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Physical Principles Of Remote Sensing

During the last decade, terrestrial laser scanning
(TLS) has appeared as a new surveying technique. Its
proper use requires good knowledge of the error
sources, comprehensive description of which is
currently lacking. Especially important are
systematic instrumental errors, which are determined
during calibration. Recently, the method of self-
calibration used in photogrammetry has been shown to
be efficient for laser scanners. Another important
task in TLS is georeferencing – transformation of
the point clouds into a specific coordinate system.
This book provides a systematic description of the
error sources in TLS surveys conducted with direct
georeferencing. Further, a new, unified approach for
laser scanner self-calibration is described, and the
results of calibration of three scanners are
reported. Finally, a prototype combined TLS survey
system is presented, which employs GPS for direct
georeferencing of the point clouds, and can be used
for accurate surveys of built environments. The book
should be useful to students and researchers in
Engineering Surveying as well as surveyors in public
and private sector.

Terrestrial laser scanning

Highways and railroads situated within rugged terrain are often subjected to the hazard of rockfalls. The task of assessing roadside rockmasses for potential hazards typically involves an on-site visual investigation of the rockmass by an engineer or geologist. At that time, numerous parameters associated with discontinuity orientations and spacing, block size (volume) and shape distributions, slope geometry, and ditch profile are either measured or estimated. Measurements are typically tallied according to a formal hazard rating system, and a hazard level is determined for the site. This methodology often involves direct exposure of the evaluating engineer to the hazard and can also create a potentially non-unique record of the assessed slope based on the skill, knowledge and background of the evaluating engineer. Light Detection and Ranging (LiDAR)–based technologies have the capability to produce spatially accurate, high-resolution digital models of physical objects, known as point clouds. Mobile terrestrial LiDAR equipment can collect, at traffic speed, roadside data along highways and rail lines, scanning continual distances of hundreds of kilometres per day. Through the use of mobile terrestrial LiDAR, in conjunction with airborne and static systems for problem areas, rockfall hazard analysis workflows can be modified and optimized to produce minimally biased, repeatable results. Traditional rockfall hazard analysis inputs include two distinct, but related sets of variables related to geological or geometric control. Geologically controlled inputs to hazard rating systems include kinematic stability (joint identification/orientation) and rock block shape and size distributions. Geometrically controlled inputs include outcrop shape and size, road, ditch and outcrop profile, road curvature and vehicle line of sight. Inputs from both categories can be extracted or calculated from LiDAR data, although there are some limitations and special sampling and processing considerations related to structural character of the rockmass, as detailed in this paper.

Evaluating Roadside Rockmasses For Rockfall Hazards From Lidar Data:Optimizing Data Collection And Processing Protocols

Infrared thermography is a growing technology in the engineering geological field both for the remote survey of rock masses and as a laboratory tool for the non-destructive characterization of intact rock. In this latter case, its utility can be found either from a qualitative point of view, highlighting thermal contrasts on the rock surface, or from a quantitative point of view, involving the study of the surface temperature variations. Since the surface temperature of an object is proportional to its emissivity, the knowledge of this last value is crucial for the correct calibration of the instrument and for the achievement of reliable thermal outcomes. Although rock emissivity can be measured according to specific procedures, there is not always the time or possibility to carry out such measurements. Therefore, referring to reliable literature values is useful. In this frame, this paper aims at providing reference emissivity values belonging to 15 rock types among sedimentary, igneous and metamorphic categories, which underwent laboratory emissivity estimation by employing a high-sensitivity thermal camera. The results show that rocks can be defined as “emitters”, with emissivity generally ranging from 0.89 to 0.99. Such variability arises from both their intrinsic properties, such as the presence of pores and the different thermal behavior of minerals, and the surface conditions, such as polishing treatments for ornamental stones. The resulting emissivity values are reported and commented on herein for each different studied lithology, thus providing not only a reference dataset for practical use, but also laying the foundation for further scientific studies, also aimed at widening the rock aspects to investigate through IRT.

Rock Emissivity Measurement for Infrared Thermography Engineering Geological Applications

Hazard and risk assessment procedures of different types of rockfall were analyzed to compare their outcomes when they are applied to the same case study. Although numerous methodologies are available in literature, rockfall hazard and risk analyses are often limited to standard estimations, affected by a margin of uncertainty, especially when relevant engineering projects are about to be realized. Based on the design purpose, different types of approaches can be chosen among the qualitative and quantitative ones available in literature, which allow different levels of analysis. One of the main criticisms related to rockfall events is the risk affecting linear structures, such as road or railways, due both to their strategic relevance for trade and communications and to the great entity of the exposed value (traffic units) traveling along them. In this perspective, a comparison between the qualitative method known as Evolving Rockfall Hazard Assessment (EHRA), the semi-quantitative modified Rockfall Hazard Rating System (RHRS) and the quantitative Rockfall Risk Management (RoMa) approach is herein commented according to a practical application to a case study. It is the case of the rockfall threat along slopes crossed by a strategic road connecting two of the most known spots of eastern Sicily (Italy), at the Taormina tourist complex. Data were retrieved from both recent literature and technical surveys on field. Achieved results highlight how the approaches are affected by a different level of detail and uncertainty, arising also by some necessary assumption that must be taken into account, especially when mitigation measures or territory planning have to be designed. Achieved results can be also taken into account for similar studies worldwide, in order to choose the most suitable procedure based on the design purpose. This is indeed crucial in the perspective of the optimization of time and economic resources in the territorial planning practice.

Comparing rockfall hazard and risk assessment procedures along roads for different planning purposes

The research presented in this paper is aimed at testing an innovative surveying protocol based the integration of quick methodologies employed for the characterization of a carbonate cliff affected by a rockfall and showing signs of further instability. During a post-rockfall emergency, one of the most important activities is evaluating if reactivation of the movements is possible, and if it may represent a threat for a series of elements at risk. On 5 January 2019, intense rainfalls triggered the detachment of a significant volume of fractured limestone and dolostone below the main square of a historical village located in southern Italy in the municipality of Messina, giving rise to one of the greatest landslides occurred at one of the most tourist areas of northeastern Sicily. Fallen blocks damaged the two main infrastructures of the area reaching also a bus terminal, which fortunately was vacant at the time of the rockfall. With the aim of proposing a quick surveying protocol during a post-rockfall emergency, terrestrial laser scanner, infrared thermography, and horizontal to vertical spectral ratio surveys were employed for the geostructural characterization of the cliff and for the investigation of the subsoil below the main square. In particular, the survey through terrestrial laser scanner returned an accurate 3D model of the cliff, where some key structures were highlighted; infrared thermography allowed recognizing caves and fractures along the cliff, with specific reference to a hollow area arising from past rockfalls. Such remote data, along with direct rock mass surveys performed by expert climbers allowed ascertaining that the instability of this cliff is driven by wedges formed by the intersection of 2 and 3 discontinuity systems, which are likely related to the main tectonic systems of the area. The horizontal to vertical spectral ratio survey allowed the identification of a peculiar vertical contrast of impedance, which may be related to a mechanical discontinuity located below the main square of the village, well matching with one of the systems responsible of the instability. The integration of these surveys methodologies resulted a useful quick protocol for the achievement of the key information on the stability of a rock cliff in the initial stage of its securing.

D. Salerno

Papers

A quick combined approach for the characterization of a cliff during a post-rockfall emergency