Author(s): Frank Steinbacher; Ramona Baran; Wolfgang Dobler; Markus Aufleger; Lutz Christiansen; Company
Linked Author(s): Markus Aufleger
Keywords: Irborne Hydromapping; Sonar; Baltic Sea; Coastal processes; Bathymetry
Abstract: The repetitive surveying of inshore waters and coastal zones is becoming more and more essential to evaluate water-level dynamics, structural and zonal variations of rivers and riparian areas, degradation and sedimentation, as well as coastal processes. This can only be achieved in an effective and comprehensive way by combining hydrographic airborne laser-scanning (hydromapping) and sonar measurements. Airborne Hydromapping is a new technology for the very detailed survey of rivers, lakes, reservoirs, and coastlines. This technique was developed within the scope of a research project between the University of Innsbruck and RIEGL LMS (Horn, Lower Austria). This airborne-operated, water-penetrating laser system is considered as a technical revolution for the comprehensive and simultaneous monitoring of shallow water bodies (depths down to 8 m), and the adjacent foreland with an accuracy of less than 10 cm. In contrast, sonar measurements are traditionally utilized to determine the deeper bathymetry of inland and marine water bodies (depths of 2 m down to more than 100 m). The combination of these two survey approaches is thus straightforward in order to efficiently capture the bathymetry of inland and marine waters across a broad depth range due to the overlap (between 2 m and 8 m). We present measurement results obtained with the compact airborne laser-scanning system along the Baltic Sea coast northeast of Kiel city, northern Germany, in July 2012. Here, we obtained measurement depths up to ca. 8 m under clear-water conditions that allow for a high-resolution spatial view on the ground of the water body (point density of ca. 10-20 points/m²). Moreover, we detect underwater dune-structures, and the accumulation of sediment within groin structures. The hydromapping data had been combined with simultaneously acquired sonar data that cover a depth range from approximately 0. 5 m down to 10 m. The detailed evaluation of the combined data at a few selected sites in the project area yielded precise and satisfying results. The comparison of the depth deviation between the hydromapping and sonar data is generally less than 10 cm at depths down to 5 m. The sources of error between these two technologies are further described within the paper and set out a maybe new future in capturing and handling shallow water datasets and the highly promising approach of data merging. Furthermore, a variety of new opportunities for further analysis can be achieved if such data are combined with high-resolution aerial (approximately less than 5 cm/pixel) or spectral images. The combination of these datasets including topography, bathymetry, aerial and spectral pictures provide a comprehensive and homogeneous data basis for a detailed and precise description of river- or coastal-bed hydraulic, morphologic and ecohydraulic processes. The high density and accuracy of information offer the extended possibility for monitoring and supervisory aspects.
Year: 2013