Technical Challenges for Multi-Temporal and Multi-Sensor Image Processing Surveyed by UAV for Mapping and Monitoring in Precision Agriculture

Precision Agriculture (PA) is an approach to maximizing crop productivity in a sustainable manner. PA requires up-to-date, accurate and georeferenced information on crops, which can be collected from different sensors from ground, aerial or satellite platforms. The use of optical and thermal sensors from Unmanned Aerial Vehicle (UAV) platform is an emerging solution for mapping and monitoring in PA, yet many technological challenges are still open. This technical note discusses the choice of UAV type and its scientific payload for surveying a sample area of 5 hectares, as well as the procedures for replicating the study on a larger scale. This case study is an ideal opportunity to test the best practices to combine the requirements of PA surveys with the limitations imposed by local UAV regulations. In the field area, to follow crop development at various stages, nine flights over a period of four months were planned and executed. The usage of ground control points for optimal georeferencing and accurate alignment of maps created by multi-temporal processing is analyzed. Output maps are produced in both visible and thermal bands, after appropriate strip alignment, mosaicking, sensor calibration, and processing with Structure from Motion techniques. The discussion of strategies, checklists, workflow, and processing is backed by data from more than 5000 optical and radiometric thermal images taken during five hours of flight time in nine flights throughout the crop season. The geomatics challenges of a georeferenced survey for PA using UAVs are the key focus of this technical note. Accurate maps derived from these multi-temporal and multi-sensor surveys feed Geographic Information Systems (GIS) and Decision Support Systems (DSS) to benefit PA in a multidisciplinary approach

Geodetic measurements to control a large research infrastructure: the Virgo detector at the European Gravitational Observatory

The Advanced Virgo (AdV) detector is a 3 km long arms Michelson interferometer for gravitational waves detection. The management of a complex and large research infrastructure requires high-precision geodetic surveying for positioning and rearrangement of instruments. This paper describes the establishment of Virgo Reference System (VRS) consisting in a wide-scale high precision geodetic network based on GPS and Total Station measurements, that support the positioning and the alignment of the different elements forming the interferometer. Ground settlement monitoring is strictly required to verify and adapt the interferometer vertical alignment in presence of a steady subsidence process due to infrastructures overloads. The paper describes also the monitoring activity conducted over the years by means of periodic high precision levelling, that was compared with the results with those obtained using differential interferometry based on satellite Synthetic Aperture Radar (SAR) data

3D DIGITISATION IN CULTURAL HERITAGE KNOWLEDGE AND PRESERVATION: THE CASE OF THE NEPTUNE STATUE IN BOLOGNA AND ITS ARCHETYPE

Abstract. In the field of Cultural Heritage, the availability of a complete, detailed and photo-realistic 3D model of the objects of interest permits to describe all the aspects related to geometry, colours and materials, as well as the work techniques and the decay state. Besides, it offers multiple possibilities for the documentation, the analysis and the study.This paper describes the experience, carried out by the DICAM Geomatics group of the University of Bologna, about the 3D digitisation of two important statues of Neptune, by means of the integration of 3D image-based and range-based techniques. The two artworks, both realized by the sculptor Giambologna, are the big bronze statue of the god adorning the homonymous fountain, one of the most symbolic monuments of the city of Bologna, and its archetype, exhibited in one of the civic museums.The obtained 3D models, beyond the important function of documentation, knowledge and preservation of the two objects, also permit a comparison between the small archetype, conveniently scaled, and the big final statue. In the manuscript all the surveying and data processing operations concerning the objects digitisation are described. Particular attention is paid to the problems related to the scale of the archetype and the comparison between the two obtained 3D models, with the aim to evaluate and represent the occurred changes

3D GEOMATICS TECHNIQUES FOR AN INTEGRATED APPROACH TO CULTURALHERITAGE KNOWLEDGE: THE CASE OF SAN MICHELE IN ACERBOLI'S CHURCHIN SANTARCANGELO DI ROMAGNA

The modern Geomatics techniques, such as Terrestrial Laser Scanner (TLS) and multi-view Structure from Motion (SfM), are gaining more and more interest in the Cultural Heritage field. All the data acquired with these technologies could be stored and managed together with other information in a Historical Building Information Model (HBIM). In this paper, it will be shown the case study of the San Michele in Acerboli's church, located in Santarcangelo di Romagna, Italy. This church, dated about the 6th century A.D., represents a high relevant Romanic building of the high Medieval period. The building presents an irregular square plan with a different length of the lateral brick walls and a consequential oblique one in correspondence of the apse. Nevertheless, the different lengths of the lateral brick walls are balanced thanks to the irregular spaces between the windows. Different changes occurred during the centuries, such as the closing of the seven main doors and the building of the bell tower, in the 11th century A.D., which is nowadays the main entrance of the church. An integrated survey was realized, covering the exterior and the interior. The final 3D model represents a valid support not only for documentation, but also to maintain and manage in an integrate approach the available knowledge of this Cultural Heritage site, developing a HBIM system in which all the mentioned historical, geometrical, material matters are collected

Integration of geomatics techniques for digitizing highly relevant geological and cultural heritage sites: The case of san Leo (Italy)

The research activities described in this contribution were carried out at San Leo (Italy). The town is located on the top of a quadrangular rock slab affected by a complex system of fractures and has a wealth of cultural heritage, as evidenced by the UNESCO's nomination. The management of this fragile set requires a comprehensive system of geometrical information to analyse and preserve all the geological and cultural features. In this perspective, the latest Geomatics techniques were used to perform some detailed surveys and to manage the great amount of acquired geometrical knowledge of both natural (the cliff) and historical heritage. All the data were also georeferenced in a unique reference system. In particular, high accurate terrestrial laser scanner surveys were performed for the whole cliff, in order to obtain a dense point cloud useful for a large number of geological studies, among others the analyses of the last rockslide by comparing pre-And post-event data. Moreover, the geometrical representation of the historical centre was performed using different approaches, in order to generate an accurate DTM and DSM of the site. For these purposes, a large scale numerical map was used, integrating the data with GNSS and laser surveys of the area. Finally, many surveys were performed with different approaches on some of the most relevant monuments of the town. In fact, these surveys were performed by terrestrial laser scanner, light structured scanner and photogrammetry, the last mainly applied with the Structure from Motion approach. \ua9 Authors 2017. CC BY 4.0 License

Terrestrial Remote Sensing techniques to complement conventional geomechanical surveys for the assessment of landslide hazard: The San Leo case study (Italy)

The San Leo village, located near to Rimini (northern Italy), was built in the medieval period on the top of a calcarenite and sandstone plateau, affected by lateral spreading associated with secondary rock falls and topples. In fact, a number of landslides endangered the historical town since centuries. In order to describe the structural features driving these slope instability phenomena, a complete Terrestrial Laser Scanner (TLS) survey all around the San Leo cliff was performed. Moreover, Close-Range Photogrammetric (CRP) surveys and conventional geomechanical surveys on scanlines have been carried out. The 3D geometry of the cliffs was extracted and critical areas have been investigated in detail using dense Digital Surface Models (DSMs) obtained from CRP or TLS. The results were used to define the structural features of the plateau, to recognize more fractured areas, and to perform kinematic analyses, in order to assess the joint sets predisposing to slope instability at the cliff scale. The creation of a 3D model was also fundamental for the implementation of the geological model to be used in numerical modelling for hydrogeological characterization and slope stability analyses

THE COMPLEX OF SANTA CROCE IN RAVENNA AS A CASE STUDY: INTEGRATION OF 3D TECHNIQUES FOR SURVEYING AND MONITORING OF A HISTORICAL SITE

Over the last decades, climate change has brought more and more challenges to managers of cultural heritage and researchers. The increasing effects of natural hazards on assets have required the development of a new protocol of techniques and methodologies for the monitoring of Cultural Heritage and the adoption of management plans adapted to the new challenges at every stage of risk management. The work here presented aims at providing an insight of the work undertaken under the framework of the H2020 SHELTER project, to showcase the first steps of the multi-disciplinary research conducted in one of the project’s case studies, the complex of Santa Croce in Ravenna, Italy. The paper provides the presentation of the case study and the description of the surveying activities with some first results, to provide a preliminary assessment of the site criticalities to be addressed in the future activities in the area, in line with the EU project expected outcomes

Saving temporary exhibitions in virtual environments: The Digital Renaissance of Ulisse Aldrovandi – Acquisition and digitisation of cultural heritage objects

As per the objectives of Project CHANGES, particularly its thematic sub-project on the use of virtual technologies for museums and art collections, our goal was to obtain a digital twin of the temporary exhibition on Ulisse Aldrovandi called “The Other Renaissance”, and make it accessible to users online. After a preliminary study of the exhibition, focusing on acquisition constraints and related solutions, we proceeded with the digital twin creation by acquiring, processing, modelling, optimising, exporting, and metadating the exhibition. We made hybrid use of two acquisition techniques to create new digital cultural heritage objects and environments, and we used open technologies, formats, and protocols to make available the final digital product. Here, we describe the process of collecting and curating bibliographical exhibition (meta) data and the beginning of the digital twin creation to foster its findability, accessibility, interoperability, and reusability. The creation of the digital twin is currently ongoing

Monumentations of control points for the measurement of soil vertical movements and their interactions with ground water contents

Historically, one of the techniques used in the study of vertical movements of soil is that of high precision spirit levelling. Nowadays, this technique is often accomplished by satellite interferometric synthetic aperture radar (SAR) analysis that requires a calibration phase, i.e. through the connection to a spirit levelling network or by means of a long time series acquired by global navigation satellite systems permanent stations in order to transform relative velocities derived by SAR in absolute terms. An important aspect of this process consists of the materialization of the object used as a control point, while its selection may depend on the geological context. Typically, due to the inevitably high cost of installation, very accurate monumentation is reserved only for a limited density of points on the territory; therefore, a type of negative correlation exists, in terms of reliability in the monumentation of the control points, with respect to their density in a real distribution within a specific monitoring technique. For example, in levelling networks, a density of one benchmark every 700-1000 m of line is often desired in order to reach a compromise among costs, practical operative requirements and precision. Levelling benchmarks are usually fixed on existing structures (i.e. buildings or concrete structures). This aspect is even more evident in the case of SAR interferometric analysis, where the persistent scatterers (PS) are identified based on the coherence in the radar response. Therefore, the PS display movements are measured by a variety of different structures, characterized by foundations fixed at different depths.Starting from repeated levelling measurements, we verified the order of magnitude of movements of control points characterized by shallow foundations in cohesive soils. In practice, we observed their behaviour in relation to the depth of the foundation under simple and very common conditions, such as the presence of periods of drought or rainfall. The results indicate movements in the order of 3-7 mm in the first metre of depth that occurred in a week during the transition between the period of summer drought and the first rains. The magnitude of the total uplift observed between the end of the summer drought and the beginning of successive springtime (30/08/2012-18/04/2013) exceeded 10 cm of movement in very shallow layers of the soil surface for the same test field. © 2014 © 2014 Taylor & Francis