Mapping shallow inland running waters with UAV-borne photo and laser bathymetry : The Pielach River showcase

Abstract

Mapping and monitoring of inland water bodies is of high scientific, economic and ecological importance. Depending on the size, depth and turbidity of the river, either acoustic or optical methods are suited for the acquisition of dense and accurate 3D bathymetry data. For relatively small, clear and shallow alpine rivers, optical methods are the first choice. Either images or laser scans are taken from crewed or uncrewed platforms to map the river bottom. For more than a decade, a near natural reach of the pre-alpine Pielach River in eastern Austria has been repeatedly surveyed with laser and photo bathymetry. In this contribution, we present an open benchmark dataset (DOI: 10.48436/taz19-r6618), which was captured in October 2024 following a devastating flood event in September 2024 with multicopter drones. We present the measurement campaign including airborne and terrestrial surveys and the data processing steps. Next to standard processing, we introduce new and innovative image-based bathymetry techniques for rivers with dynamic, wavy water surfaces. We show that image sequences can be used to mitigate the water surface dynamics; synchronous oblique drone images can be used to reconstruct the undulating water surface; and Neural Radiance Fields are an alternative option to classical methods for mapping bathymetry.