Abstract
Abstract. This work presents a data acquisition framework and the technical details of a permanent terrestrial laser scanning (TLS) measurement station for high spatial and temporal resolution forest observation that was developed in the Finnish Geospatial Research Institute. The TLS measurement station was established to provide hyper-temporal time series of three-dimensional point cloud data for long term monitoring of a boreal forest. Time series data acquisition framework consists of regular 14-minute scans performed by a RIEGL VZ-2000i laser scanner in every 30 minutes, resulting in the collection of 48 scans per day. The entire framework includes the setting up of the laser scanner, the initialization of daily project, the scanning data acquisition over a preset time window, the storage management of the collected data at a local measurement computer, and the transfer of data from the measurement computer to network-attached storage (NAS) for further data processes. The operability of the proposed TLS measurement station was first piloted at a test area of about 32,500 m2 in Southern Finland (60°09'N, 24°32'E). A set of several long monitoring experiments were performed over the whole growing season from the beginning of April to the end of October in 2019. As preliminary results, the time series outputs have captured detailed information on the phenological changes in the test site with sub-centimetre accuracy. For instance, it was possible to visualize plant dynamics phenomena, such as the sprouting of leaves in spring and their falling in autumn.
Highlights
The high penetrability of laser beam associated with the ability to acquire multiple returns per transmitted pulse makes the laser scanning systems a unique measurement tool for data acquisition (Wehr, Lohr, 1999), three-dimensional representation and biophysical analysis of forest environments (Eitel et al, 2016)
The permanent Terrestrial laser scanning (TLS) measurement station presented in this work is developed to provide time series data for short and long-term analyses, which can provide new insights about boreal forest dynamics
Movement dynamics and seasonal changes can be detected in the TLS time series data
Summary
The high penetrability of laser beam associated with the ability to acquire multiple returns per transmitted pulse makes the laser scanning systems a unique measurement tool for data acquisition (Wehr, Lohr, 1999), three-dimensional representation and biophysical analysis of forest environments (Eitel et al, 2016). Terrestrial laser scanning (TLS) can acquire forest measurements from a close-to ground perspective and regardless the external lighting conditions, which enables the constant extraction of forest structural parameters at an individual tree level without interfering their internal processes. High temporal-density scans and short scanning interval are needed to detect tree dynamic behaviour on a daily basis. This leads to large data sets that have to be processed and stored efficiently. The information acquired in the TLS station accurately detects structural changes in tree crowns. These changes can be linked with phenological state in plants and the internal processes driving the changes. To fully utilize the information acquired with TLS-based time series, a rigorous and straightforward framework is required to detect and quantify target changes
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