Andrea Lugli

Landslide monitoring using multitemporal terrestrial laser scanning for ground displacement analysis

In the analysis of the temporal evolution of landslides and of related hydrogeological hazards, terrestrial laser scanning (TLS) seems to be a very suitable technique for morphological description and displacement analysis. In this note we present some procedures designed to solve specific issues related to monitoring. A particular attention has been devoted to data georeferencing, both during survey campaigns and while performing statistical data analysis. The proper interpolation algorithm for digital elevation model generation has been chosen taking into account the features of the landslide morphology and of the acquired datasets. For a detailed analysis of the different dynamics of the hillslope, we identified some areas with homogeneous behaviour applying in a geographic information system (GIS) environment a sort of rough segmentation to the grid obtained by differentiating two surfaces. This approach has allowed a clear identification of ground deformations, obtaining detailed quantitative information on surficial displacements. These procedures have been applied to a case study on a large landslide of about 10 hectares, located in Italy, which recently has severely damaged the national railway line. Landslide displacements have been monitored with TLS surveying for three years, from February 2010 to June 2012. Here we report the comparison results between the first and the last survey.

Effect of a balanced mixture of dietary fibers on gastric emptying, intestinal transit and body weight.

Background/Aims: Dietary fibers are frequently included in diets to decrease body weight, but their scarce palatability and the occurrence of meteorism prevent a long-term intake. The aim of this study was to test a mixture of dietary fibers expressly chosen to decrease their negative properties and strengthen their positive effects. Methods: In a series of 10 patients with a slight overweight, the effectiveness of a palatable dietary fibers mixture on gastric emptying and intestinal transit was tested with scintigraphic methods. Then, the effects on body weight and digestive sensations and characteristics of defecations, were evaluated for 4 weeks. Results: The intestinal transit was significantly shortened by the fiber intake, while the gastric emptying was delayed, but not significantly. The body mass index significantly and progressively decreased, whereas the sense of satiation significantly increased. No effect on abdominal bloating was referred, whereas a significant increase in number of defecations with stools of normal consistency was observed. The acceptability of the fiber mixture was good. Conclusions: The present research demonstrated that it is possible to prepare a palatable mixture of dietary fibers that maintains the property of decreasing body weight, favors the sense of satiation and accelerates the intestinal transit, with normalization of the stool consistency without the occurrence of meteorism.

Uncertainty in Terrestrial Laser Scanner Surveys of Landslides

Terrestrial laser scanning (TLS) is a relatively new, versatile, and efficient technology for landslide monitoring. The evaluation of uncertainty of the surveyed data is not trivial because the final accuracy of the point position is unknown. An a priori evaluation of the accuracy of the observed points can be made based on both the footprint size and of the resolution, as well as in terms of effective instantaneous field of view (EIFOV). Such evaluations are surely helpful for a good survey design, but the further operations, such as cloud co-registration, georeferencing and editing, digital elevation model (DEM) creation, and so on, cause uncertainty which is difficult to evaluate. An assessment of the quality of the survey can be made evaluating the goodness of fit between the georeferenced point cloud and the terrain model built using it. In this article, we have considered a typical survey of a landsliding slope. We have presented an a priori quantitative assessment and we eventually analyzed how good the comparison is of the computed point cloud to the actual ground points. We have used the method of cross-validation to eventually suggest the use of a robust parameter for estimating the reliability of the fitting procedure. This statistic can be considered for comparing methods and parameters used to interpolate the DEM. Using kriging allows one to account for the spatial distribution of the data (including the typical anisotropy of the survey of a slope) and to obtain a map of the uncertainties over the height of the grid nodes. This map can be used to compute the estimated error over the DEM-derived quantities, and also represents an “objective” definition of the area of the survey that can be trusted for further use.

Multi-temporal Terrestrial Laser Scanning Survey of a Landslide

Terrestrial laser scanning (TLS) has proven to be a very effective technique for landslides monitoring, even if some critical issues exist for providing highly reliable results. This chapter presents the methodology adopted in performing four surveys, carried out over three years on a large slump landslide in order to get effectively comparable data. The first problem concerns the setting up of the reference system, which has been realized by means of global navigation satellite system permanent stations ETRF00 datum. This solution was able to maximize the stability over time even at the expense of a slightly lower precision, which was, however, in the order of 1–2 cm with data recorded during the whole duration of TLS survey. An assessment of geo-referencing accuracy was carried out with respect to the only stable artifact present in the landslide area. This check pointed out that in the central part of the point cloud the repeatability between different surveys was slightly greater than 5 cm. To ensure the quality of the obtained multitemporal digital terrain models (DTM’s) over the entire region of interest, the choice of the interpolation algorithm has been performed and verified with a cross-validation method on the basis of a sample extracted from the data set. To detect the kinematics of the landslide in its several parts, both the DTM’s and profiles have been used, which have proven to be particularly useful for the interpretation of details. After the localization of various landslide bodies (keeping into account slope and aspect maps derived from the DTM), the evaluation of the volumes mobilized over time has been carried out by differencing the DTM’s. This analysis has been separately carried out in the different parts on which the landslide bodies had been subdivided.

Comparison of COSMO-SkyMed and RADARSAT-2 offset tracking results on David-Drygalski glacier (Antarctica) surface velocities

This note is about the comparison of coregistration offset tracking velocities of a glacier obtained with SAR sensors characterized by different wavelengths and spatial resolutions: Cosmo-SkyMED (X band) and RADARSAT-2 (C band). The study area is represented by the initial part of the David Glacier, in Antarctica, which is the most important outlet glacier of Victoria Land. Particular attention has been devoted to understand the role of polarization and penetration depth of the incident wavelength, which represent key parameters in determining the effective incidence angle and so, for this reason, affecting also derived velocities. Further investigation is needed to complete this analysis, considering also geophysical data and tidal effects. In particular, we focused our attention on the initial portion of the David glacier, comprising the grounding line (which is the line where the glacier begins to be floating on the sea surface), represented in fig. 3 [1]. The processed dataset consists of four COSMO-SkyMed (in the following simply CSK) Stripmap scenes and two RADARSAT-2 scenes in quad polarization Wide Fine Beam mode, made available respectively by Italian and Canadian Spatial Agencies through the “COSMO-SkyMed/RADARSAT-2 Initiative Joint Announcement of Opportunity” (Proposal id 2873/5247).

Why postprandial abdominal bloating in patients with irritable bowel syndrome does not respond to prokinetics.

Why Postprandial Abdominal Bloating in Patients With Irritable Bowel Syndrome Does Not Respond to Prokinetics

What is the origin of postprandial abdominal distension in patients with functional bloating and irritable bowel syndrome

TO THE EDITOR: In a relevant proportion of patients with functional bloating (FB) and irritable bowel syndrome (IBS) [1], abdominal distension starts or worsens after meals and during the day, until it reaches its peak in the evening and disappears during the night sleep. In some patients the abdominal distension is so rapid and intense such as to resemble a paralytic ileus. This phenomenon has been clearly demonstrated with inductance plethysmography [2] but, to date, nobody has offered a convincing explanation of the event. A number of hypotheses have been formulated [3], from an impairment of the abdominal viscerosomatic reflexes, which, however, does not explain why the abdominal wall in most cases is not flaccid, but tense and taut, to an increased presence of gas, which is a more probable occurrence [4,5]. With regard to the source of this gas, the early onset of distension after meals excludes colonic fermentation, while the hypotheses of aerophagia and endoluminal chemical reactions should also explain why the excess gas is not eructed or absorbed. We believe that the origin of this gas could be linked to a postprandial marked loss of tonic motor activity of the intestinal musculature, which increases the capacitance of the loops, favouring their filling by gas, with the following mechanism. When the intestinal tone is markedly decreased, the partial pressure of gas in the lumen is lowered, with two outcomes: the absorption of CO2 produced in great quantity after a meal is reduced and diffusion into the intestinal lumen of blood gases, such as nitrogen and oxygen, having a partial pressure higher than that of the intestinal lumen, takes place [6], giving rise to the abdominal distension. The excessive relaxation of the intestinal musculature, similar to that observed after glucagon administration [7], could be due to many factors, including the hyperfunction of inhibitory neuro-hormonal reflexes activated by endoluminal nutrients, especially lipids [8]. A role could also be played by overstimulation of the 5-HT7 receptors which participate in the accommodation process of the circular muscle together with nitric oxide (NO) released by descending inhibitory neurons during the preparation phase of intestinal peristalsis [9]. In addition, the intestinal wall distension stimulates tensoreceptors that activate inhibitory reflexes and the increased loop diameter requires a force of contraction to increase the endoluminal pressure higher than that of an intestine with a normal-sized lumen. Overcoming this vicious circle is a slow process and is usually only completely carried out during night sleep, presumably when the interdigestive clearing motility reappears, favouring both the reabsorption and the propulsion along the bowel of the gas pooled in the loops, as does the administration of prokinetics that restore the normal tonic motor activity of the intestine. In conclusion, we believe that the postprandial abdominal distension of patients with FB and IBS may be due to some sort of bowel paresis with increased loop capacitance, which both hinders the absorption of the intestinal gases and favours the diffusion of blood gases to the intestine, giving rise to the abdominal distension.

Use of DEMs Derived from TLS and HRSI Data for Landslide Feature Recognition

This paper addresses the problems arising from the use of data acquired with two different remote sensing techniques—high-resolution satellite imagery (HRSI) and terrestrial laser scanning (TLS)—for the extraction of digital elevation models (DEMs) used in the geomorphological analysis and recognition of landslides, taking into account the uncertainties associated with DEM production. In order to obtain a georeferenced and edited point cloud, the two data sets require quite different processes, which are more complex for satellite images than for TLS data. The differences between the two processes are highlighted. The point clouds are interpolated on a DEM with a 1 m grid size using kriging. Starting from these DEMs, a number of contour, slope, and aspect maps are extracted, together with their associated uncertainty maps. Comparative analysis of selected landslide features drawn from the two data sources allows recognition and classification of hierarchical and multiscale landslide components. Taking into account the uncertainty related to the map enables areas to be located for which one data source was able to give more reliable results than another. Our case study is located in Southern Italy, in an area known for active landslides.