PhotoBathyWave

Against the background of climate change, the surveying and monitoring of water bodies is becoming increasingly important. Potential fields of application include water ecology, hydrobiology, habitat modelling and hazard zone planning. Besides geophysical and hydro-acoustic methods, optical methods are employed in shallow water areas. A cost-effective method is multimedia photogrammetry, also referred to as photo bathymetry, in which 3D reconstruction is based on overlapping photos. In contrast to classical stereo photogrammetry, photo bathymetry must also take into account the beam refraction at the water surface. The water surface is particularly difficult to detect in vertical images, which is why in practice rough approximations are often used. Especially with high spatial resolution images, e.g. from acquired with drones, these simplifications cause inaccuracies in the reconstructed water depths. The aim of the PhotoBathyWave project is to develop a versatile generic model for multimedia photogrammetry for the general case of moving water surfaces. For this purpose, both the topography of the water bottom and parameters describing the water surface are determined simultaneously in an integrated photogrammetric approach. The dynamic water surface can either be modelled continuously over time or statically, separately for each image acquisition time. Both variants are to be explored in the project and tested with regard to their applicability in different recording scenarios (multi-camera system in the hydraulic engineering laboratory, aerial case, and drone photos). Another focus is on capturing the water surface itself, where reflective and refractive techniques are investigated. Reflective methods (shape from specular reflection) require the use of simultaneous image acquisition from multiple positions (e.g. by drone squadrons). In refractive methods, the displacements of image points because of beam refraction serve as observables for water surface reconstruction. Regardless of the chosen modelling approach, the goal is to describe the water surface in as much detail as possible with as few parameters as possible. More precise modelling of the water surface can increase the accuracy potential of photo bathymetry by about an order of magnitude and thus significantly expand the range of applications. This requires the integration of image orientation and the determination of water surface and water body topography in a comprehensive process (integrated bathymetric bundle block). This must also take into account aspects of (dense) image matching, which is hampered by beam refraction and scattering. In any case, parameter estimation techniques are consistently applied to analyse the determinability and significance of all unknown parameters.