Development of a comprehensive model for concurrent water surface and bottom reconstruction in photo bathymetry (PhotoBathyWave)

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In photo bathymetry, photogrammetric techniques are used for 3D measurements of water bottom topography from terrestrial and aerial images taken through water surfaces. Geometric modelling in environments with different optical media must consider image ray refraction according to Snell’s Law. This requires the existence of a precise geometric model of the interface separating the optical media. If images are taken through a free-flowing water surface, the presence of waves severely impedes geometric modelling. So far, only approximate solutions exist for this task. The objective of the proposed project is to develop a generic and versatile approach for multimedia photogrammetry through open dynamic wave-affected water surfaces. Our goal is to simultaneously determine both the shape of the water surface and the submerged water bottom topography from multi-view images in an integrated photogrammetric parameter estimation procedure. This necessitates spatio-temporal modelling of an instationary water surface exploiting its refractive or reflective property as a basis for strict consideration of refraction on the optical paths in multi-ray spatial intersection for precise unbiased water bottom coordinate determination. Special emphasis will be laid on parameter determinability in order to avoid over-parametrization, which includes appropriate stochastic modelling and planning of the measurement configuration. In general, this will be addressed in an integrated approach for simultaneously determining image orientations and water surface and bottom point coordinates within an extended bundle block adjustment or in a decoupled processing framework.While a broad body of literature exists for modelling either water surface or bottom geometry with image based techniques, our aim is to estimate both from the same stereo images. The consideration of complex, dynamic wave effected water surfaces in photo bathymetry processing pipelines constitutes an innovative approach, which has the potential (i) to substantially raise the accuracy level by one order of magnitude and to (ii) considerably extend the application fields of photo bathymetry. Application fields benefiting from the research outcomes include hydroecology and hydromorphology, airborne mapping of coastal zones, UAV-based mapping of shallow inland water bodies, coral reef change detection, or manifold measurement tasks in hydromechanical laboratory channel facilities.