Analysis and correction of ocean wave pattern induced systematic coordinate errors in airborne LiDAR bathymetry

• Published in: ISPRS journal of photogrammetry and remote sensing Vol. 128; pp. 314 - 325
• Main Authors: Westfeld, Patrick, Maas, Hans-Gerd, Richter, Katja, Weiß, Robert
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2017
• Subjects: Accuracy analysis; Airborne LiDAR bathymetry; Multimedia; Refraction; Underwater; Water surface modeling; Wave pattern; Multimedia; Airborne LiDAR bathymetry; Water surface modeling; Refraction; Wave pattern; Underwater; Accuracy analysis
• ISSN: 0924-2716; 1872-8235
• DOI: 10.1016/j.isprsjprs.2017.04.008

This contribution investigates the effects of ocean wave patterns on 3D underwater point coordinate accuracy for LiDAR bathymetry. The refraction of the finite diameter laser pulse passing the air/water interface is modeled differentially in a strict manner. Typical wave patterns and sensor configurations are simulated, and their impact on the 3D coordinates at the bottom of the water body are systematically analyzed. It can be shown that waves have a significant effect on both the planimetry and depth coordinates of underwater topography 3D point cloud coordinates, especially for modern small footprint LiDAR systems. Planimetric effects may reach several decimeters or even meters, and depth coordinate errors also reach several decimeters, even in the case of a horizontal water body bottom. The simulations show that the simplified assumption, that wave effects average out (as is made in most LiDAR bathymetry data processing tools) is not even fulfilled for large footprint systems (spreading the laser beam to a diameter of several meters at the water surface) under certain wave pattern conditions. Modern systems with smaller beam divergence are much more sensitive to wave-induced variations of the refraction conditions and will experience significant wave pattern dependent coordinate errors. The results presented here form a basis for a more strict coordinate correction, if the wave pattern can be modeled from the LiDAR bathymetry water surface reflections or from other observations. Moreover, it will be shown that the induced coordinate errors contain a non-zero bias in addition to a local wave surface dependent quasi-random part, which allows for the formulation of wave pattern dependent correction terms in order to increase the accuracy of LiDAR bathymetry by removing systematic wave pattern dependent effects.