Mapping River Bed Topography in Whitewater Rapids Using Bathymetric <scp>LiDAR</scp>

ABSTRACT Bathymetric LiDAR captures river topography efficiently for clear and shallow water, but for mountain rivers, whitewater rapids still pose challenges. This study proposes a novel method to enable the extraction of bottom returns specifically in turbulent whitewater sections. The method outlined uses a curve fitting approach to subtract the water column from the recorded LiDAR waveform, calculates a residual of reflected energy that is not attributed to the water column, and applies peak detection on the residual to extract previously undetected returns. For the evaluation of the points derived from the additional returns, three different rivers were surveyed with both LiDAR measurements and a total station with a reflector pole. This provides the foundation for assessing the accuracy of the new underwater terrain points. Compared to the reference data, this results in a median reduction in the distance to the reference points from 20.6 to 9.2 cm and 40.4 to 22.5 cm. Because it closes significant gaps in the data where no bottom points were detected. In conclusion, this study extends the application of full‐waveform processing for bathymetric LiDAR to whitewater rivers, which opens up the field of bathymetric LiDAR for river research in the turbulent environment of mountain rivers.