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pxhere.com required information.
There are two main types of laser scanners: Airborne
Laser Scanners (ALSs), mounted on aerial vehicles, and
Terrestrial Laser Scanners (TLSs), ground-based instruments.

ALSs are less suitable for evaluating stem attributes beyond
dimensions and are primarily used for biomass and forest
structure investigations.
TLSs have been tested for evaluating stem form and
individually, while qualitative assessments define a class based branchiness, and some studies are available for stem defect
on rules providing different admissibility criteria for the several detection. Currently, both static (mounted on tripods) and
attributes to be assigned to the various classes. mobile (hand-held or worn in a backpack) TLSs are available.
Quantitative surveys are more time- and resource-intensive Further technical and operational details on TLSs are
but allow for a more accurate prediction of quality. reviewed.

On the other hand, qualitative assessment can be quicker The results indicated that visual classification was ineffective
but requires greater harmonisation efforts due to historical for distinguishing stem form and lean qualitatively, as no
differences in criteria among countries or local customs. significant differences were detected among the classes. TLSs
Several qualitative assessment procedures focus on the provided more precise results for use in stem quality grading.
first 5–6 m of the tree height due to cost considerations and Similar comparisons were conducted by Mengesha et al.
because the greatest value is often concentrated in this part for the taper, sweep, and lean of ash stems calculated from
of the stem, especially for broad-leaved trees. TLS data and manually in the field. They observed superior

Visual characteristic measurement can be manual, where results when the laser scanner survey was performed during
an operator detects the parameters of interest, but this is the leaf-off season.
expensive and, especially for some particularly burdensome In a study on Scots pine, Pyörälä et al. compared geometric
attributes (for example, branchiness), impractical for large- data (diameter, volume, taper, and sweep) obtained from
scale surveys. An alternative involves recording the quality point clouds on standing trees with the same measurements
class of each analysed tree, which is faster but leads to the taken at the sawmill at the log level using an operational
problems mentioned above and can be influenced by operator laser scanner. They found that dimensional data from stem
experience and subjectivity. and log assessments were closely correlated, but the same
Over time, promising technologies have emerged to was not true for sweep, which was difficult to predict from

automate survey work, making it faster but still detailed, standing trees.
enabling large-scale implementation. These can be categorised Numerous studies have examined the viability of assessing
as laser-based or image-based techniques. branch characteristics using laser scanner technology.
One widely used technology for qualitatively evaluating For instance, in Scots pine, the attributes of the whorls
stem characteristics is the laser scanner. Very briefly, laser (number, position, and max diameter) were extracted from a
scanners measure distances between objects in the environment TLS survey and compared with the same variables obtained
and the sensor and generate point clouds that reconstruct by X-ray analysis on cut logs.

detected objects in a highly accurate way. These point clouds Branch attributes were not directly comparable with knot
can be processed using various algorithms to extract the features derived from the logs, partly due to measurement