Synergistic exploitation of geoinformation methods for post-earthquake 3D mapping of Vrisa traditional settlement, Lesvos Island, Greece

The aim of this paper is to present the methodology followed and the results obtained by the synergistic exploitation of geo-information methods towards 3D mapping of the impact of the catastrophic earthquake of June 12th 2017 on the traditional settlement of Vrisa on the island of Lesvos, Greece. A campaign took place for collecting: a) more than 150 ground control points using an RTK system, b) more than 20.000 high-resolution terrestrial and aerial images using cameras and Unmanned Aircraft Systems and c) 140 point clouds by a 3D Terrestrial Laser Scanner. The Structure from Motion method has been applied on the high-resolution terrestrial and aerial photographs, for producing accurate and very detailed 3D models of the damaged buildings of the Vrisa settlement. Additionally, two Orthophoto maps and Digital Surface Models have been created, with a spatial resolution of 5cm and 3cm, respectively. The first orthophoto map has been created just one day after the earthquake, while the second one, a month later. In parallel, 3D laser scanning data have been exploited in order to validate the accuracy of the 3D models and the RTK measurements used for the geo-registration of all the above-mentioned datasets. The significant advantages of the proposed methodology are: a) the coverage of large scale areas; b) the production of 3D models having very high spatial resolution and c) the support of post-earthquake management and reconstruction processes of the Vrisa village, since such 3D information can serve all stakeholders, be it national and/or local organizations

Evolution of the settlements of Lesvos in the second half of the 20th century

The purpose of this doctoral thesis is to study the evolution of settlements, with a population of less than 2000 inhabitants, on the island of Lesvos, which is the study area, in the second half of the 20th century. This comparison is made based on three time points (1960, 1988, 1998) of the boundaries of settlements with a population of less than 2000 inhabitants, taking into account the aerial photographs of the H.M.G.S. of 1960, the boundaries established in these settlements with the P.D. 24-4 / 3-5-1984 D’ and the orthophoto maps of O.Η.Μ.C. year 1998. Most of these settlements pre-existed in 1923 and the definition of their boundaries is an important element for their development and evolution. To achieve this goal, GIS and Geoinformatics tools and techniques were used and the way in which they were used is analyzed in detail, in order to develop the methodology by which the questions posed were approached. To answer the questions, vector files of the borders were created at each time point, geographical databases, comparison tables, as well as maps for the visualization of the results. This doctoral study, which introduces innovative data in the recording, analysis and comparison of settlement development, can be a basis for future planning of their developmentΣκοπός της διδακτορικής αυτής εργασίας είναι να μελετήσει την εξέλιξη των οικισμών, με πληθυσμό μικρότερο από 2000 κατοίκους, στο νησί της Λέσβου, που αποτελεί τη περιοχή μελέτης, το 2ο μισό του 20ου αιώνα. Η σύγκριση αυτή πραγματοποιείται με βάση τρεις χρονικές στιγμές (1960, 1988, 1998) των ορίων των οικισμών με πληθυσμό μικρότερο από 2000 κατοίκους, λαμβάνοντας υπόψιν της αεροφωτογραφίες της ΓΥΣ του 1960, τα όρια που θεσπίστηκαν στους οικισμούς αυτούς με το Π.Δ. 24-4/3-5-1984 Δ΄ και τους ορθοφωτοχάρτες του Ο.Κ.Χ.Ε. του 1998. Οι περισσότεροι από τους οικισμούς αυτούς προϋπήρχαν του 1923 και ο καθορισμός των ορίων τους αποτελεί σημαντικό στοιχείο για την ανάπτυξη και την εξέλιξή τους. Για την επίτευξη του στόχου αυτού χρησιμοποιήθηκαν εργαλεία και τεχνικές ΣΓΠ και Γεωπληροφορικής και αναλύεται λεπτομερώς ο τρόπος με τον οποίο χρησιμοποιήθηκαν, για να αναπτυχθεί η μεθοδολογία με την οποία προσεγγίστηκαν τα ερωτήματα που ετέθησαν. Για την απάντηση των ερωτημάτων δημιουργήθηκαν διανυσματικά αρχεία των ορίων σε κάθε χρονική στιγμή, βάσεις γεωγραφικών δεδομένων, συγκριτικοί πίνακες, αλλά και χάρτες για την οπτικοποίηση των αποτελεσμάτων. Η διδακτορική μελέτη αυτή, που εισάγει καινοτόμα στοιχεία στην καταγραφή, την ανάλυση και την σύγκριση της εξέλιξης οικισμών, μπορεί να αποτελέσει βάση για τον μελλοντική σχεδιασμό της εξέλιξής τους

Building Change Detection Based on a Gray-Level Co-Occurrence Matrix and Artificial Neural Networks

The recovery phase following an earthquake event is essential for urban areas with a significant number of damaged buildings. A lot of changes can take place in such a landscape within the buildings’ footprints, such as total or partial collapses, debris removal and reconstruction. Remote sensing data and methodologies can considerably contribute to site monitoring. The main objective of this paper is the change detection of the building stock in the settlement of Vrissa on Lesvos Island during the recovery phase after the catastrophic earthquake of 12 June 2017, through the analysis and processing of UAV (unmanned aerial vehicle) images and the application of Artificial Neural Networks (ANNs). More specifically, change detection of the settlement’s building stock by applying an ANN on Gray-Level Co-occurrence Matrix (GLCM) texture features of orthophotomaps acquired by UAVs was performed. For the training of the ANN, a number of GLCM texture features were defined as the independent variable, while the existence or not of structural changes in the buildings were defined as the dependent variable, assigning, respectively, the values 1 or 0 (binary classification). The ANN was trained based on the Levenberg–Marquardt algorithm, and its ability to detect changes was evaluated on the basis of the buildings’ condition, as derived from the binary classification. In conclusion, the GLCM texture feature changes in conjunction with the ANN can provide satisfactory results in predicting the structural changes of buildings with an accuracy of almost 92%

Scale issues for geoheritage 3D mapping: The case of Lesvos Geopark, Greece

A geopark can be composed of many individual geosites of various geographical scales, thus, categorization according to cartographic scale is crucial for their 3D mapping. The UNESCO Global Geopark of the island of Lesvos in the north-east Aegean, Greece, is a distinctive example of this type of geopark as it contains many unique geosites that vary in geographical scale. The geographical scale is interconnected with the cartographic scale in which the geosite is visualized. The desired cartographic scale is an essential user requirement within an unmanned aerial vehicle's (UAVs) 3D mapping project as the basis for the data acquisition strategy. This research investigates the scale issues in 3D mapping of geosites. Furthermore, it contributes to the incorporation of the geographic and cartographical scales in association with UAV flight parameters such as Ground Sample Distance (GSD), altitude, gimbal pitch, orientation, and front and side overlapping. A total of 132 geosites located in Lesvos Geopark are being studied to determine the flight parameters of three different UAVs and their camera characteristics. The methodology followed to collect very high-resolution images suitable for 3D mapping consists of five main stages: i) determining the geographical scale of each geosite, ii) defining the cartographic scale of all geosites, iii) calculation of the GSD based on cartographic scale, iv) calculation of UAV flight altitude and flight characteristics, and v) classification of geosites based on the flight characteristics for their 3D mapping. Five geographic (G1: 100 ha) and five cartographic (C1: > 1:50, C2: 1:50–1:100, C3: 1:100–1:250, C4: 1:250–1:500, C5: < 1:500) categories were defined based on the geosites' size and extent. The combination of the two scales determines the most efficient flight characteristics and optimally acquires very high-resolution images required for the 3D mapping of the selected geosites. Finally, the categorization and characteristics of flights for data collection for high-resolution 3D mapping are collected and presented in a web application. The web application is addressed to the management board of Lesvos Geopark and supports the decision-making processes on mapping geosites using UAVs

Post-earthquake recovery phase monitoring and mapping based on UAS data

Geoinformatics plays an essential role during the recovery phase of a post-earthquake situation. The aim of this paper is to present the methodology followed and the results obtained by the utilization of Unmanned Aircraft Systems (UASs) 4K-video footage processing and the automation of geo-information methods targeted at both monitoring the demolition process and mapping the demolished buildings. The field campaigns took place on the traditional settlement of Vrisa (Lesvos, Greece), which was heavily damaged by a strong earthquake (Mw=6.3) on June 12th, 2017. For this purpose, a flight campaign took place on 3rd February 2019 for collecting aerial 4K video footage using an Unmanned Aircraft. The Structure from Motion (SfM) method was applied on frames which derived from the 4K video footage, for producing accurate and very detailed 3D point clouds, as well as the Digital Surface Model (DSM) of the building stock of the Vrisa traditional settlement, twenty months after the earthquake. This dataset has been compared with the corresponding one which derived from 25th July 2017, a few days after the earthquake. Two algorithms have been developed for detecting the demolished buildings of the affected area, based on the DSMs and 3D point clouds, correspondingly. The results obtained have been tested through field studies and demonstrate that this methodology is feasible and effective in building demolition detection, giving very accurate results (97%) and, in parallel, is easily applicable and suit well for rapid demolition mapping during the recovery phase of a post-earthquake scenario. The significant advantage of the proposed methodology is its ability to provide reliable results in a very low cost and time-efficient way and to serve all stakeholders and national and local organizations that are responsible for post-earthquake management