Value Of Slope Angle Research Articles

Soil erosion assessment using geomorphological remote sensing techniques: an example from southern Italy

AbstractThe aim of this study is to assess of the distribution and map the geomorphological effects of soil erosion at the basin scale identifying newly‐formed erosional landsurfaces (NeFELs), by means of an integration of Landsat ETM 7+ remotely sensed data and field‐surveyed geomorphological data. The study was performed on a 228·6 km2‐wide area, located in southern Italy. The study area was first characterized from a lithological, pedological, land‐use and morpho‐topographic point of view and thematic maps were created. Then, the georeferenced Landsat ETM 7+ satellite imagery was processed using the RSI ENVI 4.0 software. The processing consisted of contrast stretching, principal component analysis (PCA), decorrelation stretching and RGB false colour compositing. A field survey was conducted to characterize the features detected on the imagery. Particular attention was given to the NeFELs, which were located using a global positioning system (GPS). We then delimited the Regions of Interest (ROI) on the Landsat ETM 7+ imagery, i.e. polygons representing the ‘ground‐truth’, discriminating the NeFELs from the other features occurring in the imagery. A simple statistical analysis was conducted on the digital number (DN) values of the pixels enclosed in the ROI of the NeFELs, with the aim to determine the spectral response pattern of such landsurfaces. The NeFELs were then classified in the entire image using a maximum likelihood classification algorithm. The results of the classification process were checked in the field. Finally, a spatial analysis was performed by converting the detected landsurfaces into vectorial format and importing them into the ESRI ArcViewGIS 9.0 software. Application of these procedures, together with the results of the field survey, highlighted that some ‘objects’ in the classified imagery, even if displaying the same spectral response of NeFELs, were not landsurfaces subject to intense soil erosion, thus confirming the strategic importance of the field‐checking for the automatically produced data. During the production of the map of the NeFELs, which is the final result of the study, these ‘objects’ were eliminated by means of simple, geomorphologically‐coherent intersection procedures in a geographic information system (GIS) environment. The overall surface of the NeFELs had an area of 22·9 km2, which was 10% of the total. The spatial analysis showed that the highest frequency of the NeFELs occurred on both south‐facing and southwest‐facing slopes, cut on clayey‐marly deposits, on which fine‐textured and carbonate‐rich Inceptisols were present and displaying slope angle values ranging from 12° to 20°. The comparison of two satellite imageries of different periods highlighted that the NeFELs were most clearly evident immediately after summer tillage operations and not so evident before them, suggesting that these practices could have played an important role in inducing the erosional processes. Copyright © 2009 John Wiley & Sons, Ltd.

Experimental simulation of martian gully forms

Gullies are widespread on slopes on the surface of Mars and have been investigated by numerous authors, yet their formation processes remain elusive. In an attempt to understand the possibility of a water-based origin for these forms, we undertook a series of flume experiments at Earth surface temperatures and pressures. Our objectives were to produce forms that resemble those most commonly observed on Mars, documenting their morphometric characteristics and identifying any statistically significant relationships between form and controlling factors of slope and flow rate. Experiments were conducted in a 1×1.5 m 2 flume filled with medium grain size sand. The experiments were run over a slope angle range of 10–30°, corresponding to the range for gullies on Mars. Water from a constant-head tank fed through 5 mm silicone hose to a rotameter and then released just below the surface at the top of the slope. Gullies were produced at slope angle values of 10°, 20°, and 30° and flow rate values of 445, 705, 965, and 1260 mL min −1 at each angle. Eighteen parameters were identified and subsequently measured on each gully produced in the flume. Gully forms were successfully reproduced and displayed development of the fundamental morphological components observed on Mars: alcove, channel, and apron. Slope–gully form relationships for each component revealed the following results: higher slope angles formed shorter gullies with thicker apron deposits. Moreover, longer gullies were seen at higher flow rates. We concluded that forms visually similar to those observed on Mars can be created by water in the laboratory flume under terrestrial conditions. Morphometric parameters can be measured and permit identification of controlling factors. Experimental simulation of gullies appears possible with proper scaling of experimental parameters. Although not directly scalable to Mars, flume gully parameters may be used to develop numerical models in the future.

GUIDANCE AND ATTITUDE CONTROL LAW FOR THE FINAL PART OF A REENTRY VEHICLE TRAJECTORY - ALTERNATE LAWS FOR THE EXPERIMENTAL VEHICLE HSFD II

The experimentation part of HSFD-II (High Speed Flight Demonstrator phase II) was conducted under a CNES (French Space Agency) - JAXA (Japaneese Space Agency) cooperation. JAXA provided the instrumented mock-up and CNES provided stratospheric ascending balloons (for mock-up release at up to 30 km in altitude) at the Kiruna-Esrange (Sweden) test falicity. In the terms of the cooperation was included the development of an alternate set of guidance and attitude control laws provided by ONERA.The control law was obtained using a robust polytopic method. The original guidance law of the US Shuttle was used as a baseline, but with significant adaptations, in particular for deep slope angle values (down to -50° in guidance phase versus about -5° for the Shuttle).The article first recalls the Flight Mechanics equations involved along with notations. The principle of the attitude control law is indicated and the guidance law is detailed. Finally the results of worst case simulations are presented.

Effects of Digital Elevation Model Errors on Spatially Distributed Seismic Slope Stability Calculations: An Example from Seattle, Washington

More than 1,600 centimeter-accurate differential GPS measurements show that elevation errors in a 10-m digital elevation model (DEM) covering an 18-km 2 portion of Seattle can have significant effects on calculated values of slope angle, static factor of safety, Newmark acceleration, and slope displacement. Declustered error data from the study area have a mean of ! 0.92 m and a standard deviation of 62.36 m, comparable to results reported by others. Conditional Gaussian simulation and normal score back-transformation were used to create 25 error realizations with the same statistical distribution and spatial correlation as the measured errors, and the error realizations were subsequently used to create elevation, slope angle, static factor of safety, Newmark acceleration, and displacement realizations. The maximum slope angle uncertainty magnitude decreases frommorethan108toabout48asslopeangleincreases, but the minimum slope angle uncertainty varies between 618 and 628 regardless of slope angle. Typical slope angle standard deviations arising from DEM errors are in the range of 638 to 648. The resulting uncertainties in calculated Newmark displacements as the consequence of a hypothetical large earthquake affecting the study area (Arias intensity of 4 m/s) are in most cases less than 63 cm, but some values are greater than 610 cm. If the acceptable maximum probability of misclassifying a potentially unstable area as stable is decreased from 50 to 5 percent, incorporation of displacement uncertainty into the calculusofhazardincreasesfrom0.6to4.1percentthe portion of the study area that may be susceptible to landsliding as a result of the hypothetical earthquake.

The application of three-dimensional DDA with a spherical rigid block to rockfall simulation

Rockfalls pose a substantial threat to ground transportation, due to their rapidity, destructive potential and high probability of occurrence on steep topographies, often found along roads and railway routes. Approaches for the assessment of rockfall susceptibility range from purely phenomenological methods and statistical methods, suitable for modeling large areas, to purely deterministic ones, usually easier to use in local analyses. A common requirement is the need to locate potential detachment points, often found uphill on cliffs, and the subsequent assessment of the runout areas of rockfalls stemming from such points.Here, we apply a physically based model for the calculation of rockfall trajectories along the whole Italian railway network, within a corridor of total length of about 17,000 km and varying width. We propose a data-driven method for the location of rockfall source points based on expert mapping of potential source areas on sample representative locations. Using empirical distributions of gridded slope angle values in source areas mapped by experts, we derived probabilistic maps of rockfall sources in the proximity of the railway network, regardless of a particular trigger.Source areas act as starting points of simulated trajectories within the three-dimensional model STONE. The program provides a pixel-by-pixel trajectory count, covering 24,500 km2 and representing the largest homogeneous application of the model to date. We classified the raster map into a vector susceptibility map, analyzing the railway track as a collection of segments, for which we provide segment-wise rockfall susceptibility.Eventually, we considered an equivalent graph representation of the network, which helps classifying the segments both on the basis of rockfall susceptibility and the role of each segment in the network, resulting in a network-ranked susceptibility. Both maps are useful for subsequent hazard assessment, and to prioritize safety improvements along the railway, at national scale.

Le rôle du cône apical dans le déclenchement des coulées de débris alpines du massif du Dévoluy, Hautes-Alpes (France)

Si de nombreuses recherches ont porté sur les conditions de déclenchement des coulées de débris alpines, en particulier les précipitations de forte intensité, et sur les modalités de leur écoulement, plus rares ont été les travaux portant sur les conditions d'approvisionnement en matériaux. Le but de ce travail est de présenter les résultats d'observations et de mesures portant sur une population de 68 modelés de coulées de débris, étudiés autour du plateau de Bure, situé à 2600m d'altitude, un secteur du massif du Dévoluy dans les Alpes françaises. On recense chronologiquement tous les modelés (entre 1948 et 1997), on les cartographie et on recherche dans les archives météorologiques les circonstances météorologiques de chaque cas de coulée. Les résultats correspondent à ceux des autres auteurs, mais les relations entre les données météorologiques et le déclenchement des coulées ne sont pas statistiquement significatives. Des observations complémentaires, portant sur les caractères morphosédimentaires de la zone d'alimentation et de la zone amont des modelés de coulées de débris, permettent de mettre en évidence une topographie originale appelée cône apical, situé à la limite entre la paroi et le dépôt de pente, secteur où s'accumule le matériel sédimentaire qui est mobilisé par la coulée de débris. Sans cette accumulation préalable et même si les conditions météorologiques sont favorables, la coulée de débris ne peut se produire. Inversement, certaines coulées peuvent se déclencher même si les conditions météorologiques ne sont pas exceptionnelles lorsque le stock sédimentaire est abondant. Le déclenchement est en grande partie commandé par les rythmes d'accrétion.

The contribution of radiant heat transfer to laboratory-scale fire spread under the influences of wind and slope

Abstract In a previous study, a two-dimensional non-stationary model of fire spread across a fuel bed including slope effects was proposed. Enhancement of the radiant heat transfer process ahead of the fire front under wind and slope conditions is provided in the current paper. Predictions are compared to data recorded during laboratory-scale experimental fires conducted across different pine needles bed under wind and slope conditions. Influence of these environmental factors on rate of spread, temperature–time profiles and fire front shapes is then presented. Predictions reveal that effects of flame radiation alone can account for observations up to limit value of slope angle and wind velocity for which convective mechanisms cannot be neglected. Below this limit observations are quantitatively well reproduced by the model.

Landform analysis of slope movements using DEM in Higashikubiki area, Japan

Various numerical analyses using 25 m-grid DEMs were compared with rasterized slope movement distribution maps and geological maps of the Higashikubiki area in Niigata Prefecture, Japan. Slope movement distribution maps included five classes: “stable slope”, “landslide mass”, “landslide scarp”, “collapse scarp” and “crack”. Their statistical characteristics were clarified by numerical landform analyses for each lithology. Frequency distributions of slope angle were nearer to a normalized distribution for landslide masses than for stable slopes. From the difference of mean slope degrees of landslide masses and that of stable slopes, it was estimated that the smallest slope angle at which landslides occur is approximately 10° for sandy formations. Moreover, mean values of slope angle in the total study area and total landslide masses were both approximately 14°. For sedimentary rocks, graphs of mean slope for each elevation zone of landslide mass and stable slope were parallel, and slope angle did not increase above approximately 100–160 m. For landslide masses and collapse scarps, the relationship between slope and convexity or roughness showed a regular relation closely resembling linear or quadratic function.

Landslide susceptibility mapping of the slopes in the residual soils of the Mengen region (Turkey) by deterministic stability analyses and image processing techniques

The aim of the present study is to prepare a landslide susceptibility map of a region of about 120 km 2, between Gökcesu and Pazarköy (around Mengen, NW Turkey) at approximately 10 km north of the North Anatolian Fault Zone, where frequent landslides occur. For this purpose, mechanisms of the landslides were studied by two-dimensional stability analyses together with field observations, and the parameters controlling the development of such slides were identified. Field observations indicated that the failures generally developed within the unconsolidated and/or semiconsolidated soil units in forms of rotational, successive shallow landslides within the weathered zone in Mengen, Cukurca and Sazlar formations. Although consisting of residual soils, Capak and Gökdag formations do not exhibit landslides as the natural slopes formed on these, do not exceed the critical slope angles. Statistical evaluations and distribution of the landslides on the topographical map showed that such parameters as cohesion, angle of internal friction, slope, relative height, orientation of slopes, proximity to drainage pattern, vegetation cover and proximity to major faults were the common features on the landslides. Digital images were obtained to represent all these parameters on gray scale on the SPOT image and on the digital elevation model (DEM) of the area using image processing techniques. Soil mechanics tests were carried out on 36 representative samples collected from different units, and parameters were determined for two-dimensional stability analyses basing on “sensitivity approach” and for the preparation of digital shear strength map. In order to determine the critical slope angle values for the residual soils, a series of sensitivity analyses were realized by using two-dimensional deterministic slope stability analyses techniques for varying values of cohesion, angle of internal friction and slope height along with varying saturation conditions. According to the results of the sensitivity analyses, the Mengen formation was found to be most susceptible unit to landslides, covering about 33.5% of the region studied in terms of surface area. The distribution of the critical slopes were determined by superimposing the critical slope values from sensitivity analyses on slope map of the study area. On the other hand, iso-cohesion and iso-friction maps were produced by locating the values of cohesion and internal friction angles in a geographic coordinate system such that they coincide with sample locations on the DEM and by further interpolation of the values concerned. The pixel values were evaluated in gray scale from 0 to 255, 0 representing the lowest pixel value and 255 representing the highest. Sensitivity analyses on cohesion and angle of internal friction to investigate the effects of these parameters only on stability, revealed that cohesion was effective at a rate of 70% by itself, while angle of internal friction alone controlled the stability by a rate of 30%. The iso-cohesion and iso-friction maps previously obtained were digitally combined in these rates and a “shear strength map” was prepared. The geographic setting of the study area is such that northern slopes usually receive dense precipitation. In relation to this fact, about 42% of the landslides are due north. Thus, a slope orientation map was prepared using the DEM, and slopes facing north were evaluated as being more susceptible to sliding. Proximity to the drainage pattern was another important factor in the evaluation, as streams could adversely affect the stability by either eroding the toe or saturating the slope, or both. When considered together, in conjunction with the field observations, faults and landslides showed a close association. In the area, about 88% of the landslides were detected within an area closer than 250 m to major faults, therefore, a main discontinuity map was produced using the SPOT image of the region, and “proximity to major faults” was evaluated as a parameter as most of the landslides developed in areas where the vegetation was rather sparse. A vegetation cover map was therefore obtained from the SPOT image, and the areas with denser vegetation were considered to be less susceptible to sliding with respect to the areas with less or no vegetation. Having prepared the maps accounting for the distribution of critical slopes, shear strength properties, relative height, slope angle, orientation of the slopes, vegetation cover, proximity to the drainage pattern, geographic corrections were carried on each of these, and a potential failure map was obtained for the residual soils by superimposing all these maps. Next, a classification was performed on the final map and five relative zones of susceptibility were defined. When compared with this map, all of the landslides identified in the field were found to be located in the most susceptible zone. The performance of the method used in processing the images appears to be quite high, the zones determined on the map being the zones of relative susceptibility.

MACHINE-PRINTED CHINESE CHARACTER RECOGNITION BASED ON LINEAR REGRESSION

Segmented machine-printed Chinese characters generally suffer from small distortions and small rotations due to noise and segmentation errors. These phenomena cause many conventional methods, especially those based on directional codes, to be unable to reach very high recognition rates, say above 99%. In this paper, regressional analysis is proposed as a means to overcome these problems. Firstly, thinning is applied to each segmented character, which is enclosed in a proper square box and also filtered for noise reduction beforehand. Secondly, the square thinned character image is divided into 9×9 meshes (blocks), instead of the conventional 8×8, for reasons of the Chinese character's characteristics and also for global feature extraction. Thirdly, line regression is applied, for all black points in each block, to obtain either the value of the slope angle, or a dispersion code which is derived from the sample correlation coefficient after proper transformation. Thus, each block is coded by one of three cases: 'blank', value of slope angle, or 'dispersion'. The peripheral blacks are used for preclassification. Proper scores for matching two characters are designed so that learning and recognition are quite efficient. The objective of designing this optical character recognition system is to get very small misrecognition rates and tolerable rejection rates. Experiments with three fonts, each consisting of 5401 characters, were carried out. The overall rejection rate is 1.25% and the overall misrecognition rate is 0.33%. These are acceptable for most users.

Experimental investigation of combined forced and free convection in horizontal and inclined tubes

This investigation considers the effects of free convection on the laminar flow of water through a circular duct having essentially constant wall heat transfer rate per unit length of the duct and circumferentially uniform wall temperature. The effect of the Reynolds and Rayleigh number variations on heat transfer results has been analysed for both horizontal and inclined pipe. The experiment has covered the range of the inlet Reynolds number from 200 to 2300, and of the Rayleigh number from 6,000 to 70,000. The effect of pipe inclination has been investigated for slope angle values up to 60°, with laminar ascending flow.

Kinematic subsurface stormflow

This paper builds on the analysis of Henderson and Wooding (1964) in comparing simplified models of subsurface stormflow for the case of a sloping soil mantle in which the hydraulic conductivity is constant throughout. It is shown that models based on a kinematic wave formulation may be good approximations for those based on the extended Dupuit‐Forchheimier assumptions for values of the nondimensional parameter λ = 4i cos θ/(K sin2θ) less than about 0.75 in terms of predicting both water table profiles and subsurface stormflow hydrographs. By using this critical value of λ the range of values of slope angle and saturated hydraulic conductivity for which the kinematic approximation is valid can be specified. A comparison is made with slope angles and hydraulic conductivities at field sites where subsurface stormflow has been shown to be an important component of catchment storm response. It is concluded that the kinematic approximation may be useful for cases of practical interest.