A Simplified End-User Approach to Lidar Very Shallow Water Bathymetric Correction

Airborne lidar bathymetry has been evolving in recent years, and the introduction of multispectral (MS) lidar, such as the Titan sensor from Teledyne Optech, Toronto, ON, Canada, allows for comprehensive mapping of aquatic and riparian areas. However, to derive useful riverbed geomorphology data, bathymetric correction should be applied to raw data based on the proximity of individual points within the laser point cloud to the overlying water surface. Current algorithms within off-the-shelf (OTS) software were developed for flat coastal waters and lakes and, therefore, may have difficulty with shallow river channels possessing discernible surface water gradients and/or complex riparian environments. A proposed simplified correction algorithm is based on a shift (scaling with k = 0.76) in depth values. Riverbed returns are normalized toward the overlying water surface, disregarding laser beam angle of incidence for each point. The resultant simplified bathymetric correction is, therefore, available to most end users and does not rely on black box OTS solutions. Validation of the method with an MS lidar data set is presented, and the expected neglectable introduced bias (sd = 1.4 cm) for very shallow (<2 m) water is confirmed.