Multiscale Very-High Resolution Topographic Models in Alpine Ecology: Pros and Cons of Airborne LiDAR and Drone-Based Stereo-Photogrammetry Technologies

Abstract

The vulnerability of alpine environments to climate change presses an urgent need to accurately model and understand these ecosystems. Popularity in use of digital elevation models (DEMs) to derive proxy environmental variables has increased over the past decade, particularly as DEMs are relatively cheaply acquired at very high resolutions (VHR; <1m spatial resolution). Here, we implement a multiscale framework and compare DEM-derived variables produced by Light Detection and Ranging (LiDAR) and stereo-photogrammetry (PHOTO) methods, with the aims of assessing their relevance and utility in species distribution modelling (SDM). Using a case study on the arctic-alpine plant Arabis alpina in two valleys in the western Swiss Alps, we show that both LiDAR and PHOTO technologies can be relevant for producing DEM-derived variables for use in SDMs. We demonstrate that PHOTO DEMs rivalled the accuracy of LiDAR, putting the current paradigm of LiDAR being the more accurate of the two methods into question. We obtained DEMs at spatial resolutions of 6.25cm-8m for PHOTO and 50cm-32m for LiDAR, where we determined that the optimal spatial resolutions of DEM-derived variables in SDM were between 1 and 32m, depending on the variable and site characteristics. We found that the reduced extent of PHOTO DEMs altered the calculations of all derived variables, which had particular consequences on their relevance at the site with heterogenous terrain. However, for the homogenous site, we found that SDMs based on PHOTO-derived variables generally had higher predictive powers than those derived from LiDAR at matching resolutions. From our results, we recommend carefully considering the required DEM extent to produce relevant derived variables. We also advocate implementing a multiscale framework to appropriately assess the ecological relevance of derived variables, where we caution against the use of VHR-DEMs finer than 50cm in such studies.

Positional errors in species distribution modelling are not overcome by the coarser grains of analysis

“…We intentionally developed our models with fine‐scale environmental data that are increasingly adopted for SDMs (e.g. de Vries et al, 2021; Guillaume et al, 2021; Mitchell et al, 2017). Although so far, such data are typically used in models developed to assess species–environment relationships at a landscape scale, it has been highlighted that they can be crucial for understanding species distributions at global scales (Lembrechts, Lenoir, et al, 2019; Lembrechts, Nijs, & Lenoir, 2019; Stark & Fridley, 2022; Zellweger et al, 2019).…”

Development of a river DTM generation algorithm based on SfM point clouds using vegetation and morphological filters

“…Despite applying morphological filters in SfM methods, misclassifications of roof-like terrains, such as tree canopies or shrubs, can still occur [35]. Additionally, various factors, including low color contrast and morphological similarity between points in water or dense vegetation, or real-time variations in reflected light or environmental conditions, can lead to the generation of fake points [46,[63][64][65][66]. While vegetation filters utilizing color information can partially remove these fake points, morphological filters can effectively eliminate vegetation points that were misclassified as ground points by vegetation filters.…”

Comparison Assessment of Digital 3d Models Obtained by Drone-Based Lidar and Drone Imagery

“…Lin et al (2019) evaluated the relative performance of UAV LiDAR in mapping coastal environment when compared to the UAV photogrammetry. Guillaume et al (2021) in a study for Alpine ecology implemented a multiscale framework and compare 3D models variables produced by UAV-LiDAR and stereo-photogrammetry methods, with the aim of assessing their relevance and utility in species distribution modelling. In the following of this article, we will present a study carried out in Morocco for the evaluation of the 3D products derived from a mission by LIDAR in comparison with those of a mission by drone imagery.…”