preliminary projection results are consistent with the published literature, based on higher-resolution studies, of a global reductionofTCs between about6%and 20%, withamuch larger spread of results (about 120% to 250%) in individual basins. © 2013 American Meteorological Society.
- Authors: Tory, Kevin , Chand, Savin , Dare, Richard , McBride, John
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 26, no. 15 (2013), p. 5508-5522
- Full Text:
- Reviewed:
- Description: A novel tropical cyclone (TC) detection technique designed for coarse-resolution models is tested and evaluated. The detector, based on the Okubo-Weiss-Zeta parameter (OWZP), is applied to a selection of Coupled Model Intercomparison Project, phase 3 (CMIP3), models [Commonwealth Scientific and Industrial Research Organisation Mark, version 3.5 (CSIRO-Mk3.5); Max Planck Institute ECHAM5 (MPI-ECHAM5); and Geophysical Fluid Dynamics Laboratory Climate Model, versions 2.0 (GFDL CM2.0) and 2.1 (GFDL CM2.1)], and the combined performance of the model and detector is assessed by comparison with observed TC climatology for the period 1970-2000. Preliminary TC frequency projections are made using the three better-performing models by comparing the detected TC climatologies between the late twentieth and late twenty-first centuries. Very reasonable TC formation climatologies were detected in CSIRO-Mk3.5, MPI-ECHAM5, and GFDL CM2.1 for most basins, with the exception of the North Atlantic, where a large un-derdetection was present in all models. The GFDL CM2.0 model was excluded from the projection study because of a systematic underdetection in all basins. The above detection problems have been reported in other published studies, which suggests model rather than detector limitations are mostly responsible. This study demonstrates that coarse-resolution climate models do in general produce TC-like circulations with realistic geographical and seasonal distributions detectable by the OWZP TC detector. The preliminary projection results are consistent with the published literature, based on higher-resolution studies, of a global reductionofTCs between about6%and 20%, withamuch larger spread of results (about 120% to 250%) in individual basins. © 2013 American Meteorological Society.
Using point cloud data to identify, trace, and regularize the outlines of buildings
- Authors: Awrangjeb, Mohammad
- Date: 2016
- Type: Text , Journal article
- Relation: International Journal of Remote Sensing Vol. 37, no. 3 (2016), p. 551-579
- Full Text:
- Reviewed:
- Description: Rectilinear building outline generation from the point set of a building usually works in three steps. Boundary edges that constitute the building outline are first identified. A sequence of points is then traced from the edges to define the building boundary. Finally, lines are generated from the sequence of points and adjusted to form a regular building outline. Existing solutions have shortcomings in one or more of the following cases: identifying details along a concave shape, separate identification of a 'hole' inside the shape, proper boundary tracing, and preservation of detailed information along a regularized building outline. This article proposes new solutions to all three steps. By using the maximum point-to-point distance in the input data, the solution to the identification step properly detects the boundary edges for any type of shape and separately recognizes holes, if any, inside the shape. The proposed tracing algorithm divides boundary edges into segments, accurately obtains the sequence of points for each segment and then merges them, if necessary, to produce a single boundary for each shape. The regularization step proposes an improved corner and line extraction algorithm and adjusts the extracted lines with respect to the automatically determined principal directions of buildings. In order to evaluate the performance, an evaluation system that makes corner correspondences between an extracted building outline and its reference outline is also proposed. Experimental results show that the proposed solutions can preserve detail along the building boundary and offer high pixel-based completeness and geometric accuracy, even in low-density input data. © 2016 The Author(s). Published by Taylor & Francis.
- Description: Rectilinear building outline generation from the point set of a building usually works in three steps. Boundary edges that constitute the building outline are first identified. A sequence of points is then traced from the edges to define the building boundary. Finally, lines are generated from the sequence of points and adjusted to form a regular building outline. Existing solutions have shortcomings in one or more of the following cases: identifying details along a concave shape, separate identification of a ‘hole’ inside the shape, proper boundary tracing, and preservation of detailed information along a regularized building outline. This article proposes new solutions to all three steps. By using the maximum point-to-point distance in the input data, the solution to the identification step properly detects the boundary edges for any type of shape and separately recognizes holes, if any, inside the shape. The proposed tracing algorithm divides boundary edges into segments, accurately obtains the sequence of points for each segment and then merges them, if necessary, to produce a single boundary for each shape. The regularization step proposes an improved corner and line extraction algorithm and adjusts the extracted lines with respect to the automatically determined principal directions of buildings. In order to evaluate the performance, an evaluation system that makes corner correspondences between an extracted building outline and its reference outline is also proposed. Experimental results show that the proposed solutions can preserve detail along the building boundary and offer high pixel-based completeness and geometric accuracy, even in low-density input data. © 2016 The Author(s). Published by Taylor & Francis.
- Authors: Awrangjeb, Mohammad
- Date: 2016
- Type: Text , Journal article
- Relation: International Journal of Remote Sensing Vol. 37, no. 3 (2016), p. 551-579
- Full Text:
- Reviewed:
- Description: Rectilinear building outline generation from the point set of a building usually works in three steps. Boundary edges that constitute the building outline are first identified. A sequence of points is then traced from the edges to define the building boundary. Finally, lines are generated from the sequence of points and adjusted to form a regular building outline. Existing solutions have shortcomings in one or more of the following cases: identifying details along a concave shape, separate identification of a 'hole' inside the shape, proper boundary tracing, and preservation of detailed information along a regularized building outline. This article proposes new solutions to all three steps. By using the maximum point-to-point distance in the input data, the solution to the identification step properly detects the boundary edges for any type of shape and separately recognizes holes, if any, inside the shape. The proposed tracing algorithm divides boundary edges into segments, accurately obtains the sequence of points for each segment and then merges them, if necessary, to produce a single boundary for each shape. The regularization step proposes an improved corner and line extraction algorithm and adjusts the extracted lines with respect to the automatically determined principal directions of buildings. In order to evaluate the performance, an evaluation system that makes corner correspondences between an extracted building outline and its reference outline is also proposed. Experimental results show that the proposed solutions can preserve detail along the building boundary and offer high pixel-based completeness and geometric accuracy, even in low-density input data. © 2016 The Author(s). Published by Taylor & Francis.
- Description: Rectilinear building outline generation from the point set of a building usually works in three steps. Boundary edges that constitute the building outline are first identified. A sequence of points is then traced from the edges to define the building boundary. Finally, lines are generated from the sequence of points and adjusted to form a regular building outline. Existing solutions have shortcomings in one or more of the following cases: identifying details along a concave shape, separate identification of a ‘hole’ inside the shape, proper boundary tracing, and preservation of detailed information along a regularized building outline. This article proposes new solutions to all three steps. By using the maximum point-to-point distance in the input data, the solution to the identification step properly detects the boundary edges for any type of shape and separately recognizes holes, if any, inside the shape. The proposed tracing algorithm divides boundary edges into segments, accurately obtains the sequence of points for each segment and then merges them, if necessary, to produce a single boundary for each shape. The regularization step proposes an improved corner and line extraction algorithm and adjusts the extracted lines with respect to the automatically determined principal directions of buildings. In order to evaluate the performance, an evaluation system that makes corner correspondences between an extracted building outline and its reference outline is also proposed. Experimental results show that the proposed solutions can preserve detail along the building boundary and offer high pixel-based completeness and geometric accuracy, even in low-density input data. © 2016 The Author(s). Published by Taylor & Francis.
Land rebound after banning deep groundwater extraction in Changzhou, China
- Wang, Guang-ya, Zhu, Jin-qi, You, Greg, Yu, Jun, Gong, Xu-long, Li, Wei, Gou, Fu-gang
- Authors: Wang, Guang-ya , Zhu, Jin-qi , You, Greg , Yu, Jun , Gong, Xu-long , Li, Wei , Gou, Fu-gang
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 229, no. (2017), p. 13-20
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- Reviewed:
- Description: More than 30 years groundwater overdraft had resulted in hydraulic head declined from near the ground surface to 85 m deep in the second confined aquifer (CA2) in Changzhou, and lead to regional land subsidence from 1970's to early 2000's. After banning deep groundwater extraction was banned in 2000, the hydraulic head of CA2 had recovered to 37.6 m in Changzhou by the end of 2013. Based on several stages first and second order leveling results and long term monitoring data from the multi-strata borehole extensometer station (BES), it was revealed that the land subsidence is attributed to the compression of both aquifers and aquitards in the porous aquifer system. The spatial characteristics of subsidence are related not only to hydraulic head pattern in the area, but also to the thickness and compressibility of different soil strata, and distance from the aquifer. Since banning deep groundwater extraction, the ground uplifted 37.22 mm (5.4% of the pre subsidence) at BES, Changzhou due to the hydraulic head recovering. Strata compression and rebound was recorded as: the upper most stratum, and the underlying aquitard of CA2, and the upper CA3 are still in the compression process, the lower CA3 layer and the upper most segment of aquitard of CA2 rebounded about 90% of the pre compression recorded since 1984, and the CA2 and its adjacent overlying aquitard rebounded 3.8%–9.7% of the pre compression. © 2017 Elsevier B.V.
- Authors: Wang, Guang-ya , Zhu, Jin-qi , You, Greg , Yu, Jun , Gong, Xu-long , Li, Wei , Gou, Fu-gang
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 229, no. (2017), p. 13-20
- Full Text:
- Reviewed:
- Description: More than 30 years groundwater overdraft had resulted in hydraulic head declined from near the ground surface to 85 m deep in the second confined aquifer (CA2) in Changzhou, and lead to regional land subsidence from 1970's to early 2000's. After banning deep groundwater extraction was banned in 2000, the hydraulic head of CA2 had recovered to 37.6 m in Changzhou by the end of 2013. Based on several stages first and second order leveling results and long term monitoring data from the multi-strata borehole extensometer station (BES), it was revealed that the land subsidence is attributed to the compression of both aquifers and aquitards in the porous aquifer system. The spatial characteristics of subsidence are related not only to hydraulic head pattern in the area, but also to the thickness and compressibility of different soil strata, and distance from the aquifer. Since banning deep groundwater extraction, the ground uplifted 37.22 mm (5.4% of the pre subsidence) at BES, Changzhou due to the hydraulic head recovering. Strata compression and rebound was recorded as: the upper most stratum, and the underlying aquitard of CA2, and the upper CA3 are still in the compression process, the lower CA3 layer and the upper most segment of aquitard of CA2 rebounded about 90% of the pre compression recorded since 1984, and the CA2 and its adjacent overlying aquitard rebounded 3.8%–9.7% of the pre compression. © 2017 Elsevier B.V.
A statistical assessment of Southern Hemisphere tropical cyclone tracks in climate models
- Ramsay, Hamish, Chand, Savin, Camargo, Suzana
- Authors: Ramsay, Hamish , Chand, Savin , Camargo, Suzana
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 24 (2018), p. 10081-10104
- Full Text:
- Reviewed:
- Description: Reliable projections of future changes in tropical cyclone (TC) characteristics are highly dependent on the ability of global climate models (GCMs) to simulate the observed characteristics of TCs (i.e., their frequency, genesis locations, movement, and intensity). Here, we investigate the performance of a suite of GCMs from the U.S. CLIVAR Working Group on Hurricanes in simulating observed climatological features of TCs in the Southern Hemisphere. A subset of these GCMs is also explored under three idealized warming scenarios. Two types of simulated TC tracks are evaluated on the basis of a commonly applied cluster analysis: 1) explicitly simulated tracks, and 2) downscaled tracks, derived from a statistical-dynamical technique that depends on the models' large-scale environmental fields. Climatological TC properties such as genesis locations, annual frequency, lifetime maximum intensity (LMI), and seasonality are evaluated for both track types. Future changes to annual frequency, LMI, and the latitude of LMI are evaluated using the downscaled tracks where large sample sizes allow for statistically robust results. An ensemble approach is used to assess future changes of explicit tracks owing to their small number of realizations. We show that the downscaled tracks generally outperform the explicit tracks in relation to many of the climatological features of Southern Hemisphere TCs, despite a few notable biases. Future changes to the frequency and intensity of TCs in the downscaled simulations are found to be highly dependent on the warming scenario and model, with the most robust result being an increase in the LMI under a uniform 2°C surface warming.
- Authors: Ramsay, Hamish , Chand, Savin , Camargo, Suzana
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 24 (2018), p. 10081-10104
- Full Text:
- Reviewed:
- Description: Reliable projections of future changes in tropical cyclone (TC) characteristics are highly dependent on the ability of global climate models (GCMs) to simulate the observed characteristics of TCs (i.e., their frequency, genesis locations, movement, and intensity). Here, we investigate the performance of a suite of GCMs from the U.S. CLIVAR Working Group on Hurricanes in simulating observed climatological features of TCs in the Southern Hemisphere. A subset of these GCMs is also explored under three idealized warming scenarios. Two types of simulated TC tracks are evaluated on the basis of a commonly applied cluster analysis: 1) explicitly simulated tracks, and 2) downscaled tracks, derived from a statistical-dynamical technique that depends on the models' large-scale environmental fields. Climatological TC properties such as genesis locations, annual frequency, lifetime maximum intensity (LMI), and seasonality are evaluated for both track types. Future changes to annual frequency, LMI, and the latitude of LMI are evaluated using the downscaled tracks where large sample sizes allow for statistically robust results. An ensemble approach is used to assess future changes of explicit tracks owing to their small number of realizations. We show that the downscaled tracks generally outperform the explicit tracks in relation to many of the climatological features of Southern Hemisphere TCs, despite a few notable biases. Future changes to the frequency and intensity of TCs in the downscaled simulations are found to be highly dependent on the warming scenario and model, with the most robust result being an increase in the LMI under a uniform 2°C surface warming.
Segmentation of airborne point cloud data for automatic building roof extraction
- Gilani, Syed, Awrangjeb, Mohammad, Lu, Guojun
- Authors: Gilani, Syed , Awrangjeb, Mohammad , Lu, Guojun
- Date: 2018
- Type: Text , Journal article
- Relation: GIScience & Remote Sensing Vol. 55, no. 1 (2018), p. 63-89
- Full Text:
- Reviewed:
- Description: Roof plane segmentation is a complex task since point cloud data carry no connection information and do not provide any semantic characteristics of the underlying scanned surfaces. Point cloud density, complex roof profiles, and occlusion add another layer of complexity which often encounter in practice. In this article, we present a new technique that provides a better interpolation of roof regions where multiple surfaces intersect creating non-manifold points. As a result, these geometric features are preserved to achieve automated identification and segmentation of the roof planes from unstructured laser data. The proposed technique has been tested using the International Society for Photogrammetry and Remote Sensing benchmark and three Australian datasets, which differ in terrain, point density, building sizes, and vegetation. The qualitative and quantitative results show the robustness of the methodology and indicate that the proposed technique can eliminate vegetation and extract buildings as well as their non-occluding parts from the complex scenes at a high success rate for building detection (between 83.9% and 100% per-object completeness) and roof plane extraction (between 73.9% and 96% per-object completeness). The proposed method works more robustly than some existing methods in the presence of occlusion and low point sampling as indicated by the correctness of above 95% for all the datasets.
- Authors: Gilani, Syed , Awrangjeb, Mohammad , Lu, Guojun
- Date: 2018
- Type: Text , Journal article
- Relation: GIScience & Remote Sensing Vol. 55, no. 1 (2018), p. 63-89
- Full Text:
- Reviewed:
- Description: Roof plane segmentation is a complex task since point cloud data carry no connection information and do not provide any semantic characteristics of the underlying scanned surfaces. Point cloud density, complex roof profiles, and occlusion add another layer of complexity which often encounter in practice. In this article, we present a new technique that provides a better interpolation of roof regions where multiple surfaces intersect creating non-manifold points. As a result, these geometric features are preserved to achieve automated identification and segmentation of the roof planes from unstructured laser data. The proposed technique has been tested using the International Society for Photogrammetry and Remote Sensing benchmark and three Australian datasets, which differ in terrain, point density, building sizes, and vegetation. The qualitative and quantitative results show the robustness of the methodology and indicate that the proposed technique can eliminate vegetation and extract buildings as well as their non-occluding parts from the complex scenes at a high success rate for building detection (between 83.9% and 100% per-object completeness) and roof plane extraction (between 73.9% and 96% per-object completeness). The proposed method works more robustly than some existing methods in the presence of occlusion and low point sampling as indicated by the correctness of above 95% for all the datasets.
Statistical assessment of the OWZ Tropical Cyclone Tracking Scheme in ERA-Interim
- Bell, Samuel, Chand, Savin, Tory, Kevin, Turville, Christopher
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Turville, Christopher
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 6 (2018), p. 2217-2232
- Full Text:
- Reviewed:
- Description: The Okubo–Weiss–Zeta (OWZ) tropical cyclone (TC) detection scheme, which has been used to detect TCs in climate, seasonal prediction, and weather forecast models, is assessed on its ability to produce a realistic TC track climatology in the ERA-Interim product over the 25-yr period 1989 to 2013. The analysis focuses on TCs that achieve gale-force (17ms21) sustained winds. Objective criteria were established to define TC tracks once they reach gale force for both observed and detected TCs. A lack of consistency between storm tracks preceding this level of intensity led these track segments to be removed from the analysis.Asubtropical jet (STJ) diagnostic is used to terminate transitioning TCs and is found to be preferable to a fixed latitude cutoff point. TC tracks were analyzed across seven TC basins, using a probabilistic clustering technique that is based on regression mixture models. The technique grouped TC tracks together based on their geographical location and shape of trajectory in five separate ‘‘cluster regions’’ around the globe. A mean trajectory was then regressed for each cluster that showed good agreement between the detected and observed tracks. Other track measures such as interannual TC days and translational speeds were also replicated to a satisfactory level, with TC days showing limited sensitivity to different latitude cutoff points. Successful validation in reanalysis data allows this model- and grid-resolution-independent TC tracking scheme to be applied to climate models with confidence in its ability to identify TC tracks in coarse-resolution climate models.
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Turville, Christopher
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 6 (2018), p. 2217-2232
- Full Text:
- Reviewed:
- Description: The Okubo–Weiss–Zeta (OWZ) tropical cyclone (TC) detection scheme, which has been used to detect TCs in climate, seasonal prediction, and weather forecast models, is assessed on its ability to produce a realistic TC track climatology in the ERA-Interim product over the 25-yr period 1989 to 2013. The analysis focuses on TCs that achieve gale-force (17ms21) sustained winds. Objective criteria were established to define TC tracks once they reach gale force for both observed and detected TCs. A lack of consistency between storm tracks preceding this level of intensity led these track segments to be removed from the analysis.Asubtropical jet (STJ) diagnostic is used to terminate transitioning TCs and is found to be preferable to a fixed latitude cutoff point. TC tracks were analyzed across seven TC basins, using a probabilistic clustering technique that is based on regression mixture models. The technique grouped TC tracks together based on their geographical location and shape of trajectory in five separate ‘‘cluster regions’’ around the globe. A mean trajectory was then regressed for each cluster that showed good agreement between the detected and observed tracks. Other track measures such as interannual TC days and translational speeds were also replicated to a satisfactory level, with TC days showing limited sensitivity to different latitude cutoff points. Successful validation in reanalysis data allows this model- and grid-resolution-independent TC tracking scheme to be applied to climate models with confidence in its ability to identify TC tracks in coarse-resolution climate models.
Western north pacific tropical cyclone tracks in cmip5 models : statistical assessment using a model-independent detection and tracking scheme
- Bell, Samuel, Chand, Savin, Camargo, Suzana, Tory, Kevin, Turville, Chris, Ye, Harvey
- Authors: Bell, Samuel , Chand, Savin , Camargo, Suzana , Tory, Kevin , Turville, Chris , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 32, no. 21 (2019), p. 7191-7208
- Full Text:
- Reviewed:
- Description: Past studies have shown that tropical cyclone (TC) projection results can be sensitive to different types of TC tracking schemes, and that the relative adjustments of detection criteria to accommodate different models may not necessarily provide a consistent platform for comparison of projection results. Here, future climate projections of TC activity in the western North Pacific basin (WNP, defined from 0°-50°NAND 100°E-180°) are assessed with a model-independent detection and tracking scheme. This scheme is applied to models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) forced under the historical and representative concentration pathway 8.5 (RCP8.5) conditions. TC tracks from the observed records and independent models are analyzed simultaneously with a curve-clustering algorithm, allowing observed and model tracks to be projected onto the same set of clusters (k =9). Four of the nine clusters were projected to undergo significant changes in TC frequency. Straight-moving TCs in the South China Sea were projected to significantly decrease. Projected increases in TC frequency were found poleward of 20°N and east of 160°E, consistent with changes in ascending motion, as well as vertical wind shear and relative humidity respectively. Projections of TC track exposure indicated significant reductions for southern China and the Philippines and significant increases for the Korean peninsula and Japan, although very few model TCs reached the latter subtropical regions in comparison to the observations. The use of a fundamentally different detection methodology that overcomes the detector/tracker bias gives increased certainty to projections as best as lowresolution simulations can offer. © 2019 American Meteorological Society.
- Authors: Bell, Samuel , Chand, Savin , Camargo, Suzana , Tory, Kevin , Turville, Chris , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 32, no. 21 (2019), p. 7191-7208
- Full Text:
- Reviewed:
- Description: Past studies have shown that tropical cyclone (TC) projection results can be sensitive to different types of TC tracking schemes, and that the relative adjustments of detection criteria to accommodate different models may not necessarily provide a consistent platform for comparison of projection results. Here, future climate projections of TC activity in the western North Pacific basin (WNP, defined from 0°-50°NAND 100°E-180°) are assessed with a model-independent detection and tracking scheme. This scheme is applied to models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) forced under the historical and representative concentration pathway 8.5 (RCP8.5) conditions. TC tracks from the observed records and independent models are analyzed simultaneously with a curve-clustering algorithm, allowing observed and model tracks to be projected onto the same set of clusters (k =9). Four of the nine clusters were projected to undergo significant changes in TC frequency. Straight-moving TCs in the South China Sea were projected to significantly decrease. Projected increases in TC frequency were found poleward of 20°N and east of 160°E, consistent with changes in ascending motion, as well as vertical wind shear and relative humidity respectively. Projections of TC track exposure indicated significant reductions for southern China and the Philippines and significant increases for the Korean peninsula and Japan, although very few model TCs reached the latter subtropical regions in comparison to the observations. The use of a fundamentally different detection methodology that overcomes the detector/tracker bias gives increased certainty to projections as best as lowresolution simulations can offer. © 2019 American Meteorological Society.
Effect of negative excess pore-water pressure on the stability of excavated slopes
- Ghadrdan, Mohsen, Shaghaghi, Tahereh, Tolooiyan, Ali
- Authors: Ghadrdan, Mohsen , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geotechnique Letters Vol. 10, no. 1 (Mar 2020), p. 20-29
- Full Text:
- Reviewed:
- Description: Generation of negative excess pore-water pressure (NEPWP) due to the excavation of saturated soils under undrained conditions and the dissipation that follows over time may result in different short- and long-term slope instability. The NEPWP generated due to excavation gradually decreases towards equilibrium or, in some cases, steady seepage. Hence, total pore-water pressures immediately after excavation are lower than the ultimate equilibrium values, leading to a reduction of the average effective stresses in the slope and subsequently threatening stability in the long term. In this research study, the stability of three benchmark civil and mining excavations has been studied, considering the effects of the generation and dissipation of NEPWP. A series of numerical simulations are conducted to determine the role of in situ stresses and time in NEPWP dissipation as well as the consequent effects on the stability of the excavated slopes. To conduct a realistic time-dependent transient analysis, fully coupled hydro-geomechanical formulation has been employed. Results show that in general, higher removal of stress levels lead to higher NEPWP generation and higher factor of safety values in the short term. Thereafter, the dissipation of NEPWP threatens the long-term stability of the excavation.
- Authors: Ghadrdan, Mohsen , Shaghaghi, Tahereh , Tolooiyan, Ali
- Date: 2020
- Type: Text , Journal article
- Relation: Geotechnique Letters Vol. 10, no. 1 (Mar 2020), p. 20-29
- Full Text:
- Reviewed:
- Description: Generation of negative excess pore-water pressure (NEPWP) due to the excavation of saturated soils under undrained conditions and the dissipation that follows over time may result in different short- and long-term slope instability. The NEPWP generated due to excavation gradually decreases towards equilibrium or, in some cases, steady seepage. Hence, total pore-water pressures immediately after excavation are lower than the ultimate equilibrium values, leading to a reduction of the average effective stresses in the slope and subsequently threatening stability in the long term. In this research study, the stability of three benchmark civil and mining excavations has been studied, considering the effects of the generation and dissipation of NEPWP. A series of numerical simulations are conducted to determine the role of in situ stresses and time in NEPWP dissipation as well as the consequent effects on the stability of the excavated slopes. To conduct a realistic time-dependent transient analysis, fully coupled hydro-geomechanical formulation has been employed. Results show that in general, higher removal of stress levels lead to higher NEPWP generation and higher factor of safety values in the short term. Thereafter, the dissipation of NEPWP threatens the long-term stability of the excavation.
Naturally occurring potentially harmful elements in groundwater in makueni county, south‐eastern kenya : effects on drinking water quality and agriculture
- Gevera, Patrick, Cave, Mark, Dowling, Kim, Gikuma‐njuru, Peter, Mouri, Hassina
- Authors: Gevera, Patrick , Cave, Mark , Dowling, Kim , Gikuma‐njuru, Peter , Mouri, Hassina
- Date: 2020
- Type: Text , Journal article
- Relation: Geosciences (Switzerland) Vol. 10, no. 2 (2020), p.
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- Description: Makueni County is located in the semi‐arid south‐eastern Kenya region characterized by unreliable rainfall and limited surface water resources. This necessitates a high reliance on groundwater for domestic and agricultural use. In this paper, we report on the physico‐chemical characteristics of 20 drinking water sources (boreholes, shallow wells, streams, and tap water) collected during the dry season (November 2018), the geochemical processes controlling their composition, and their suitability for drinking water and irrigation. Of all the physico‐chemical parameters analysed, the concentrations of total dissolved solids, hardness, electrical conductivity, magnesium, calcium, chloride, and fluoride exceeded the permissible drinking water limits set by both the World Health Organization (WHO) and Kenya Bureau of Standards (KEBS) in up to 55% of the samples. The dominant ions reflect the high salinity in the water that ranged from very high to extreme in up to 50% of samples. The northern region shows the highest concentrations of the dominant parameters. The water type is predominantly Ca‐Mg‐HCO3 with a trend to Ca‐Mg‐Cl‐ SO4. Rock weathering and evaporation are suggested to be the primary controls of groundwater geochemical characteristics. High salinity and fluoride, which are associated with reported undesirable taste and gastrointestinal upsets, as well as cases of dental fluorosis are some of the effects of consuming groundwater in the region. These two parameters can be attributed to the weathering of biotite gneisses, granitoid gneisses, migmatites, and basaltic rocks that occur in the area. The high salinity and alkalinity of most of the samples analysed, renders the water unsuitable for irrigation in the study area. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- Authors: Gevera, Patrick , Cave, Mark , Dowling, Kim , Gikuma‐njuru, Peter , Mouri, Hassina
- Date: 2020
- Type: Text , Journal article
- Relation: Geosciences (Switzerland) Vol. 10, no. 2 (2020), p.
- Full Text:
- Reviewed:
- Description: Makueni County is located in the semi‐arid south‐eastern Kenya region characterized by unreliable rainfall and limited surface water resources. This necessitates a high reliance on groundwater for domestic and agricultural use. In this paper, we report on the physico‐chemical characteristics of 20 drinking water sources (boreholes, shallow wells, streams, and tap water) collected during the dry season (November 2018), the geochemical processes controlling their composition, and their suitability for drinking water and irrigation. Of all the physico‐chemical parameters analysed, the concentrations of total dissolved solids, hardness, electrical conductivity, magnesium, calcium, chloride, and fluoride exceeded the permissible drinking water limits set by both the World Health Organization (WHO) and Kenya Bureau of Standards (KEBS) in up to 55% of the samples. The dominant ions reflect the high salinity in the water that ranged from very high to extreme in up to 50% of samples. The northern region shows the highest concentrations of the dominant parameters. The water type is predominantly Ca‐Mg‐HCO3 with a trend to Ca‐Mg‐Cl‐ SO4. Rock weathering and evaporation are suggested to be the primary controls of groundwater geochemical characteristics. High salinity and fluoride, which are associated with reported undesirable taste and gastrointestinal upsets, as well as cases of dental fluorosis are some of the effects of consuming groundwater in the region. These two parameters can be attributed to the weathering of biotite gneisses, granitoid gneisses, migmatites, and basaltic rocks that occur in the area. The high salinity and alkalinity of most of the samples analysed, renders the water unsuitable for irrigation in the study area. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
Reappraisal of the astm/aashto standard rolling device method for plastic limit determination of fine-grained soils
- Soltani, Amin, O’Kelly, Brendan
- Authors: Soltani, Amin , O’Kelly, Brendan
- Date: 2021
- Type: Text , Journal article
- Relation: Geosciences (Switzerland) Vol. 11, no. 6 (2021), p.
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- Description: Given its apparent limitations, various attempts have been made to develop alternative testing approaches to the standardized rolling-thread plastic limit (PLRT) method (for fine-grained soils), targeting higher degrees of repeatability and reproducibility. Among these, device-rolling techniques, including the method described in ASTM D4318/AASHTO T90 standards, based on original work by Bobrowski and Griekspoor (BG) and which follows the same basic principles as the standard thread-rolling (by hand) test, have been highly underrated by some researchers. To better understand the true potentials and/or limitations of the BG method for soil plasticity determination (i.e., PLBG), this paper presents a critical reappraisal of the PLRT–PLBG relationship using a comprehensive statistical analysis performed on a large and diverse database of 60 PLRT– PLBG test pairs. It is demonstrated that for a given fine-grained soil, the BG and RT methods produce essentially similar PL values. The 95% lower and upper (water content) statistical agreement limits between PLBG and PLRT were, respectively, obtained as −5.03% and +4.51%, and both deemed “statistically insignificant” when compared to the inductively-defined reference limit of ±8% (i.e., the highest possible difference in PLRT based on its repeatability, as reported in the literature). Furthermore, the likelihoods of PLBG underestimating and overestimating PLRT were 50% and 40%, respectively; debunking the notion presented by some researchers that the BG method generally tends to greatly underestimate PLRT. It is also shown that the degree of underestimation/overestimation does not systematically change with changes in basic soil properties; suggesting that the differences between PLBG and PLRT are most likely random in nature. Compared to PLRT, the likelihood of achieving consistent soil classifications employing PLBG (along with the liquid limit) was shown to be 98%, with the identified discrepancies being cases that plot relatively close to the A-Line. As such, PLBG can be used with confidence for soil classification purposes. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
- Authors: Soltani, Amin , O’Kelly, Brendan
- Date: 2021
- Type: Text , Journal article
- Relation: Geosciences (Switzerland) Vol. 11, no. 6 (2021), p.
- Full Text:
- Reviewed:
- Description: Given its apparent limitations, various attempts have been made to develop alternative testing approaches to the standardized rolling-thread plastic limit (PLRT) method (for fine-grained soils), targeting higher degrees of repeatability and reproducibility. Among these, device-rolling techniques, including the method described in ASTM D4318/AASHTO T90 standards, based on original work by Bobrowski and Griekspoor (BG) and which follows the same basic principles as the standard thread-rolling (by hand) test, have been highly underrated by some researchers. To better understand the true potentials and/or limitations of the BG method for soil plasticity determination (i.e., PLBG), this paper presents a critical reappraisal of the PLRT–PLBG relationship using a comprehensive statistical analysis performed on a large and diverse database of 60 PLRT– PLBG test pairs. It is demonstrated that for a given fine-grained soil, the BG and RT methods produce essentially similar PL values. The 95% lower and upper (water content) statistical agreement limits between PLBG and PLRT were, respectively, obtained as −5.03% and +4.51%, and both deemed “statistically insignificant” when compared to the inductively-defined reference limit of ±8% (i.e., the highest possible difference in PLRT based on its repeatability, as reported in the literature). Furthermore, the likelihoods of PLBG underestimating and overestimating PLRT were 50% and 40%, respectively; debunking the notion presented by some researchers that the BG method generally tends to greatly underestimate PLRT. It is also shown that the degree of underestimation/overestimation does not systematically change with changes in basic soil properties; suggesting that the differences between PLBG and PLRT are most likely random in nature. Compared to PLRT, the likelihood of achieving consistent soil classifications employing PLBG (along with the liquid limit) was shown to be 98%, with the identified discrepancies being cases that plot relatively close to the A-Line. As such, PLBG can be used with confidence for soil classification purposes. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
Using vector agents to implement an unsupervised image classification algorithm
- Borna, Kambiz, Moore, Antoni, Hoshyar, Azadeh, Sirguey, Pascal
- Authors: Borna, Kambiz , Moore, Antoni , Hoshyar, Azadeh , Sirguey, Pascal
- Date: 2021
- Type: Text , Journal article
- Relation: Remote Sensing Vol. 13, no. 23 (2021), p.
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- Description: Unsupervised image classification methods conventionally use the spatial information of pixels to reduce the effect of speckled noise in the classified map. To extract this spatial information, they employ a predefined geometry, i.e., a fixed-size window or segmentation map. However, this coding of geometry lacks the necessary complexity to accurately reflect the spatial connectivity within objects in a scene. Additionally, there is no unique mathematical formula to determine the shape and scale applied to the geometry, being parameters that are usually estimated by expert users. In this paper, a novel geometry-led approach using Vector Agents (VAs) is proposed to address the above drawbacks in unsupervised classification algorithms. Our proposed method has two primary steps: (1) creating reliable training samples and (2) constructing the VA model. In the first step, the method applies the statistical information of a classified image by k-means to select a set of reliable training samples. Then, in the second step, the VAs are trained and constructed to classify the image. The model is tested for classification on three high spatial resolution images. The results show the enhanced capability of the VA model to reduce noise in images that have complex features, e.g., streets, buildings. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
- Authors: Borna, Kambiz , Moore, Antoni , Hoshyar, Azadeh , Sirguey, Pascal
- Date: 2021
- Type: Text , Journal article
- Relation: Remote Sensing Vol. 13, no. 23 (2021), p.
- Full Text:
- Reviewed:
- Description: Unsupervised image classification methods conventionally use the spatial information of pixels to reduce the effect of speckled noise in the classified map. To extract this spatial information, they employ a predefined geometry, i.e., a fixed-size window or segmentation map. However, this coding of geometry lacks the necessary complexity to accurately reflect the spatial connectivity within objects in a scene. Additionally, there is no unique mathematical formula to determine the shape and scale applied to the geometry, being parameters that are usually estimated by expert users. In this paper, a novel geometry-led approach using Vector Agents (VAs) is proposed to address the above drawbacks in unsupervised classification algorithms. Our proposed method has two primary steps: (1) creating reliable training samples and (2) constructing the VA model. In the first step, the method applies the statistical information of a classified image by k-means to select a set of reliable training samples. Then, in the second step, the VAs are trained and constructed to classify the image. The model is tested for classification on three high spatial resolution images. The results show the enhanced capability of the VA model to reduce noise in images that have complex features, e.g., streets, buildings. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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