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Abstract. The Borobudur temple (Indonesia) is one of the greatest Buddhist monuments in the world, now listed as an UNESCO World Heritage Site. The present state of the temple is the result of restorations after being exposed to natural disasters several times. Today there is still a growing rate of deterioration of the building stones whose causes need further researches. Monitoring programs, supported at institutional level, have been effectively executed to observe the problem. The paper presents the latest efforts to digitally document the Borobudur Temple and its surrounding area in 3D with photogrammetric techniques. UAV and terrestrial images were acquired to completely digitize the temple, produce DEM, orthoimages and maps at 1:100 and 1:1000 scale. The results of the project are now employed by the local government organizations to manage the heritage area and plan new policies for the conservation and preservation of the UNESCO site. In order to help data management and policy makers, a web-based information system of the heritage area was also built to visualize and easily access all the data and achieved 3D results.

Abstract. The glaciers on the summit plateau of Kibo, the main peak of the Kilimanjaro massif (3°S, 37°E, 5895 m a.s.l.) in Tanzania, are characterized by steep ice cliffs at their margins. These form-persistent cliffs continuously retreat and, consequently, govern the decrease in plateau glacier area. In order to quantify the ice cliff recession and study their morphology, close-range terrestrial photogrammetry combined with automatic stereo matching techniques was used to derive high resolution digital surface models of a south-facing “sample cliff” at four different dates. Results confirm, firstly, the annually bimodal nature of the recession being 15 cm/month during a 4.5 month sunlit phase and 2 cm/month during the remaining 7.5 month shaded phase, and, secondly, the tendency towards an “ideal cliff orientation”, which is either south- or north-facing and about 70°-75° steep. Moreover, the hypothesis of a predefined decay period for the plateau ice is supported by this study and it is shown that terrestrial photogrammetry is not only cheap and lightweight but also very suitable for ice surveys at the decameter scale.

Abstract. The 3rd edition of the international summer school “Close-range Sensing Techniques in Alpine terrain” took place in Obergurgl, Austria, in June 2019. This article reports on results from the training and seminar activities and the outcome of student questionnaire survey. Comparison between the recent edition and the past edition in 2017 shows no significant differences on the level of satisfaction on organizational and training aspects. Gender balance was present both in candidates and in the outcome of selections. Selection was based on past research activities and on topic relevance. The majority of trainees were therefore doctoral candidates and postdoctoral researchers, but also motivated master students participated. The training took place through keynotes, lectures, seminars, in the field with hands-on surveys followed by data analysis in the lab, and teamwork for preparing a final team presentation over different assignments.

Abstract. In complex mountainous terrain the mapping efficiency is a crucial factor. Unmanned aerial vehicle (UAV) based laser scanning (ULS) has the capability for efficient mapping, as it allows realizing higher flight velocities, higher flying altitude above ground level (AGL) and larger distances between neighbouring flight strips, compared to image based techniques. However, fully utilising the efficiency of the system in mission planning (especially for complex terrain projects, where occlusions and differently inclined surfaces are present) is prone to miss the project requirements in terms of point density and strip overlap. Therefore, the numerical simulation of point densities is a helpful tool for realizing a reliable planning of scan coverage. We implemented a ray-tracing-based ULS-simulator, specifically designed for emulating the mechanism of a Riegl VUX-1LR laser scanner carried by a Riegl RiCOPTER. The simulator can consider copter and scanner motion, which makes it possible to generate synthetic scan data excluding or including the aircraft movement due to aerodynamics by using either planned trajectories from a flight planning software or recorded and post-processed trajectories from an inertial measurement unit (IMU). Laser shots are simulated by intersecting rays from the virtual scanner with a mesh-based digital surface model (DSM). The results show that the tool generates plausible synthetic laser point distributions. However, this is only the case, when aircraft aerodynamics are considered, as the effect of striping due to flight control corrections during the flight is very prominent. It can be shown that applying the presented tool for mission planning (without knowing the actual flight movements) has to consider an error margin of ±50pts/m2 in order to guarantee a compliance with the planned project requirements. Nevertheless, the consideration of terrain by a high resolution DSM, especially in complex terrain, improves the correlation between simulated and real point densities significantly.

Abstract. In order to meet the requirements of the European Water Framework Directive (EU-WFD), authorities face the problem of repeatedly performing area-wide surveying of all kinds of inland waters. Especially for mid-sized or small rivers this is a considerable challenge imposing insurmountable logistical efforts and costs. It is therefore investigated if large-scale surveying of a river system on an operational basis is feasible by employing airborne hydrographic laser scanning. In cooperation with the Bavarian Water Authority (WWA Weilheim) a pilot project was initiated by the Unit of Hydraulic Engineering at the University of Innsbruck and RIEGL Laser Measurement Systems exploiting the possibilities of a new LIDAR measurement system with high spatial resolution and high measurement rate to capture about 70 km of riverbed and foreland for the river Loisach in Bavaria/Germany and the estuary and parts of the shoreline (about 40km in length) of lake Ammersee. The entire area surveyed was referenced to classic terrestrial cross-section surveys with the aim to derive products for the monitoring and managing needs of the inland water bodies forced by the EU-WFD. The survey was performed in July 2011 by helicopter and airplane and took 3 days in total. In addition, high resolution areal images were taken to provide an optical reference, offering a wide range of possibilities on further research, monitoring, and managing responsibilities. The operating altitude was about 500 m to maintain eye-safety, even for the aided eye, the airspeed was about 55 kts for the helicopter and 75 kts for the aircraft. The helicopter was used in the alpine regions while the fixed wing aircraft was used in the plains and the urban area, using appropriate scan rates to receive evenly distributed point clouds. The resulting point density ranged from 10 to 25 points per square meter. By carefully selecting days with optimum water quality, satisfactory penetration down to the river bed was achieved throughout the project. During the data processing meshes for multiple purposes like monitoring sediment transport or accumulation and hydro-dynamic numeric modeling were generated. The meshes were professionally conditioned considering the adherence of, both, geometric and physical mesh quality criterions. Whereas the research is focused on the design and implementation of monitoring database structures, the airborne hydrographic data are also made available for classical processing means (cross sections, longitudinal section).

Abstract. The ancient mining landscape of Schwaz/Brixlegg in the Tyrol, Austria witnessed mining from prehistoric times to modern times creating a first order cultural landscape when it comes to one of the most important inventions in human history: the production of metal. In 1991 a part of this landscape was lost due to an enormous landslide that reshaped part of the mountain. With our work we want to propose a digital workflow to create a 3D semantic representation of this ancient mining landscape with its mining structures to preserve it for posterity. First, we define a conceptual model to integrate the data. It is based on the CIDOC CRM ontology and CRMgeo for geometric data. To transform our information sources to a formal representation of the classes and properties of the ontology we applied semantic web technologies and created a knowledge graph in RDF (Resource Description Framework). Through the CRMgeo extension coordinate information of mining features can be integrated into the RDF graph and thus related to the detailed digital elevation model that may be visualized together with the mining structures using Geoinformation systems or 3D visualization tools. The RDF network of the triple store can be queried using the SPARQL query language. We created a snapshot of mining, settlement and burial sites in the Bronze Age. The results of the query were loaded into a Geoinformation system and a visualization of known bronze age sites related to mining, settlement and burial activities was created.