In his bachelor thesis, Matthias Lemke discussed the question of whether it is possible to draw conclusions about forest stand management and, in particular, the intensity of intervention on the basis of two 3D crown models recorded at different times. Gathering data with UAV images, Matthias Lemke applied remote sensing methods to answer his research question.
Matthias Lemke analysed a 33 year old single layer Douglas-fir stand. He compared two 3D crown models of the area. Aerial imaging of the stand was conducted using a commercially available UAV. The first imagery flight on 06/20/2017 captured the stand in an unthinned condition. The second image flight took place on 03/25/2018, after completion of the thinning measure. According to the harvester protocol, between the flights 533 individual trees were removed
The aerial imagery obtained was then processed using Pix4Dmapper software to produce two 3D stand models and two digital orthophotos (DOPs), which were then compared. The DOPs were evaluated using a forest aerial photo interpretation key. Comparison of the 3D stand models for differences in canopy cover was conducted using the CloudCompare programme.
Matthias Lemke found that tree in the stand of higher Kraft’s classes removed in the course of thinning could be well localized. Lower Douglas firs with smaller or additionally constricted crowns were not or hardly visible. The HNEE graduate, therefore, recommends an increase in the detail of the stand crown structure in the 3D point cloud, but also an increase in the image sharpness in the DOP.
This can be achieved using the same UAV, for example with lower flight altitudes. Alternatively, the use of a UAV from the professional sector and appropriate camera technology can be employed. To obtain a more realistic crown roughness in the 3D stand model, oblique aerial images of the stand could also be generated in the course of UAV aerial image acquisition. This results in a more spatial representation of the stand on the individual aerial images and may have a positive effect on the subsequent representation of the stand’s crown structure in the 3D point cloud.
Content and images: Matthias Lemke