Scanning Plants with High Precision
igg
Uncovering Hidden Information
M.Sc. Jan Dupuis, Dipl.-Inform. Stefan Paulus
Motivation
Data Aquisition
High resolved and accurate 3D plant measuring has become more
important in terms of plant phenotyping. 3D laser scanning using
active laser triangulation has the
advantage of providing complete
3D point clouds of the plant
surface with a high spatial
resolution and accuracy. However,
scanning plants with common
laser triangulation sensors (LTS)
using a red laser (~650nm) leads
to an interaction of the emitted
laser and the plant structure
(Figure 1) resulting in a lower
accuracy or incomplete point
clouds [1].
Current developments in sensor
technology enable the use of an alternative laser wavelength
(405nm) without losing any accuracy. Furthermore, integrating the
intensity of the received signal of both laser colors into the data
processing could improve the analysis of 3D plant measurements.
Two commercial LTSs, scanControl 2700-100 (red) and
gapControl 2911-100 (blue) developed by MicroEpsilon
company were used for data acquisition. These 2D laser
scanners work according to the light section method and provide
a point-to-point distance of approx. 0.150mm with an accuracy
of about 0.015mm. Using a high precision linear guidance
system with a moving table supplements the 2D LTS with the
third dimension (Figure 2).
Figure 2: Measurement Setup: A) front view, B) side view [2]
Results
Analyzing the intensity values of all measured 3D points enables a closer look on the interaction between the emitted laser and a leaf's
surface structure. Scanning epidermal layers extracted from A. porrum pointed out that the red laser provides a much stronger surface
penetration compared to the blue one. This leads to the assumption that the blue laser is backscattered from the top of the leaf's surface
while the red laser penetrates the surface structure and interacts with the underlying surface layers (Figure 1). Therefore, it should be
possible to measure the real geometry of the leaf's surface independent of the chlorophyll content using a blue LTS and to evaluate the
physiological state of a plant by analyzing the intensity values provided by the red LTS.
Red Laser
Blue Laser
Figure 3: RGB- and intensity-images of a A. parviflora leaf
Figure 3 shows the intensity images of a bottlebrush buckeye (A. parviflora) leaf with different physiological states ranging from healthy
(green) to necrotic (brown). Using the red LTS the intensity image reflects the different states of the plant. Healthy regions with high
chlorophyll content provide a low intensity while chlorotic and necrotic regions have higher intensity values. In contrast, the intensity image
of the blue LTS is almost independent of the physiological states because the laser is backscattered with any surface penetration.
Conclusion
References
Summing up, the analysis of the intensity provides a great advantage
for plant phenotyping. In fact, it was found that the intensity of the red
LTS provides detailed information about the physiological states of
the leaf while the blue LTS enables the acquisition of the real leaf's
surface due to the much smaller penetration depth. Thus, a
combination of both sensor types would provide the real surface and
the ability to analyze the physiological state of a plant.
[1] Paulus S, Eichert Th, Goldbach H E, Kuhlmann H (2014)
Limits of Active Laser Triangulation as an Instrument for
High Precision Plant Imaging, Sensors 2014, 14(2)
S. 2489-2509
[2] Dupuis J, Kuhlmann H (2014) High-Precision Surface
Inspection: Uncertainty Evaluation within an Accuracy
Range of 15μm with Triangulation-based Laser Line
Scanners, J. Appl. Geodesy, 8 (2), S. 109–118
igg
Institut für Geodäsie und Geoinformation
Professur für Geodäsie
www.igg.uni-bonn.de
Nußallee 17
53115 Bonn
Ansprechpartner:
M.Sc. Jan Dupuis
[email protected]