Mapping simulated error due to terrain slope in airborne lidar observations

Abstract

Quantification of geo-location error in light detection and ranging (lidar) observations is typically limited to empirical assessments, commonly quantified as the fundamental vertical accuracy (FVA). Methodological recommendations indicate that validation observations used for quantifying the FVA should not be collected in sloped terrain; however, terrain slope has been shown to contribute to the lidar error budget. Therefore, users of lidar information generally do not have adequate information to characterize error in sloped conditions. This study proposes a novel geometric terrain-based error propagation algorithm for simulating error bounds of individual lidar observations in the presence of terrain slope. A steep, glacierized, alpine test site in the Canadian Rockies was used to evaluate the algorithm. Error simulations were modelled from the terrain-based error propagation algorithm as well as a pre-existing sensor hardware error propagation algorithm and validated with high-accuracy GPS observations. Simulated versus observed errors showed that terrain-based error simulations provided a reasonable ‘worst-case scenario’ simulation of potential error and were superior to hardware-only simulated errors. Results were separated into three individual flight lines, and terrain-based error simulations were greater than the observed errors in 82%, 89%, and 100% of the tested points in each respective flight line, or 90%, overall. This contrasted hardware-only error simulations, which were greater than observed errors in 32%, 42%, and 84% of tested points in each respective flight line, or 50% overall. This work provides a comprehensive understanding of the distribution of errors within lidar point clouds over complex terrain types and provides a new methodology for propagating lidar observational errors into derived products.