Frank Steinbacher 1. aerial (approx. < 10 cm/pixel) waterbody and foreland survey.

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1 Frank Steinbacher 1 Combining novel and traditional survey technologies in water engineering: Airborne Hydromapping and sonar data of the Rhine River at Rheinfelden, Germany & Switzerland Frank Steinbacher, AirborneHydroMapping, Innsbruck, Austria Ramona Baran, AirborneHydroMapping, Innsbruck, Austria Markus Aufleger, Unit of Hydraulic Engineering, University Innsbruck, Austria How high-resolution bathymetric surveys will change the work and research on waterbody related topics Repetitive surveying of inshore waters and coastal zones is becoming more and more essential to evaluate water-level dynamics, structure and zone variations of rivers and riparian areas, river degradation, water flow or reservoir sedimentation, and coastal processes. This can only be achieved in an effective way by employing hydrographic airborne laser scanning (hydromapping). A new laser scanner for the acquisition of highresolution hydrographic data dedicated for surveying inland waters and shallow coastal zones is introduced. Figure 1: Underwater dune structures, shoreline Baltic Sea Measurement results obtained with the compact airborne laser-scanning system at the river Rhine, including the shallow areas up to 3 m depth, riparian areas and one of the largest fish passes are presented in combination with sonar information for deeper areas. For the first time, a high resolution spatial view on the ground of the water body is possible (approx points/m²), and the data combined with high resolution Figure 1: The classic and complex procedure of aerial (approx. < 10 cm/pixel) waterbody and foreland survey. or spectral images offer a variety of new opportunities for further analysis. The combination of these datasets (all of them captured during a single flight including

2 2 Combining novel and traditional survey technologies in water engineering: Airborne Hydromapping and sonar data of the Rhine River at Rheinfelden, Germany & Switzerland topography, bathymetry, aerial and spectral pictures) provide a comprehensive and homogeneous data basis for a detailed and precise description of river bed hydraulic, morphologic and ecohydraulic processes. The high density and accuracy of information offer the extended possibility for monitoring and supervisory aspects. Figure 2: Shallow areas captured by hydromapping, deeper areas captured by echo sounder. 1. Fields of application 1.1 Engineering For water engineering one of the most important aspects of hydraulic deals with representing the topography of rivers, floodplains, estuaries or coastal areas. Although different fields of impact characterizing the hydraulic background of water bodies (e.g. 2dor 3d-modeling) is one main effort, the difference of the required hydraulic set-up can be found in scale and resolution for appropriate modelling but all of them need to work on close-to-reality numerical models. Commonly, flood or wave model applications utilize digital elevation models based on high-quality and high-resolution topographic airborne laser data. The digital elevation model of a water body itself is normally represented by simplified and interpolated data based on cross-sections, manually collected during terrestrial fieldwork or by echosounder data. Due to a lack of spatial and high-resolution water-body information, the modelling of shallow areas like meadows, estuaries, riverbanks or dune structures is highly time consuming, or even impossible. Frequent urban or coastal flooding over the past decades have identified an urgent need to improve and increase our modelling efforts, and to address more explicitly the focus on effects of uncertainty in simulations caused by model input data. Society demands reliable and detailed information on magnitude and likelihood of hazardous flood events to design flood mitigation. For this, the assumption of the shape

3 Frank Steinbacher 3 of the water body or manmade protection structures has to be solved and modelling improved by using the actual shape. Furthermore, additional information like surface roughness or the water surface are relevant to calibrate the models. The technology of hydromapping aims to solve this challenge. 1.2 Water Framework Directive and its political aims The EU Water Framework Directive (WFD) is a radical and ambitious agenda to protect and enhance the quality of aquatic ecosystems throughout Europe. It is fundamentally interdisciplinary in nature, as it places ecology at the heart of the management objectives. This means that its implementation is predicated on understanding the complex interactions between hydromorphological, physico-chemical, biological and human pressures expressed in terms of water bodies ecological statuses. Effective and sustainable implementation of the WFD requires a major commitment to develop new monitoring protocols and much better understanding of the biophysical linkages between anthropogenic pressures and their ecological response. Evidence to date indicates that many member states are struggling to meet their commitments in monitoring, and the introduction of schedules for remediation measures where water bodies are failing to meet the WFD objectives. With respect to the WFDs overall aim of cost-effective mitigation measures, datasets acquired by hydromapping will deliver a better understanding for eco-hydro-morphological processes by detecting new indicators and delivering advanced or new methods, combined with models, tools, software and services. This is seen as a precondition to the development of cost-effective and sustainable remediation of damaged ecosystems, and to future-proof the likely adverse impacts associated with climate change, which will influence water bodies in different regions in Europe in a myriad of ways. 1.2 Research Based on the complexity of a bathymetric survey system, a task distribution between an industrial partner (RIEGL Laser Measurement Systems) and a research institute (Unit of Hydraulic Engineering of the University Innsbruck) was required. While the industrial partner was responsible for hardware development of the laser system, the academic partner was responsible for water related issues and verification. For this, the desired penetration depth, measurement resolution or accuracy were defined among other parameters, and special emphasis was always laid on the systems application for shallow waters. This approach constitutes a unique feature and will also be the future basis for the on-going research cooperation. Further research concerning the laser-scanner system includes hardware developments, experimental verification, data processing and software development as well as improving the survey process itself. Especially the new data quality provides the basis for a series of follow-up research projects referring to hydraulic, sediment or water ecology problems. Out of this, a significantly better understanding of the

4 4 Combining novel and traditional survey technologies in water engineering: Airborne Hydromapping and sonar data of the Rhine River at Rheinfelden, Germany & Switzerland process of sediment transport or an improved possibility for modeling habitats can be expected. In the future, a series of university institutions will be active in the domain of these themes. At the moment, the Unit of Hydraulic Engineering deals among others with the possibility to improve hydraulic modeling based on the new hydromapping data. Based on the complexity of the bathymetric data and the information contained (e.g. turbidity, velocity, waves), the necessity for new analysis and visualization tools resulted in software development activity regarding the new data within the frame of an academic research group. 2. Hydromapping project work Figure 3: Principle of the hydromapping technology. Airborne laser scanning is unique, because it is the most effective concept for fast and economic mapping of large or recurring areas as well as collecting up-todate, high-quality, and highresolution survey data. Recent developments at the Unit of Hydraulic Engineering of the University of Innsbruck in cooperation with RIEGL LMS allows for the first time to conduct comprehensive surveys of shallow water bodies using an airborneoperated water-penetrating laser system (airborne hydro-mapping; Fig. 3).

5 Frank Steinbacher 5 The potential and great benefit of this technology is the opportunity to survey flowing waters, shallow areas of reservoirs and near-shore areas in short intervals with an accuracy and information density that can be compared to topographic laser scanning. Moreover, monitoring of changes is possible for the first time. The scope is to offer a data basis for water engineering and short-dated economic and political decisions by a cost effective measurement method. The fields of application are tremendous and placed in the field of hydraulics, hydro-morphology, hydro-ecology, restoration or hydropower. Figure 4: Integration of the hydromapping technology within fixed wing aircraft and helipod In cooperation with the hydropower operator Energiedienst AG, Germany, a survey project at the new hydropower plant Rheinfelden was initiated. A project area of about 6 km was captured; including high-resolution aerial images (~5 cm/pixel) to provide an optical reference and offering a wide range of possibilities for subsequent research, monitoring, and management. The field of view of the aerial camera covered slightly more than the swath width of the laser scanner. The airspeed of the fixed wing aircraft was about 75 kts. Figure 5: DEM and extracted water surface The survey of 6 km river was performed in April 2012 and took 2 hours in total. The data acquisition by fixed wing aircraft was conducted from an altitude of about 600 m with a pulse repetition rate of 250 khz and a maximum laserpulse energy still maintaining eye-safety even for the aided eye. While depths of up to 3 m

6 6 Combining novel and traditional survey technologies in water engineering: Airborne Hydromapping and sonar data of the Rhine River at Rheinfelden, Germany & Switzerland in the turbid Rhine river were obtained and the deeper areas combined with echo sounder data, it was even more important to assess the system performance in complex situations, i.e. fish pass structures, bed rock structures or underwater technical objects. The resulting point density ranged from 20 to 40 points per square meter. Figure 6: fish pass and technical structures at the hydropower plant Rheinfelden. Data processing further comprises the generation of different derivatives of the raw point cloud and RGB images as coloured pointcloud-, mesh- and GIS-datasets. Data from terrestrial surveys were used to calibrate the processed point cloud. For data comparison reasons echosounder data were captured by the authority at almost the same time (January and Mai 2012). While in the past gross estimates had to be used for analyzing underwater information, we now even face the problem of decimating the high-resolution information by filtering. It is one of the research fields at the Unit of Hydraulic Engineering of the University of Innsbruck to design filter algorithms, which not only observe the numerical and performance limitations of existing models but simultaneously provide improvements on the quality and usability of the results. The data processing strategy is motivated by the demand of end users to have a new data basis, from which to extract basic information on a daily basis without being forced to handle large pointcloud datasets.

7 Frank Steinbacher 7 The accuracy of the project was evaluated by comparing the laser-scan data with groundsurveyed reference surfaces and echosounder data. The system s error range is on the order of ± 5 cm, similar to conventional topographic airborne scanners compared to the reference surfaces. In contrast to traditionally terrestrial survey information or data captured from echosounder systems, even small-scale bed structures could be captured by the new highresolution survey method. The reduction of absolute point accuracy compared to terrestrially gained measurements is more than compensated by the overall accuracy arising from spatial point information information bringing up a three-dimensional thinking of under-water conditions, and enabling a successful and efficient monitoring of water bodies. Being able to identify all structures relevant to the flow or habitat units from a single fly-by is an amazing progress. With the new airborne hydromapping LIDAR sensor, it is for the first time possible to describe higher order hydrographic features and their spatial context. Information on hydraulic or ecologic underwater features as derivatives of distance, slope, curvature, area, or volume can be gained. Evaluation of the data captured in the course of the project as well as the development of corresponding tools to extract the information required to fulfill the EU-WFD is still in progress. 3. Conclusion and outlook The great importance of waterbody monitoring is underlined by problems concerning climate changes, flood protection, ecology, management of sediment, hydro power or problems of water ways. There is not only a direct need for such new data and their evaluation, facts and open questions concerning our waters will accompany mankind throughout the next decades. The new hydromapping approach is unchallenged with the opportunity to acquire high resolution survey information on the hydrographic, topographic and vegetation structures of shallow water bodies on a large scale. Airborne hydromapping delivers for the first time the required data to understand the complex interactions between hydromorphological, physico-chemical, biological and human-induced factors. An up-to-date, spatial, and integrative monitoring approach enabled by laser-scan data and the subsequent analysis of the ecological impact meets the requirements to handle present and future demands on our water bodies. Including the registered GreenSurvey technique for data capturing even the CO2-footprint of the project is unbeatable compared to other methods. Also the silent and undisturbing survey method made it possible to capture the entire data without interacting with other human activities along the river.

8 technique f 8 Combining novel and traditional survey technologies in water engineering: Airborne Hydromapping and sonar data of the Rhine River at Rheinfelden, Germany & Switzerland Figure 7: High-resolution results of underwater relief and technical structures. Pointcloud visualized in HydroVISH (software package especially dedicated to the combined analysis of topographic and bathymetric information) As already mentioned especially monitoring tasks require a combined analysis of all datasets related to the river shallow water areas. This provides a more comprehensive understanding of the actual condition, and thus allows the identification of changes associated with our water bodies. In order to facilitate these analysis, the lidar data could be combined with echosounder data, RGB or hyperspectral images. Due to the fact that besides data capturing data processing and evaluation is a fundamental part of water surveys, also high effort needs to be imposed on software and technical engineering tasks.

9 Frank Steinbacher Figure 8: Upstream view to hydropower plant, fish pass and bed rock structures Figure 9: DEM build on hydromapping and sonar data 9

10 10 Combining novel and traditional survey technologies in water engineering: Airborne Hydromapping and sonar data of the Rhine River at Rheinfelden, Germany & Switzerland 4. References Pfennigbauer M., Steinbacher F., Aufleger M., A novel approach to laser-based hydrographic data acquisition, ELMF, (2010). Steinbacher F., Pfennigbauer M., Aufleger M., Ullrich A., AirborneHydroMapping Area wide surveying of shallow water areas, Proc. of 38th ISPRS Congres, ISPRS, (2010) Pfennigbauer M., Steinbacher F., Ullrich A., Aufleger M., High resolution hydrographic airborne laser scanner for surveying inland waters and shallow coastal zones, Proc. of SPIE 8037, , Orlando (2011) Steinbacher F., Pfennigbauer M., Progress report Austrian Research Promotion Agency (FFG), FFG, (2009) Ressla C., Mandlburger G., Pfeifer N., Investigating adjustment of airborne laser scanning strips without usage of GNSS/IMU trajectory data, (2009) Hauer C., Mandelburger G., Habersack H., Hydraulically related hydro- morphological units: description based on a new conceptual mesohabitat evaluation model (mem) using lidar data as geometric input., River Research and Applications 25, 2947 (2009)