Towards the Estimation of Tree Biomass Changes in the Sparse Subarctic Forests Using Stereo WorldView 3 Images and Historical Aerial Photographs

摘要

Subarctic forests are open woodlands sparsely populated by small trees having narrow crowns. They cover, in Canada alone, an area of more than 2.5 million km~2. Spread between the 50th and 70th northern parallels, these forests fall within the regions that are experiencing some of the greatest climate change that will likely induce variations in forest biomass. These changes could go undocumented due to the high costs of data acquisition in such remote areas of Canada. Airborne surveys (photo or lidar) are logistically difficult, and conventional remote sensing based on 2D satellite images (e.g., Landsat) lacks accuracy. Our goals are therefore to use new very high resolution satellite stereo images (31 cm pixels) to reconstruct 3D models of subarctic forests, and use historical stereo aerial photos acquired since the 1950s to create similar 3D models representing the structure of these forests in the past. In this study, we have reconstructed a digital terrain model (DTM) using stereo measurements on WorldView 3 images of sparsely wooded areas. We then performed similar stereo measurements on the top of trees and calculated their height by subtracting DTM elevations. These height measurements were in good agreement with reference data, and can afterward be used to estimate tree biomass. Similar measurements will be performed on historical aerial photographs, and the tree biomass changes, as a function of tree height and number of trees, will be estimated.