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Doctoral thesis2017Open access

Data collection for forest management planning using stereo photogrammetry

Bohlin, Jonas

Abstract

Forest managers need information about the forest state for planning treatments. The information needs to be sufficient for the purpose and preferably obtained at low cost and with regular updates. In the last decade, development and use of airborne laser scanning (ALS) for forest variable estimation has been a revolution for forest management planning. But it has also created opportunities for other three dimensional (3D) technologies which can describe the forest canopy surface, since it provides an accurate model of the ground elevation. One such technique is stereo photogrammetry using aerial images. Using aerial images from national image surveying programs, high resolution 3D data and spectral data can be acquired regularly with a frequency of about 2-4 years over forest land in Sweden. The aim was to produce forest variable raster maps which can be used at stand level but also as information to describe within stand variation and updating stand boarders after clear-cut. In this thesis aerial images from the National Land Survey’s image acquisition program has been used in all studies, but also high resolution and highly overlapping images have been evaluated. Using field plots, the 3D and spectral data can be linked by models to predict forest variables of interest. In this thesis; tree height, diameter, basal area, stem volume, species-specific stem volume and species proportions have been the variables of interest. Models have been applied and evaluated at Remningstorp in southern Sweden (Lat. 58°N, Long. 13°E), but also scaled up to national level using field plots from the national forest inventory. The included studies show that aerial images can produce forest variable estimates with good accuracy where best results in terms of root mean square error of the mean were 8.8% for tree height, 14.9% for basal area and 13.1% for stem volume, but that species-specific variables did not perform as well. In conclusion, aerial images with 0.5 m resolution and 60% overlap using stereo photogrammetry produce estimates with an acceptable level of accuracy for use as a data source for forest management planning. However, very sparse forests, deciduous forests and mature forests have larger estimation errors. Nevertheless, from a forest management perspective, forest information can be collected at very low costs and with high spatial and temporal resolution.

Keywords

area-based approach, aerial images, image matching, multi-spectral lidar, forest management planning, forest variables, photogrammetry, remote sensing, species-specific

Published in

Acta Universitatis Agriculturae Sueciae
2017, number: 2017:109ISBN: 978-91-7760-108-1, eISBN: 978-91-7760-109-8Publisher: Department of Forest Resource Management, Swedish University of Agricultural Sciences.