The doctoral dissertation in the field of Forest Sciences will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus.
What is the topic of your doctoral research? Why is it important to study the topic?
The topic of is large-scale estimation of boreal forest leaf area index (LAI) with airborne laser scanning (ALS) data in Finland. LAI is defined as half of the two-sided leaf area per unit horizontal ground surface area. It quantifies the amount of foliage present in the canopy, where the vital mass and energy exchanges occur between the biosphere and the atmosphere. Therefore, temporally and spatially accurate LAI data are of great importance for forest ecology and environmental research. Consequently, high-resolution LAI maps at national and global scales are highly desired.
Specifically, this research study investigates whether incorporating novel ALS-based metrics can improve LAI estimation, assesses the performance of different LAI modelling approaches at both regional and nationwide scales, examines the effectiveness of calibrating nationwide models using local sample plots, and proposes a gamified framework for innovative in situ LAI data collection.
What are the key findings or observations of your doctoral research?
The results highlight the feasibility of various modelling approaches and multiple discrete-return ALS datasets for large-area mapping of LAI at both regional and nationwide scales. The findings confirmed that both empirical and semi-physical modelling approaches can achieve satisfactory accuracy. While empirical models yielded slightly higher accuracy, semi-physical models offered greater robustness and transferability across varying conditions. Each modelling approach has distinct benefits and limitations, and the determination of appropriate modelling approach should be guided by the specific objectives of future projects.
What are the key research methods and materials used in your doctoral research?
This research collected field-measured digital hemispherical and cover photographs across nine study sites in Finland as reference data. It also utilised data from the nationwide airborne laser scanning campaign conducted by the National Land Survey of Finland (https://www.maanmittauslaitos.fi/en/maps-and-spatial-data/datasets-and-interfaces/product-descriptions/laser-scanning-data-5-p) to provide accurate LAI predictions at high spatial resolution. The final results of this research can be used to provide high-resolution LAI maps over large geographical areas.
The doctoral dissertation of Shaohui Zhang, MSc, entitled Large-scale estimation of boreal forest leaf area index with airborne laser scanning data be examined at the Faculty of Science, Forestry and Technology, Joensuu Campus. The opponent will be Research Professor Svein Solberg, Norwegian Institute of Bioeconomy Research (NIBIO), Norway, and the custos will be Professor Lauri Korhonen, University of Eastern Finland. Language of the public defence is English.
