Detailed and accurate 3D data with airborne laser scanning – also underwater

Finnish Geospatial Research Institute FGI?of the?National Land Survey of Finland, has expanded the acquisition of 3D laser scanning data to cover also the shallow water areas. A new sensor with green wavelength has made this possible, and first tests with the new sensor were carried out in fall 2021 in rivers Oulankajoki, Kuusinkijoki and Pulmankijoki. Combined with sonar data from deeper sections, this allows the seamless 3D-mapping of above and underwater river topography.

Text & Images: Harri Kaartinen/FGI

Multi-wavelength data for semantic riverine 3D modelling

New bathymetric laser scanner is paired with other scanners on a common platform to obtain information in multiple wavelengths (visible and infrared). The current system operates in three wavelengths: 532, 905 and 1550 nm. Each wavelength offers different qualities including enhanced 3D geometric and radiometric properties of objects, which gives more tools for data analysis, e.g. vegetation species classification and land cover type interpretation. As laser scanners use active illumination of objects, the technique is almost fully independent of ambient light, which is a great advantage compared to passive multi-spectral imagery –?lack of light is a common issue in underwater imaging.

3D point cloud collected with one scanner/waveform, point color by incoming echo intensity. Typically used near-infrared light is absorbed by water so we do not get observations from the river channel.

On-going bathymetric research

FGI has tested various laser scanning platforms in riverine environments together with University of Turku, river Pulmankijoki serving as a living lab for system testing and time-series collection for topographic 3D data for change detection. This research is now widening to cover also underwater areas, as well as new possibilities of multi-spectral data. A new data acquisition campaign is planned for coming fall at least in rivers Oulankajoki and Tenojoki and its tributary Pulmankijoki.

3D point cloud collected with three scanners/waveforms, point color by incoming echo intensity per wavelength. With green laser we get observations also from water surface and river floor.

New possibilities in various applications

In addition to riverine area mapping, FGI has several projects studying the applicability of multi-spectral laser scanning data. Three-wavelength data is tested for tree species classification, forest health and bark beetle infestation detection, forest fire risk analysis and semantic city modeling, to name a few.