371 research outputs found
Introduction to mobile mapping with portable systems
No full textPortable mobile mapping systems (PMMSs) are an emerging technology, increasingly employed in different application fields. Their distinctive feature is the ability to acquire 3D information on-the-move, and, unlike vehicle-based MMSs, the possibility to efficiently document narrow, indoor and confined environments. The present chapter provides an overview of PMMSs, with a taxonomy of the available platforms and a description of hardware components and data processing algorithms. A review about 3D quality assessment and typical applications is also reported, with the aim of providing readers with the basic knowledge and understanding of potentialities and challenges of this promising technology
A six month high resolution 4D geospatial stationiary laser scan dataset of the Kijkduin beach dune system, The Netherlands
No full textIn Kijkduin (The Netherlands) a Riegl terrestial laserscanner on top of a building has surveyed a kilometer of beach and dune from November 2016 to May 2017. More than 4000 hourly and daily scans were obtained during this period containing between 1 and 10 million points per epoch with a decimeter order point spacing and centimeter order vertical accuracy. The dataset was collected within the CoastScan project [Vos, S., Lindenbergh, R. & Vries, S. de. (2017) 'Coastscan :Continuous monitoring of coastal change using terrestrial laser scanning'. Coastal Dynamics, Denmark, 12–16 June 2017 ] which aims to study the natural variability and resilience of the coast and the use of near-continuous laserscanning to study various spatiotemporal processes simultaneously. The dataset contains 4082 individual scans with supporting files to obtain georeferenced and time corrected point clouds in the Dutch national coordinate system
Classifying Mangroves in Vietnam using Radar and Optical Satellite Remote Sensing: Processing Sentinel-1 and Sentinel-2 Imagery in Google Earth Engine
No full textMangroves are forest ecosystems growing in (sub)tropical saline coastal environments. With their unique root structure they serve as important natural coastal protection and provide habitats with excellent conditions for cultivating fish, shrimp and crab species. Despite all benefits mangrove forests are disappearing at alarming rates around the world but especially in Asia such as the Mekong Delta coast. Therefore, this research focusses on the Ca Mau Province in Vietnam. The Ca Mau province is the southernmost province of Vietnam with mangroves present along the coastlines, the Mui Ca Mau National Park and in mixed mangrove aquaculture farms. Remote sensing has been widely proven to be essential in mapping mangrove ecosystems. Previous research used either expensive optical and radar data sources or free but lower resolution systems. This study is the first that uses the new Copernicus Sentinel-1 radar and Sentinel-2 multispectral satellite missions that provide free available data with high spatial (10-20 meter) and temporal (10-12 days) resolution. Since optical data is prone to cloud effects and radar data is hard to interpret, both data sets are combined to investigate improvements for classifying mangroves. The data is processed in the new online Google Earth Engine platform providing a powerful tool for big data applications such as land cover classification. Optical data is found to separate mangroves by their spectral reflectance mainly in the near-infrared wavelength domain. The dominant mangrove species in the Ca Mau province, Rhizophora Apiculata and Avicennia Alba, are found to be separable from comparing unsupervised clustering results with ground truth locations. The C-band radar signal is dominated by volume scattering, indicating the density of the canopy. Especially VV-polarization has good correlation with canopy parameters. To improve information from the radar signal a temporal analysis is executed. Seasonal variations are quantified and show an increase according to the spatial succession of mangroves. Pioneer species, such as Avicennia genus, show less seasonal variations than mature species, such as Rhizophora genus. With the previous information five classes are defined: urban area, water and three mangrove classes: Rhizophora Apiculata species in extensive shrimps, Rhizophora Apiculata species in natural environment and Avicennia Alba species. A classification method is set-up in the Google Earth Engine with a Random Forest classifier using the satellite data inputs and ground truth training input of the five classes. A combination of the optical data with the temporal information of the radar data is found to be the best data input for separating those five classes. Classification results are obtained for discriminating mangrove types up to an overall accuracy of 87\%. The classification gets less reliable when mangrove species are mixed or at locations where the ground truth training input was scarce. With the resulting yearly land cover maps land cover changes can be detected. Comparing the land cover map of 2017 with a mangrove cover product of 2000 shows a regression along the southern coastline. No significant changes inside the shrimp farms are found between 2016 and 2017 but with the future availability of a long time series of Sentinel-1 and 2 data those can be detected with the method that is resulted from this study.Applied Earth Science
Distributed processing of Dutch AHN laser altimetry changes of the built-up area
No full textThe evolution and spreading of data capturing methods ranging from simple GPS devices like smart-phones to large scale imaging equipment – including very high resolution and hyperspectral cameras and LiDAR – resulted in an exponential growth in the amount of spatial data maintained by companies and organizations. At the same time methods for extracting information from such data are often behind in efficiency. In this paper we analyse the possibilities for nation-wide change detection of massive airborne laser altimetry point clouds, based on digital elevation models generated from them. The proposed workflow distinguishes modifications in the built-up area from other changes and noise. Our methodology combines different area processing spatial algorithms: object detection, noise filtering, morphological operations and clustering. Our proposed method is designed to scale dynamically on extensive datasets by processing a spatially partitioned input dataset in an easily parallelized manner. Favourable visualizations and aggregated representations of the results are examined, followed by a discussion of feasible validation methods. As a demonstration we showcase the implemented distributed evaluation of our workflow on the full Dutch altimetry archive – a dataset exceeding several terabytes of storage space – using a high-performance computing environment. While the average execution time was 47 h on a desktop computer, our solution only took less than 2.4 h to complete. The output was validated against the building layer of the TOP10NL topographic dataset, proving a 70% accuracy nation-wide and over 90% for urban areas. As a result our analysis shows that The Netherlands experienced an aggregated building volume change of 912.33 km3 between the acquisition of AHN-2 and AHN-3
Methods For Feature Extraction of an Outcrop Using Terrestrial LiDAR: Methods For Feature Extraction of an Outcrop Using Terrestrial LiDAR
No full textThe following report brings to light how LiDAR data of an outcrop can be acquired and subsequently processed in order to extract the geometry of the outcrop and its pertaining parameters. It makes the use of a sandstone outcrop in the Trooz quarry, Belgium, near Liege. The outcrop was scanned using a terrestrial laser scanner, after which the point cloud data recorded information, pertaining to position and intensity was then processed and subject to interpretation. The report aims to systematically and chronologically take the reader through the entire workflow used by the author, its drawbacks and advantages. Whilst providing a specific analysis of the outcrop in question, creating a general guideline is also an aim. Prior to the processing the significance of the geologic history of the area is touched upon along with the practical acquisition of that data, concerning equipment and procedure. The physical principles of LiDAR and other possible options of acquiring data such as photogrammetry are explained, each with their benefits and shortcomings. The practicality of LiDAR is especially analysed followed by explanation and usage of processing methods such as registration, geo-referencing and computation of geometrical parameters, specifically with the help of software’s such as CloudCompare and MATLAB. Once the results of such parameters are derived, their integrity is discussed by comparing MATLAB oriented methods to those of CloudCompare. These quantified results include values of dip angle and direction over the entire outcrop and the corresponding normal vectors. Varying roughness over the surface of the outcrop and analysis of the intensity distribution present. Whilst also validating these results by comparing them with manual recorded results of dip angle and direction taken at the site. The significance of these parameters is discussed and their application in the characterization of layering. Finally, suggestions regarding the methodology both during acquisition and processing such as during geo-referencing are made by displaying obstacles encountered and flaws realized in the author’s own work.Applied Earth Science
Contribution of Geosciences in the Study of Anthropogenic Activities in Different Temporal and Spatial Contexts
No full textFrom Homo sapiens, anthropogenic activities have impacted Earth systems at different spatial and time scales, particularly since the mid-twentieth century as the geological record confirms. Such impact has triggered Earth system counter reactions that threaten living species on Earth (including humans), the environment, modern infrastructure, and cultural heritage. Studying and understanding the spatial and temporal interactions between humans and Earth systems is critical in informed decision-making to prevent and mitigate the potential threats.
This thesis proposes a methodological approach for studying the interaction between humans and Earth systems in three different contexts: geohazards, archaeology, and urban planning. We focus on the holistic integration of techniques used in geosciences to generate seamless models of the Earth surface and subsurface, enabling the study of the footprint of anthropogenic processes in the geologic record and in the natural landscape. These techniques have limitations, though they are complementary. In this thesis, we aim to provide technical solutions to fill knowledge gaps when integrating such techniques in the generation of holistic models. This research encompasses multidisciplinary investigations including remote sensing, geophysics, geotechnics, geology, 3D modelling, and geographic information systems (GIS). Studies were conducted in Austria, Greece, and Norway, and are summarized in four journal articles.
The first article is within the geohazards context, and notably considers landslides. The study tests the performance of three well-known ground filtering algorithms when applied to laser scan data of an area with active landslides in the Austrian Alps. Most importantly, it assesses the impacts of each algorithm on the quantification of the surface deformation induced by landslides through time. Results of the study suggest that the choice of the ground filtering algorithm and its parameterization have effects when quantifying volume changes of landslides.
The second and the third articles were developed under the archaeological context. The second article promotes the digital documentation of threatened archaeological sites through the combination of remote sensing and structural geology. High resolution terrestrial laser scan data was used to generate an architectural catalogue of the Late Bronze Age (LBA) Mycenaean cemetery of Aidonia, Greece. The catalogue consists of a 3D model of chamber tombs carved in the natural rock formation and tables providing 208 architectural and geological measurements. Article III builds on article II and proposes two methods for the semi-automatic identification and mapping of linear features such as chisel marks in the high-resolution laser scan data.
Multidisciplinary studies of article IV were conducted in the urban context of the city of Stavanger, Norway. The article focuses on the integration of laser scan data, aerial imagery, geotechnical and ground water drilling, ground penetrating radar (GPR), and geological outcrops to generate a holistic 3D model aimed to: i) study the distribution and composition of natural and non-natural materials on the surface and near-subsurface; ii) unravel the geological history of the area since the last ice age; and iii) determine significant topographic changes that occurred in the area, particularly those induced by anthropogenic activities.
This thesis proves that multidisciplinary approaches that integrate different techniques applied in geosciences are efficient for studying interconnected anthropogenic and geological phenomena at local and regional scales, and at different windows of time. The results of this research can be applied worldwide in future studies in the geohazards, archaeology, and urban planning contexts. Holistic models contribute to closing the knowledge gap between what can be seen on the surface and what cannot be seen in the subsurface
CLOSE-RANGE SENSING TECHNIQUES IN ALPINE TERRAIN
No full textEarly career researchers such as PhD students are a main driving force of scientific research and are for a large part responsible for research innovation. They work on specialized topics within focused research groups that have a limited number of members, but might also have limited capacity in terms of lab equipment. This poses a serious challenge for educating such students as it is difficult to group a sufficient number of them to enable efficient knowledge transfer. To overcome this problem, the Innsbruck Summer School of Alpine Research 2015 on close-range sensing techniques in Alpine terrain was organized in Obergurgl, Austria, by an international team from several universities and research centres. Of the applicants a group of 40 early career researchers were selected with interest in about ten types of specialized surveying tools, i.e. laser scanners, a remotely piloted aircraft system, a thermal camera, a backpack mobile mapping system and different grade photogrammetric equ..
Training In Innovative Technologies For Close-Range Sensing In Alpine Terrain
No full textThe 2nd international summer school "Close-range sensing techniques in Alpine terrain" was held in July 2017 in Obergurgl, Austria. Participants were trained in selected close-range sensing methods, such as photogrammetry, laser scanning and thermography. The program included keynotes, lectures and hands-on assignments combining field project planning, data acquisition, processing, quality assessment and interpretation. Close-range sensing was applied for different research questions of environmental monitoring in high mountain environments, such as geomorphologic process quantification, natural hazard management and vegetation mapping. The participants completed an online questionnaire evaluating the summer school, its content and organisation, which helps to improve future summer schools
Indentifying glacial features with sentinel-2 data
No full textThe Tibetan Plateau is a vast elevated plateau in Central and East Asia. It contains thousands of glaciers and other geographical features. Through this area rivers like the Brahmaputra is flowing and making a basin providing about millions of people a home. The last years global warming has been a focus of public and scientific debate. Not knowing what to expect and what the changes are result in ruling uncertainties which are of major concern because it could cause serious implications for water resources. During this study the area located in the Upper Brahmaputra in the South-East of the Tibetan Plateau called the Yiong Zangbu catchment will be investigated. To understand what glacial changed have occurred in the past few years data from different years were collected, processed and compared. The used datasets are ASTER GDEM, HydroSHEDS, GLIMS glacier mask and Sentinel-2 . Sentinel-2 data has been processed and different images are made like true colour and false colour images. Next to that a combination of datasets are used to see whether there is an accuracy issue and to understand what kind of features can be found on which height and what spectral reflectance belongs to it. After processing all the data of two following years differences can be seen. There are lakes that are frozen out within three months. Also glaciers which expanded downwards the hills. This can be a result of strong winters. On the higher parts there was more precipitation, which is helpful while remaining the current glaciers. <br/
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