Speaker
Description
Swedish forestry has used remote sensing (RS) data for decades to support and optimize their management. Satellite images were used for manually observing forest extents or support planning of field visits. The introduction of airborne laser scanning (ALS) data has revolutionized the information content by providing 3D data much appreciated by the industry. In addition to local ALS acquisitions financed by forest companies, the Swedish National Land Survey (Lantmäteriet) has been mapping Sweden with ALS between 2009 and 2016, to collect a complete coverage that the Swedish Forest Agency with support of the Swedish University of Agricultural Sciences (SLU) has used to generate national maps of several forest variables, including biomass, stem volume, tree height and basal area. Inventory plots from the Swedish National Forest Inventory (NFI) were used to link the RS data to the interesting variables, and the resulting maps have been made freely available. The entire Swedish forest sector has quickly adapted to this new situation and field visits are already much sparser and the ones carried out are more of the manner “ensuring the RS estimations look reasonable”. The RMSE for biomass is of the magnitude 20-22% at the stand level, and the industry is quite satisfied but is also aiming for improved accuracy. They have also realized the rapid outdating of the ALS based maps, and it has been agreed on a national program that continuously will provide updated free ALS data on a 7 year repeat period. However, changes happening in-between these acquisitions, e.g., natural disasters and other changes, remain unidentified.
In 2017, we published a corresponding national map of biomass, generated on a similar manner as the ALS ones, but based on TanDEM-X data. The accuracy was about 21-25% at the stand level, and would hence probably comprise a sufficient substitute for the time in-between maps from ALS are available. It is, nevertheless, not the only possible substitute, and for example the national aerial photography mapping program also provides national data with a 2-5 year cycle. Hence, in order to provide additional value, satellite radar based solutions can (currently) mainly compete with its superior temporal coverage. Moreover, radar based products that can provide sufficient accuracy are using interferometry as processing technique and require a bi-static configuration with suitable baselines for the interferometer. Also, the influence of weather conditions can be severe, and must be further researched in order to possibly establish a near real-time forest monitoring system. Hence, the high requirements might limit the actual future use of this solution, if no synergistic advantages can be found with other applications.
In this presentation we discuss some results from ALS and TanDEM-X radar data sources in relation to expressed requirements from the industry. Moreover, the role of C-band data (such as Sentinel-1) in a future solution is touched upon.
