Rugged Topography Research Articles

Accuracy assessment of the CARTOSAT DEM using robust statistical measures

CARTOSAT-1-derived 10 m spatial resolution digital elevation model (DEM) for entire India was compiled for several applications. Overall assessment of the accuracy of this product requires additional regional studies involving ground truth control points and accuracy verification methods with a higher level of precision, such as the global positioning system (GPS).The study presented in this paper compares the accuracy of CARTOSAT-1 datasets with respect to eight sites over different terrains in India with the same GPS system. Robust statistical analysis including mean errors, standard deviation error, root mean square error (RMSE), skewness, kurtosis measures and Shapiro–Wilk’s normality test were used for evaluating error. The results of this study show a linear trend between the DEM and the ground control points (GCP). The mean error is very high in highlands ranging up to − 14.06 m, whereas in moderate terrain it ranges around 2.65 m and in the lowland about 1.20 m. RMSE ranges up to 28.82 m in rugged high-altitude topographies, 6.24 m in moderate and 1.98 m in low-altitude regions. However, this study shows that CARTODEM is one of the finest DEM that can be used for the Indian subcontinent as it works more accurately over plain and moderately undulating lands.

Finite element solution to 3-D airborne time-domain electromagnetic problems in complex geological media using non-conforming hexahedral meshes

We propose the approach to 3-D modeling of the electromagnetic (EM) field in time-domain airborne EM problems in complex media including rugged topography and curved borders between the geological layers, target objects of different shapes, lateral inhomogeneity within subhorizontal layers. For discretization of the electromagnetic field in space, the vector finite element method is used. We propose the approach to generating the optimized non-conforming finite element meshes with hexahedral cells in which several finite elements can be attached to the face of the other finite element which allows achieving the significant reduction of computational costs in comparison with the regular meshes on which the numerical solution has the same accuracy. The optimized non-conforming finite element mesh in a complex medium with the topography and curved borders of layers is generated with the use of special transformations. The method of constructing the finite element approximations on these non-conforming hexahedral meshes is proposed. For discretization of the electromagnetic field in time, the implicit three-point scheme “with backward overstepping” is proposed. For solving the finite element SLAE, we use the direct solver PARDISO the effectiveness of which is achieved due to the use of time stepping with a piecewise constant step and grouping the calculations of the electromagnetic field in time steps and transmitter positions. In order to increase the accuracy of calculating the signal in the receiver, a special procedure of smoothing the magnetic field B in space and special scheme of approximating the derivative of B in time are proposed. The verification of the proposed approaches is performed using the solution for the 1-D model and solutions for 3-D models obtained by other authors. We present the results of the comparative analysis of different time schemes in finite element calculating the electromagnetic field and in calculating the signal (in the form of EMF) in the receiver and choose the optimal step and the number of subintervals with the constant steps into which the entire modeling time interval is divided. We perform the comparative analysis of stair-like approximation of curved surfaces with the use of rectangular parallelepipeds and approximation with the use of the hexahedral elements and choose the optimal parameters of generating the finite element meshes. We present the results of the analysis of the possibility of replacing the model with topography with the “flat” 3-D model in which the topography is taken into account by correcting the airborne system height. For the “flat” 3-D model, we present the results of the analysis of the computational effectiveness through the use of the primary-secondary field approach with automatic choice of a horizontally-layered medium for calculating the primary field. For the complex geolelectrical model with topography, laterally-inhomogeneous overburden with curved boundaries, target objects under overburden and for a great number of airborne system positions, the computational costs are presented for sequential and parallel modes for modeling time from 0.01 ms to 1 ms and 10 ms. We present the analysis of the topography effect, the influence of the inhomogeneities in the overburden and target objects in the complex media and show that in this conditions, to discover the target objects using the form of the signal is practically impossible, i.e. in order to discover the target objects in these complex media, it is required to perform a very fine 3-D interpretation for carrying out of which fast and high accuracy forward 3-D modeling is of great importance. We obtain that for calculating the field for one transmitter and the entire modeling time interval in the sequential mode on one core of PC with processor Intel i7-8700K CPU of 3.7 GHz and 32 GB of DRAM, the required computational time is about 4–6 s. The required computational time in the parallel mode with the use of six cores of this PC is about 0.65–1 s.

Topography Least-Squares Reverse-Time Migration Based on Adaptive Unstructured Mesh

Least-squares reverse-time migration (LSRTM) attempts to invert the broadband-wavenumber reflectivity image by minimizing the residual between observed and predicted seismograms via linearized inversion. However, rugged topography poses a challenge in front of LSRTM. To tackle this issue, we present an unstructured mesh-based solution to topography LSRTM. As to the forward/adjoint modeling operators in LSRTM, we take a so-called unstructured mesh-based “Grid Method.” Before solving the two-way wave equation with the Grid Method, we prepare for it a velocity-adaptive unstructured mesh using a Delaunay Triangulation plus Centroidal Voronoi Tessellation algorithm. The rugged topography acts as constraint boundaries during mesh generation. Then, by using the adjoint method, we put the observed seismograms to the receivers on the topography for backward propagation to produce the gradient through the cross-correlation imaging condition. We seek the inverted image using the conjugate gradient method during linearized inversion to linearly reduce the data misfit function. Through the 2D SEG Foothill synthetic dataset, we see that our method can handle the LSRTM from rugged topography.

Depth migration with the near surface: A case study for mineral exploration in China

Seismic reflection data used in mineral exploration are usually of poor quality because of rough topography and small-scale heterogeneities. However, there is an increasing demand for accurate imaging processes that can obtain such data. Here, we have developed a practical rugged depth migration method based on the finite-difference one-way wave equation. It can be used to improve imaging quality when faced with rough topography and complex geologic features. First, synthetic data are used to illustrate the errors and problems that cause unsatisfactory imaging results. This is usually because no consideration is given to rough topography during conventional processing procedures. To address this, a depth migration method that begins with the rugged topography is introduced. It can be used to produce better images. Real data from mineral exploration activities in Fujian, China, are then used to demonstrate the practical use of this method. We also compare two computational processes: The first corrects the data back to the original surface and then builds a velocity model before conducting rugged depth migration; the second process involves performing rugged depth migration on processed data featuring a smoothed surface following short-wavelength static correction and residual correction. The imaging results indicate that the section obtained from the processed data has better quality. They also indicate that the imaging quality of the original surface is affected by the built velocity model, which cannot include near-surface and small-scale structures.

Processing methodology for regional AEM surveys and local implications

ABSTRACTAirborne Electromagnetic (AEM) data are increasingly used in many geoscientific applications. BRGM conducted regional AEM surveys on the French overseas volcanic islands, where issues, including groundwater management or risk assessment are crucial. For such “infrastructural” surveys, the data are intended to be used for various purposes and over several years. In this type of environment, with a man-made imprint, a complex geology and rugged topography, the data processing can be very challenging. We therefore developed and implemented an original reprocessing method for regional AEM datasets. It aims to optimise, at a study scale, the coverage, the lateral and vertical resolution and the depth of investigation compared to more “standard” processing. This is highlighted through three examples. Our method includes regional processing procedures on both navigation and EM data: calculation of the effective tilt of the instrument frame, use of a DGPS-derived altitude, application of the singular value decomposition filtering and stacking with an adaptive trapezoid filter. Moreover, a local tuning of the inversion and manual editing are achieved for each study.

Improved landslide assessment using support vector machine with bagging, boosting, and stacking ensemble machine learning framework in a mountainous watershed, Japan

Heavy rainfall in mountainous terrain can trigger numerous landslides in hill slopes. These landslides can be deadly to the community living downslope with their fast pace, turning failures into catastrophic debris flows and avalanches. Active tectonics coupled with rugged topography in a complex geoenvironment multiplies this likelihood. The available hazard maps are usually helpful in mitigating disasters. However, fool-proof predicting landslide susceptibility identification remains a challenge in landslide discipline. Recently, ensemble machine learning (ML) techniques have proved the potential to provide a more accurate and efficient solution in spatial modeling. The main purposes of the current study are to examine and evaluate the predictive capability of support vector machine hybrid ensemble ML algorithms, i.e., the bagging, boosting, and stacking for modeling the catastrophic rainfall-induced landslide occurrences in the Northern parts of Kyushu Island, at the watershed scale in Japan. In this study, a landslide inventory map containing 265 landslide polygons was first interpreted from the aerial photographs and fieldwork after the September 2017 rainfall event. The raw data were randomly separated into two parts using a 70/30 sampling strategy for training and validating the landslide models. Then, 13 predisposing factors were prepared as predictors and dependent variable. The landslide susceptibility maps (LSM) were validated by the area under the receiver operating characteristic curve (AUC). The results of validation showed that the AUC values of the four models (SVM-Stacking, SVM, SVM-Bagging, and SVM-Boosting) varied from 0.74 to 0.91. The SVM-boosting model outperformed the other models, while SVM-stacking model has found to be the lowest performance. The outcome suggests that an ensemble ML model does not necessarily mean good performance. It is always preferable to select an appropriate model, such as the one proposed the hybrid novel ensemble SVM-boosting model, which could significantly improve the accuracies of LSM. Also, from Information Gain Ratio (IGR) we found that the rainfall factor mainly affects the results, that agrees with the analogy of present study.

The effect of small-scale morphology on thermal dynamics in coral microenvironments.

The thermal microenvironments of corals is a topic of current interest given their relationship to coral bleaching. We present computational fluid dynamics (CFD) model of corals with both smooth and rugged polyp surface topographies for two species of massive corals (Leptastrea purpurea and Platygyra sinensis) in order to predict their microscale surface warming. This study explores whether variation in polyp depth (PD) may directly effect a coral overall surface area-to-volume (A/V) ratio and consequently its surface warming. Validation of our models was made against detailed laboratory measurements of coral surface warming and thermal boundary layer thickness. Our results suggested that while differences in surface warming exist between smooth surfaces and surfaces covered in micro-polyps (5 mm depth), the variation in terms of surface warming is small (~0.18-0.19∘C) and it can be largely attributed to increasing A/V ratios. Our results demonstrated good agreement with measurements of surface temperatures on living corals and that ignoring the presence of polyps by modelling heat transfer associated with a smooth surface makes no material difference to the values obtained or the interpretation of the processes leading to surface warming.

Trend and Pattern of Cereal Crops: Production, Productivity and Area Coverage in Nepal

This study conducted to examine growth trends and pattern in area, production and productivity of major cereal crops over the six fiscal years. Time series data of cereal crops coverage of annual yield were used for the study. This study was based on descriptive nature and used secondary sources of information on production, productivity and area coverage of major cereals (Paddy, Maize, Wheat, Millet, Buckwheat and Barley) covering the six fiscal years (2011/12-20116/17) data. Trends of crop's productivity were analyzed using graphical methods. Ratio and percentage were used to measure productivity (yield) growth rate of the selected crops of study. The yielding trend of cereal production is not satisfactory in Nepalese economy. Pattern of agricultural production in Nepal is affected by multiple factors including rugged topography, monsoon, insignificant investment in infrastructure, and research and development. Production and productivity would be helpful to develop the future plans and take the appropriate decisions to uphold the situation for the sustainability in food production.

Evaluation of season long rainfall simulated by WRF over the NWH region: KF vs. MSKF

Abstract This study is aimed to assess the performance of Numerical Weather Predication (NWP) model Weather Research and Forecasting (WRF) in simulating the season long rainfall pattern over the North-West Himalayan (NWH) region. For this purpose, two experiments are designed with identical initial conditions but varying cumulus physics options viz.; Kain-Fritsch (KF) and Multi-scale Kain-Fritsch (MSKF). WRF simulations have been carried out for multiple nested domains (45, 15 and 5 km) configuration for monsoon season of 2017. Model derived rainfall corresponding to two experiments has been evaluated against the gridded rainfall data prepared by India Meteorological Department (IMD) and satellite based GPM-IMERGE and INSAT-3D HE-rain. Present results unveiled that the KF scheme overestimates the amount of rainfall over the entire study domain; whereas, MSKF scheme is capable to simulate the magnitude of rainfall comparable to the observations. Model simulated rainfall corresponding to both the experiments yields stronger correlation with satellite based GPM-IMERG as compared to the IMD data. It is noted based on statistically robust Chow test that the WRF simulation with KF scheme estimates break point in the rainfall pattern at 1200 m whereas WRF simulation with MSKF scheme resolves break point at 2000 m which is in close agreement with the previous studies. Categorical statistics metrics and qualitative analysis of WRF simulations suggest that the scale aware cumulus scheme MSKF performs better in resolving monsoon season rainfall pattern over the rugged topography of the NWH region. Present study has implications for improved understanding of spatial pattern of monsoon rainfall over the NWH region.

14C and 40Ar/39Ar radiometric dating and geologic setting of young lavas of Rancho Seco and Mazcuta volcanoes hosting archaeological sites at the margins of the Pátzcuaro and Zacapu lake basins (central Michoacán, Mexico)

Geologic mapping of two neighbouring areas (totalling ∼770km2) centred around the Rancho Seco and Mazcuta monogenetic scoria cones and situated between the Pátzcuaro and Zacapu lake basins in the Michoacán-Guanajuato Volcanic Field (central portion of the Trans-Mexican Volcanic Belt), allowed the recognition of 62 Quaternary monogenetic volcanic structures, which include cinder cones with associated lava flows, domes, and small-to-medium sized shields. 40Ar/39Ar and 14C radiometric dating, petrography, and whole-rock chemical analyses of volcanic products provide a stratigraphic framework and insight into different eruptive styles, and erupted volumes (∼45km3 of calc-alkaline magma). Pliocene to Holocene monogenetic activity has been frequent in this region, forming structures, which are generally aligned along an ENE-WSW direction associated to the Morelia-Cuitzeo-Acambay normal fault system.The young Rancho Seco and Mazcuta volcanoes are of particular interest because their distal lava flows host the pre-Hispanic archaeological urban centres of Angamuco and Cortijo Viejo, respectively. The Rancho Seco scoria cone was radiocarbon-dated at 27,845+445/−425yr BP and emitted at least six andesitic lava flows which were emplaced toward the SW (Lake Pátzcuaro) covering an area of 21.3km2 with a volume of ∼0.64km3. The Mazcuta scoria cone dated at 7970±135yr BP produced five basaltic andesite-andesite lava flows toward the NW (Lake Zacapu), where they cover an area of 28.85km2 with a volume of ∼0.57km3. The recently studied archaeological site of Angamuco became an important urban centre during the rise of the Tarascan Empire in the Post-Classic period (AD 900–1521), while the Cortijo Viejo site remains largely unexplored, but its occupation might fall within the same period. Although the young lava flows on which these sites are built seem inhospitable and barren with a rugged topography and rocky substrate unfit for agriculture, early inhabitants adapted and modified its surface according to their needs. Hence, these archaeological sites exemplify how a seemingly hostile landscape was ingeniously modified to establish population centres with patterns similar to those observed on lava flows elsewhere.

Characteristics, mechanisms and prevention modes of debris flows in an arid seismically active region along the Sichuan–Tibet railway route, China: a case study of the Basu–Ranwu section, southeastern Tibet

The Basu–Ranwu section of the Sichuan–Tibet railway is in an arid and tectonically active valley characterized by rugged topography, sharp river incision and severe debris flow events. The study aims to provide scientific support for the prevention and control of debris flow in this section by revealing the dynamic characteristics, main controlling factors and distribution rules of debris flow. Research based on the analysis of field investigation data, remote sensing images, DEM and geological map has yielded the following results: (1) the forty-eight debris flows in the study area can be divided into five types based on the formation conditions, which are zonally distributed along the fault zone and also varied vertically in space and depended on the hardness of the underlying strata. (2) A complex geological and environmental background has provided appropriate material sources and favourable potential energy conditions conducive to the formation of disastrous debris flows. Additionally, the development of debris flows was affected by antecedent earthquakes and droughts, and disastrous debris flows are triggered by an abundant source of water. (3) The study area is located in the arid area, where the rainfall runoff is small and the scale of debris flow is relatively small, except for a few glacial lake outburst debris flows; therefore, the debris flow in this section can be controlled; prevention modes of debris flow hazards have been proposed for the railway engineering based on the types of railway engineering and the scale and type of the debris flows. The results provide an important and object scientific basis for route selection for geological engineering projects and for the control of debris flows in the Basu–Ranwu section of the Sichuan–Tibet railway.

Revisiting Recent Elevation‐Dependent Warming on the Tibetan Plateau Using Satellite‐Based Data Sets

AbstractSatellite data, characterized by extensive regional coverage and relatively high spatial resolution, have a distinct advantage for examining elevation‐dependent warming (EDW) across rugged topography in mountain regions where there are sparse in situ observations. Based on recent (2001–2015) comprehensive satellite‐based data sets (2 m air temperature, land surface temperature, snow cover, and daytime and nighttime cloud), this study finds that annual mean 2 m air temperature warming rates show rapid decrease above 4,500 m despite increasing from 2,000 to 4,500 m. This indicates a reversal in EDW at the highest elevations on the Tibetan Plateau, which is somehow different from the EDW derived from short‐term land surface temperature presented in earlier research. The decrease of warming rate above 4,500 m coincides with the elevation at which most of the current solid water resources reside. Thus, their decline may be less rapid than previously thought. Trends in nighttime cloud and snow cover are both correlated with patterns of EDW on the Tibetan Plateau, but the leading factor varies on an annual and seasonal basis. These results provide important evidence for understanding EDW and its controlling mechanisms in an extreme high‐elevation context.

An aeromagnetic investigation of the Dapai deposit in Fujian Province, South China: Structural and mining implications

The Dapai region is considered as one of the largest polymetallic reserves in Fujian Province, South China. As exploration advances, so does the demand for prospecting the deeper concealed deposits in this place. However, in the past few years, due to the rugged surface topography and dense vegetation, few high-precision and large-scale ground surveys have been carried out in this area. Therefore, the understanding of the overall structure and non-exposed deposits remains insufficient to meet the challenges involved in deeper ore prospecting. In the present study, we applied a cost-effective and high-precision aeromagnetic survey to investigate the structural trends prevailing in the study area and delimit the areas with potential for finding deposits. To achieve the aforementioned goals, the tilt angle derivative was conducted on the pre-processed magnetic anomalies to highlight any deeply seated structural features, based on which reliability of the geologically-inferred faults was analyzed, and seven major faults and 22 minor faults were identified for the first time. Most of these deduced faults show an NS trend in the center part and an NW/NE trend in other parts of the study area. In addition, 3D generalized physical property inversion of the obtained residual magnetic anomalies was implemented to delineate the potential ore bodies, based on which an integrated prospecting target map was established. Our inversion results indicate that there are several isolated magnetic sources in the subsurface extending from a depth of a few hundred meters to no more than 3 km. This presented study not only leads to a deeper understanding of the Dapai deposit, but also provides references for studying other similar deposits where large-scale ground studies are hard to be executed.

High‐Resolution Snowline Delineation From Landsat Imagery to Infer Snow Cover Controls in a Himalayan Catchment

AbstractThe snow cover dynamics of High Mountain Asia are usually assessed at spatial resolutions of 250 m or greater, but this scale is too coarse to clearly represent the rugged topography common to the region. Higher‐resolution measurement of snow‐covered area often results in biased sampling due to cloud cover and deep shadows. We therefore develop a Normalized Difference Snow Index‐based workflow to delineate snow lines from Landsat Thematic Mapper/Enhanced Thematic Mapper+ imagery and apply it to the upper Langtang Valley in Nepal, processing 194 scenes spanning 1999 to 2013. For each scene, we determine the spatial distribution of snow line altitudes (SLAs) with respect to aspect and across six subcatchments. Our results show that the mean SLA exhibits distinct seasonal behavior based on aspect and subcatchment position. We find that SLA dynamics respond to spatial and seasonal trade‐offs in precipitation, temperature, and solar radiation, which act as primary controls. We identify two SLA spatial gradients, which we attribute to the effect of spatially variable precipitation. Our results also reveal that aspect‐related SLA differences vary seasonally and are influenced by solar radiation. In terms of seasonal dominant controls, we demonstrate that the snow line is controlled by snow precipitation in winter, melt in premonsoon, a combination of both in postmonsoon, and temperature in monsoon, explaining to a large extent the spatial and seasonal variability of the SLA in the upper Langtang Valley. We conclude that while SLA and snow‐covered area are complementary metrics, the SLA has a strong potential for understanding local‐scale snow cover dynamics and their controlling mechanisms.

Landslide susceptibility in Rasuwa District of central Nepal after the 2015 Gorkha Earthquake

The 2015 Gorkha Earthquake (7.8 Mw) triggered several landslides in central Nepal with major damages in 14 districts. Among them, the Rasuwa district at the north of Kathmandu Valley faced severe landslides due to rugged topography, complex geology and improper land use development. The landslides had blocked the Pasang Lhamu Highway and dammed the Trishuli River at many places. A total of 1416 landslide locations were detected in the district from high resolution satellite images in Google Earth. In this study, landslide susceptibility was modeled in the Rasuwa District by considering slope, aspect, elevation, geology, peak ground acceleration (PGA), land use, drainage proximity and thrust proximity as the predictive factors for landslide occurrences. The landslide inventory was split into 70% and 30% portions as the training dataset and testing dataset respectively. The results from modified frequency ratio (FR) suggest that effect of geology with prediction rate 2.52 is the highest among all factors and is followed by elevation (2.38) and drainage proximity (2.12). The results were verified using area under curve (AUC) and the prediction rate was found to be 79.14%. The computed landslide susceptibility map is helpful for land use planning and landslide risk reduction measure in the Rasuwa District.

The influence of fine‐scale topography on the impacts of Holocene fire in a Tasmanian montane landscape

ABSTRACTTasmania's montane temperate rainforests contain some of Australia's most ancient and endemic flora. Recent landscape‐scale fires have impacted a significant portion of these rainforest ecosystems. The complex and rugged topography of Tasmania results in a highly variable influence of fire across the landscape, rendering predictions of ecosystem response to fire difficult. We assess the role of topographic variation in buffering the influence of fire in these endemic rainforest communities. We developed a new 14 000‐year (14‐ka) palaeoecological dataset from Lake Perry, southern Tasmania, and compared it to neighbouring Lake Osborne (<250 m distant) to examine how topographic variations influence fire and vegetation dynamics through time. Repeated fire events during the Holocene cause a decline in montane rainforest taxa at both sites; however, in the absence of fire, rainforest taxa are able to recover. Montane temperate rainforest taxa persisted at Lake Perry until European settlement, whilst these taxa were driven locally extinct and replaced by Eucalyptus species at Lake Osborne after 2.5 ka. Contiguous topographic fire refugia within the Lake Perry catchment probably provided areas of favourable microclimates that discouraged fire spread and supported the recovery of these montane temperate rainforests. Copyright © 2019 John Wiley & Sons, Ltd.

Derivation of empirical relationships between geotechnical parameters and resistivity using electrical resistivity tomography (ERT) and borehole data at Sohag University site, upper Egypt

The new site is located in desert region of rugged topography. Quaternary boulders, gravels, sands and clays intercalation are the main rock types in the area. Geophysical evaluation of the subsurface lithology and structures using 2D and 3D electrical resistivity tomography (ERT) of the proposed site for construction was the main target of the present study, in addition finding empirical relationships between rock's electrical resistivity and some geotechnical parameters are also another target. Four geoelectrical resistivity layers were discriminated after the 2D inversion. Inspection of all 2D inverted profiles and 3D electrical resistivity depth slices showed rapid lateral and vertical variations in electrical resistivity values indicating heterogeneity in soil section. Clayey gravels or clayey sands and clays facies are predominant and hence swelling actions of the foundation beds is highly expected. The results of electrical resistivity tomography (ERT) were correlated with that inferred from the boreholes within the investigated area. The geotechnical parameters: liquid limit L.L%, plastic limit P.L%, free swelling F·S% and density Qu were calculated for representative samples collected from drilled boreholes. All samples showed considerably high L.L%, low to moderate P.L% with high F·S% which characterizes clayey soil. A trial for finding empirical relationships between the geotechnical properties and the rock electrical resistivity (L.L%, P.L%, F·S% and Qu) were carried out. These relations revealed that there is a considerable correlation between them when the rock has a resistivity more than 400 Ω m and poor correlation when the electrical resistivity is less than 400 Ω m. Accordingly, inferring applicable empirical equations between rock electrical resistivity and geotechnical parameters can be strong in the dry successions with a limited clays content, but in the wet or clayey soil materials the correlation will be weak and risky in application. From all obtained results and relationships, highly engineering awareness should be taken into account during establishing any construction in this site.

Comments on “A high resolution Mars surface gravity grid” (Górski et al., 2018, Planetary and Space Science 160, 84–106)

Górski et al. (2018, Planetary and Space Science 160, 84–106, https://doi.org/10.1016/j.pss.2018.03.015) developed a high-resolution surface gravity grid for Mars. They presented a comparison with the Mars Gravity Model 2011 (MGM2011) by Hirt et al. (2012, Planetary and Space Science 67, 147–154. https://doi.org/10.1016/j.pss.2012.02.006), which is based on similar input data, but a different computational methodology. These two models do not agree very well in their higher-frequency constituents, that is, the parts related to topography-induced gravity. In the spatial domain, the gravity accelerations from both models differ by ∼20 mGal (root-mean-square) and reach amplitudes as large as ∼695 mGal in places. Górski et al. (2018) suggest that some aspects of the MGM2011 modelling algorithm are “in error”, but without substantiating this claim nor verifying their model. In this communication, we present results from our validation experiments using alternative gravity modelling techniques, all showing a close fit with MGM2011, while being in clear disagreement (to a level of ∼40% of the signal) with the Górski et al. (2018) model. We discuss and narrow down the origin of the mismatches to a scale-factor of square-root (2), apparently included in their high-frequency modelling. As a general conclusion, our experiments indicate that the Górski et al. (2018) model should be treated with some caution, especially over rugged topography so long as the underlying modelling techniques are not comprehensively validated.

Debris flows with pore pressure and intergranular friction on rugged topography

The dynamic behavior of debris flows features the interplay of a non-hydrostatic pore-fluid pressure with the non-linear deformational behavior of the granular skeleton and the internal contact stress between grains. This complex physical background is considered by amending the classical depth-integrated modeling for granular-fluid flows by two additional fields, an extra pore-fluid pressure and a hypoplastic intergranular stress. A scaled and depth-integrated model is developed and transferred into a system of terrain-following coordinates, enabling the application on rugged topography. With this model, numerical investigations are carried out, using a non-oscillatory, shock-capturing central-upwind scheme. Parameter studies show the general impact of the additional fields, completed by comparison to the experimental results of a dam break scenario. Furthermore, application to the landslide event at the village of Hsiaolin in Taiwan, 2009, show the capability of the model to cope with large scale scenarios. The results show that the model and its implementation provide insights in the flow dynamics and the possibility to application on complex topography, considering an enhanced approach to the physics of debris flows.

High-precision local gravity survey along planned motorway tunnel in the Slovak Karst

Abstract Results from a detailed gravity survey realized along the planned highway tunnel in the karstic area of Slovak Karst in the eastern Slovakia are presented. Detailed gravity profiles crossed an area of rugged topography, therefore the terrain corrections played a crucial role in the gravity data processing. The airborne laser scanning technique (LiDAR) was used in order to compile a high-resolution digital terrain model (DTM) of the surrounding area and to calculate terrain corrections properly. The difference between the Bouguer anomalies calculated with an available nationwide DTM and those with new LiDAR-based model can be significant in some places as it is presented in the paper. A new method for Bouguer correction density analysis based on surface data is presented. Special underground gravity measurements in the existing nearby railway tunnel were also conducted in order to determine the mean density of the topographic rocks. The Bouguer anomalies were used to interpret lithological contacts and tectonic/karstic discontinuities.