Michael Doneus

Openness as Visualization Technique for Interpretative Mapping of Airborne Lidar Derived Digital Terrain Models

Openness is proposed as a visualization technique for the archaeological interpretation of digital terrain models derived from airborne laser scanning. In contrast to various shading techniques, openness is not subject to directional bias and relief features highlighted by openness do not contain any horizontal displacement. Additionally, it offers a clear distinction between relief features and the surrounding topography, while it highlights both the highest and lowest parts of features. This makes openness an ideal tool for mapping and outlining of archaeological features. A comparison with sky-view factor and local relief model visualizations helps to evaluate advantages and limits of the technique.

Digital terrain modelling for archaeological interpretation within forested areas using full-waveform laserscanning

The identification of sites within forested areas is one of the remaining unresolved issues for archaeological prospection. Airborne laser scanning can be a solution to this problem: due to the capability of penetrating forest to a certain degree (depending on the vegetation density) the determination of the terrain surface is even possible in wooded areas. To be able to identify archaeological structures, archaeologists have to interpret the resulting topographical data of a filtered ALS scan. This does not pose major problems with large structures. Smaller features, however, are much more difficult to identify, because their appearance in an ALS point cloud is very similar to natural and recent features, as for example dense brushwood, or piles of twigs or wood. Therefore, to eliminate potential sources of error, a high quality separation of terrain and off-terrain points is essential for archaeological interpretation while maintaining a high point density of the ALS data. Using conventional ALS systems, the possibilities to classify terrain and off-terrain points are limited and the results - especially in forested areas with dense understorey - are far from ideal for archaeological purposes. This paper will demonstrate how the new generation of full-waveform ALS systems can be used to get a much better classification of solid ground and vegetation cover and consequently DTMs, which can be interpreted archaeologically with much more confidence.

Identification of roof areas suited for solar energy conversion systems

The basis for the determination of the solar potential is the identification and classification of areas suited for the use of solar energy conversion systems. By means of photogrammetry the roofs of the buildings in Viennas eighth district are measured with respect to their position, size, inclination and azimuth. The stored data are further processed in order to obtain the average local solar potential. The results are discussed with respect to their relevance to the technical solar potential.

ARCTIS — A MATLAB® Toolbox for Archaeological Imaging Spectroscopy

Imaging spectroscopy acquires imagery in hundreds or more narrow contiguous spectral bands. This offers unprecedented information for archaeological research. To extract the maximum of useful archaeological information from it, however, a number of problems have to be solved. Major problems relate to data redundancy and the visualization of the large amount of data. This makes data mining approaches necessary, as well as efficient data visualization tools. Additional problems relate to data quality. Indeed, the upwelling electromagnetic radiation is recorded in small spectral bands that are only about ten nanometers wide. The signal received by the sensor is, thus quite low compared to sensor noise and possible atmospheric perturbations. The often small, instantaneous field of view (IFOV)—essential for archaeologically relevant imaging spectrometer datasets—further limits the useful signal stemming from the ground. The combination of both effects makes radiometric smoothing techniques mandatory. The present study details the functionality of a MATLAB®-based toolbox, called ARCTIS (ARChaeological Toolbox for Imaging Spectroscopy), for filtering, enhancing, analyzing, and visualizing imaging spectrometer datasets. The toolbox addresses the above-mentioned problems. Its Graphical User Interface (GUI) is designed to allow non-experts in remote sensing to extract a wealth of information from imaging spectroscopy for archaeological research. ARCTIS will be released under creative commons license, free of charge, via website (http://luftbildarchiv.univie.ac.at).

The discovery of the school of gladiators at Carnuntum, Austria

Sophisticated techniques of archaeological survey, including airborne imaging spectroscopy, electromagnetic induction and ground-penetrating radar, are opening up new horizons in the non-invasive exploration of archaeological sites. One location where they have yielded spectacular results is Carnuntum in Austria, on the south bank of the Danube, capital of the key Roman province of Pannonia. Excavations in the late nineteenth and twentieth centuries revealed many of the major elements of this extensive complex, including the legionary fortress and the civilian town or municipium. Excavation, however, is no longer the only way of recovering and recording the details of these buried structures. In 2011, a combination of non-invasive survey methods in the area to the south of the civilian town, where little was visible on the surface, led to the dramatic discovery of remains interpreted as a gladiatorial school, complete with individual cells for the gladiators and a circular training arena. The combination of techniques has led to the recording and visualisation of the buried remains in astonishing detail, and the impact of the discovery is made all the greater by the stunning reconstruction images that the project has generated.

Undistorting the Past: New Techniques for Orthorectification of Archaeological Aerial Frame Imagery

Archaeologists using airborne data can encounter a large variety of frame images in the course of their work. These range from vertical aerial photographs acquired with very expensive calibrated optics to oblique images from hand-held, uncalibrated cameras and even photographs shot with compact cameras from an array of unmanned airborne solutions. Additionally, imagery can be recorded in one or more spectral bands of the complete optical electromagnetic spectrum. However, these aerial images are rather useless from an archaeological standpoint as long as they are not interpreted in detail. Furthermore, the relevant archaeological information interpreted from these images has to be mapped and compared with information from other sources. To this end, the imagery must be accurately georeferenced, and the many geometrical distortions induced by the optics, the terrain and the camera tilt should be corrected. This chapter focuses on several types of archaeological airborne frame imagery, the distortion factors that are influencing these two-dimensional still images and the necessary steps to compute orthophotographs from them. Rather than detailing the conventional photogrammetric orthorectification workflows, this chapter mainly centres on the use of computer vision-based solutions such as structure from motion (SfM) and dense multi-view stereo (MVS). In addition to a theoretical underpinning of the working principles and algorithmic steps included in both SfM and MVS, real-world imagery originating from traditional and more advanced airborne imaging platforms will be used to illustrate the possibilities of such a computer vision-based approach: the variety of imagery that can be dealt with, how (accurately) these images can be transformed into map-like orthophotographs and how these results can aid in the documentation of archaeological resources at a variety of spatial scales. Moreover, the case studies detailed in this chapter will also prove that this approach might move beyond current restrictions of conventional photogrammetry due to its applicability to datasets that were previously thought to be unsuitable for convenient georeferencing.

Prospecting archaeological landscapes

The future demands on professional archaeological prospection will be its ability to cover large areas in a time and cost efficient manner with very high spatial resolution and accuracy. The objective of the 2010 in Vienna established Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology in collaboration with its nine European partner organizations is the advancement of the state-of-the-art by focusing on the development of remote sensing, geophysical prospection and virtual reality applications, as well as of novel integrated interpretation approaches dedicated to non-invasive spatial archaeology combining cutting-edge near-surface prospection methods with advanced computer science. Within the institutes research program different areas for distinct case studies in Austria, Germany, Norway, Sweden and the UK have been selected as basis for the development and testing of new concepts for efficient and universally applicable tools for spatial, non-invasive archaeology. The collective resources and expertise available amongst the new research institute and associated partners permit innovative approaches to the archaeological exploration, documentation and investigation of the cultural heritage contained in entire archaeological landscapes. First promising results illustrate the potential of the proposed methodology and concepts.

Automated Archiving of Archaeological Aerial Images

The main purpose of any aerial photo archive is to allow quick access to images based on content and location. Therefore, next to a description of technical parameters and depicted content, georeferencing of every image is of vital importance. This can be done either by identifying the main photographed object (georeferencing of the image content) or by mapping the center point and/or the outline of the image footprint. The paper proposes a new image archiving workflow. The new pipeline is based on the parameters that are logged by a commercial, but cost-effective GNSS/IMU solution and processed with in-house-developed software. Together, these components allow one to automatically geolocate and rectify the (oblique) aerial images (by a simple planar rectification using the exterior orientation parameters) and to retrieve their footprints with reasonable accuracy, which is automatically stored as a vector file. The data of three test flights were used to determine the accuracy of the device, which turned out to be better than 1° for roll and pitch (mean between 0.0 and 0.21 with a standard deviation of 0.17–0.46) and better than 2.5° for yaw angles (mean between 0.0 and −0.14 with a standard deviation of 0.58–0.94). This turned out to be sufficient to enable a fast and almost automatic GIS-based archiving of all of the imagery.

Radiometric Information from Airborne Laser Scanning for Archaeological Prospection

Airborne laser scanning (ALS) is widely used for the sampling of large landscapes for different application areas. Since several years ALS data is also often used in archaeological prospection, e.g. in order to detect archaeological features beneath the vegetation canopy cover. For most of the applications only the geometric information provided by ALS is utilized. However, next to geometric information ALS provides radiometric information for each acquired point. For its practical usability radiometric calibration is essential. This contribution presents, next to the basic theory, a radiometric calibration workflow for ALS data. As a result calibrated spectral information is added to the ALS point cloud. This information can be used to generate images displaying reflectance at the wavelength of the ALS sensor. The presented calibration workflow is furthermore applied to different ALS missions carried out in the study area Carnuntum, Austria. Due to the usage of ALS sensors with different laser wavelength...

Utilization of full-waveform data in airborne laser scanning applications

Direct detection laser radar systems with echo signal digitization and subsequent full waveform analysis provide additional information on the targets properties compared to conventional discrete echo systems. We focus on the advantages of utilizing the additional information especially in the course of airborne laser scanning, improving for example the mandatory process for classifying the measurement data for generating high-quality digital terrain models. We present field data to demonstrate the superiority of full-waveform data over conventional laser data.