Comparison of Remote Sensing Techniques for Geostructural Analysis and Cliff Monitoring in Coastal Areas of High Tourist Attraction: The Case Study of Polignano a Mare (Southern Italy)

Abstract

Rock slope failures in urban areas may represent a serious hazard for human life, as well as private and public property, even on the occasion of sporadic episodes. Prevention and mitigation measures indispensably require a proper rock mass characterization, which is often achieved by means of time-consuming, costly and dangerous field surveys. In the last decades, remote sensing devices such as high-resolution digital cameras, laser scanners and drones have been widely used as supplementary techniques for rock slope analysis and monitoring, especially in poorly accessible areas, or in sites of large extension. Although several methods for rock mass characterization by means of remote sensing techniques have been reported in specific studies, there are very few contributions that focused on comparing the different methods in an attempt to establish their advantages and limitations. With this study, we performed digital photogrammetry, Terrestrial Laser Scanning and Unmanned Aerial Vehicle surveys on a cliff located in a popular tourist attraction site, characterized by complex geological and geomorphological settings, as well as by disturbance elements such as vegetation and human activities. For each point cloud, we applied geostructural analysis by means of semi-automatic methods, and then compared multi-temporal acquisitions for cliff monitoring. By quantitative comparison of the results and validation by means of conventional geostructural field surveys, the pros and cons of each method were outlined in attempt to depict the conditions and goals the different techniques seem to be more suitable for.

The Use of Innovative Techniques for Management of High-Risk Coastal Areas, Mitigation of Earthquake-Triggered Landslide Risk and Responsible Coastal Development

“…Therefore, cliffs, steep slopes, hanging rocks, and morphological discontinuities in general, are either being scanned or photographed for the generation of a basement dataset on which further processing will be applied. The mapping of structural failures and rock discontinuity density at coastal cliffs proves to be very critical concerning the safety regime in the beaches beneath them, especially the popular ones [90].…”

Detection of geometric properties of discontinuities on the Špičunak rock slope (Croatia) using high-resolution 3D Point Cloud generated from Terrestrial Laser Scanning

“…Two methods stand out in the field of the engineering geological mapping of nearvertical rock slopes and tunnel excavation fronts: laser scanning (LS), digital photogrammetry (DP). Laser scanning methodology produces high-resolution and high-density 3D Point Clouds but with the limitation of much complex survey methodology and at a higher price [7,8]. Because of the accessibility of survey equipment, lower overall survey expense and much faster data acquisition for digital photogrammetry, it is used more often [9].…”

“…Because of the accessibility of survey equipment, lower overall survey expense and much faster data acquisition for digital photogrammetry, it is used more often [9]. It was concluded in [8] that both techniques have their advantages and disadvantages, and accessibility is the first factor to consider when choosing an appropriate Point Cloud acquisition method. If Terrestrial Laser Scanning (TLS) is accessible, it should be used to provide a more accurate and higher-density Point Cloud.…”

Evaluation of InfraRed Thermography Supported by UAV and Field Surveys for Rock Mass Characterization in Complex Settings

“…In this study, we present the results of a 24-h monitoring by means of infrared thermography on a rock cliff located in an urban, highly touristic, coastal site, characterized by vertical and lateral lithological heterogeneity, as well as by the presence of karst features. As a matter of fact, the mentioned factors proved to be disturbance elements during previous studies carried out on the same area by means of Terrestrial Laser Scanning (TLS) and UAV technologies for rock mass characterization and rockfall detection [39]. At the same time, the shrubs diffused throughout the rock mass, the artificial cavities and walls, as well as people moving in the field of view, perturbate the thermal outputs of the target in the form of thermal anomalies.…”