A Long-Term Terrestrial Laser Scanning Measurement Station to Continuously Monitor Structural and Phenological Dynamics of Boreal Forest Canopy

Abstract

The terrestrial laser scanner (TLS) has become standard technology for vegetation dynamics monitoring. TLS time series have significant underlying application in investigating structural development and dynamics on a daily and seasonal scale. However, the high potential of TLS for the monitoring of long-term temporal phenomena in fully grown trees with high spatial and temporal resolution has not yet been fully explored. Automated TLS platforms for long-term data collection and monitoring of forest dynamics are rare; and long-term TLS time series data is not yet readily available to potential end-user, such as forestry researchers and plant biologists. This work presents an automated and permanent TLS measurement station that collects high frequency and high spatial resolution TLS time series, aiming to monitor short- and long-term phenological changes at a boreal forestry field station (0.006° angular resolution, one scan per hour). The measurement station is the first of its kind considering the scope, accuracy, and length of the time series it produces. The TLS measurement station provides a unique dataset to monitor the 3D physical structure of a boreal forest, enabling new insights into forest dynamics. For instance, the information collected by the TLS station can be used to accurately detect structural changes in tree crowns surrounding the station. These changes and their timing can be linked with the phenological state of plants, such as the start of leaf-out during spring growing season. As the first results of this novel station, we present time series data products collected with the station and what detailed information it provides about the phenological changes in the test site during the leaf sprout in spring.

Automated and Permanent Long-Range Terrestrial Laser Scanning in a High Mountain Environment: Setup and First Results

“…Other examples of automated and/or permanent TLSs include near-real-time change detection of the Séchilienne landslide in France (Kromer et al, 2017), a snow study site in the eastern Sierra Nevada to review TLS positional accuracies (Hartzell et al, 2015), a site in Finland to monitor structural and phenological dynamics of boreal forest canopy (Campos et al, 2021) and a study area in the Western Austrian Alps to monitor potential avalanche slopes in high-alpine terrain (Adams et al, 2014). The limitations of these studies are that the scanners were installed for shorter periods of time (weeks to seasons) at shorter ranges (Kromer et al, 2017;Campos et al, 2021;Adams et al, 2014) or a scanner operating at a wavelength unsuitable for snow and ice was used (Hartzell et al, 2015).…”

Terrestrial laser scanning: a new standard of forest measuring and modelling?

“…Thus, it is safe to say that applying terrestrial laser scanning (TLS) to forests was certainly a game changer. The surface of a tree can be sampled over a million times within minutes to capture its full 3D structure ( Liang et al , 2016 ), even at sub-centimetre-level spatial resolution ( Campos et al , 2020 ). Furthermore, the scans contain information about the forest bed and surrounding trees and the understorey as well ( Calders et al , 2020 ).…”

“…Openly available stand structure scanned by TLS may well become a similar but far more informative standard of forest characterization as are the conventional reports of manually measured tree density, height and stem diameter. The benefit for both forest inventories and forest research is that there will no longer be a limited set of individual measurements of individual sample trees, but rather a comprehensive 3D model – or a time series of 3D models – storing the development of all trees within an entire forest stand and providing data to access countless tree and stand properties applicable to many research questions ( Campos et al , 2020 ).…”

Influence of Spatial and Temporal Resolution on Time Series-Based Coastal Surface Change Analysis Using Hourly Terrestrial Laser Scans

“…Automatic terrestrial laser scanning (TLS) from a fixed location enables to generate 3D time series of a topographic scene at high spatial and temporal resolution over long periods (e.g. Campos et al, 2021;O'Dea et al, 2019;Williams et al, 2018). One important reason for high-frequency acquisition is that induced surface alterations may be temporary, and hence missed or misinterpreted when using larger observation intervals (Anders et al, 2019).…”

“…This applies particularly in settings where processes do not occur in a dominant and uniform direction, as with gravitational mass movements of a landslide or rockfalls (e.g., Kromer et al, 2017;Williams et al, 2018). An illustrative example of highly complex change dynamics is vegetation monitoring, where the movement of leaves and branches through wind or periodic circadian movement of trees can be captured by high-frequency TLS (Campos et al, 2021;Zlinsky et al, 2017). For the example of coastal monitoring, the observation of a sandy beach by permanent TLS enables to capture dynamic sediment transport through wind, waves, and anthropogenic modifications at centimetre scales over time spans of few hours to weeks up to seasonal or annual periods (O'Dea et al, 2019;Vos et al, 2017).…”