Canadian Forest Service Publications
Comparing ALS and Image-Based Point Cloud Metrics and Modelled Forest Inventory Attributes in a Complex Coastal Forest Environment. 2015. White, J.C., Stepper, C., Tompalski, P., Coops, N.C., Wulder. M.A. Forests. Vol. 6, 3704-3732.
Issued by: Pacific Forestry Centre
Catalog ID: 36440
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Digital aerial photogrammetry (DAP) is emerging as an alternate data source to airborne laser scanning (ALS) data for three-dimensional characterization of forest structure. In this study we compare point cloud metrics and plot-level model estimates derived from ALS data and an image-based point cloud generated using semi-global matching (SGM) for a complex, coastal forest in western Canada. Plot-level estimates of Lorey’s mean height (H), basal area (G), and gross volume (V) were modelled using an area-based approach. Metrics and model outcomes were evaluated across a series of strata defined by slope and canopy cover, as well as by image acquisition date. We found statistically significant differences between ALS and SGM metrics for all strata for five of the eight metrics we used for model development. We also found that the similarity between metrics from the two data sources generally increased with increasing canopy cover, particularly for upper canopy metrics, whereas trends across slope classes were less consistent. Model outcomes from ALS and SGM were comparable. We found the greatest difference in model outcomes was for H (ΔRMSE% = 5.04%). By comparison, ΔRMSE% was 2.33% for G and 3.63% for V. We did not discern any corresponding trends in model outcomes across slope and canopy cover strata, or associated with different image acquisition dates.
Plain Language Summary
Three-dimensional information from ALS data is transforming forest inventories. There is currently great interest in the forestry community regarding the potential of generating similar 3D information from digital airborne imagery. In our manuscript, we report the results of a detailed investigation we conducted into the relative performance of ALS and image-based point clouds in a complex, coastal forest environment in western Canada. We compare both point cloud metrics and plot-level model outcomes (Lorey's mean height, basal area, and gross volume) from these two data sources across a range of slope and canopy cover conditions, in addition to assessing the impact of image acquisition date on model outcomes. This research represents a novel contribution to the scientific literature on this topic and will be of great interest to scientists and practitioners.