MISTRA DIGITAL FOREST ANNUAL REPORT 2020 1
FOREST REMOTE SENSING The image shows Langning Hu
o's work which involves removing the top layer of trees, to identify the lower layer of vegetation. EVA LINDBERG THE HOLY GRAIL OF FOREST VARIABLES IS ABOUT TO BE DISCOVERED – thanks to multispectral laser scanning LANGNING HUO Multispectral laser scanning, scanning with laser light in two or more wavelengths, opens up new possibilities for mapping large areas of forest with an elevated level of detail. This includes developing maps of tree species, which can facilitate the evaluation of biodiversity, and prove useful in forestry planning. This is something that Eva Lindberg and her research group at SLU (Swedish University of Agricultural Sciences) are working on within Mistra Digital Forest. 0 0,5 1 Kilometers (km) – Laser data has been used for more than 20 years to produce estimates of forest variables, such as volume, mean height and stem density. There are already maps with this information, for the whole country. However, what is missing are good tree species maps and also growth maps, says Eva Lindberg, senior lecturer at SLU. Multispectral laser scanning, which was the type of scanning carried out within the programme in the summer of 2019, generates 3D point clouds in several wavelengths. – In this way, we can take advantage of colour differences between the tree species, without the signal being disturbed by the colour of the ground, or by shadows, Eva Lindberg explains. New method for the production of tree species maps Decidous Pine Spruce In Mistra Digital Forest, a new method has been developed for producing maps that show tree species. Eva Lindberg has supervised Marian Schimka, a master's student from Germany, who has worked with a method based on dividing an area into small squares, raster cells. The mean value of the light intensity is calculated within that area. – In our method, each square covers a small surface unit of 50 by 50 centimeters and the result in each square is a tree species, Eva Lindberg explains and continues: – The satellite images currently being used for forest mapping have significantly larger pixels, often 10 by 10 meters, which frequently have several tree species in one and the same area. Now, using multispectral laser scanning, it is possible to produce accurate tree species maps. The Holy Grail of variables Sveaskog has acted as the supervisor, has contributed a study area, and has financed some of the high-resolution scanning in one study area that constitutes a central element in this tree species work. When asked why Sveaskog chose to participate, technology specialist Johan Ekenstedt replies that it is of great importance for forest owners to have good tree species data. 8