Estimation of forest stem volume using multispectral optical satellite and tree height data in combination

Abstract

The accuracy of forest stem volume estimation at stand level was investigated using multispectral optical satellite and tree height data in combination. The stem volumes for the investigated coniferous stands, located in southern Sweden, were in the range of 15–585 m³ ha⁻¹ with an average stem volume of 266 m³ ha⁻¹. The results from regression analysis showed a substantial improvement for the combined stem volume estimates compared with using satellite data only. The accuracy in terms of root mean square error (RMSE) was calculated to 11.2% of the average stem volume using SPOT-4 data and tree height data in combination compared with 23.9% using SPOT-4 data only. By replacing SPOT-4 data with Landsat TM data the RMSE was improved from 25.2% to 12.2%. In addition, a sensitivity analysis was performed on the combined stem volume estimates by adding random errors, normally distributed with zero expectations, with standard deviations of 1, 1.5 and 2 m to tree height data. The results showed that the RMSE increased with increasing random tree height error to 15.4%, 18.0% and 19.9% using SPOT-4 data and 16.3%, 19.2% and 21.2% using Landsat TM data. The results imply that multispectral optical satellite data in combination with accurate tree height data could be used for standwise stem volume estimation in forestry applications.

Keywords:

• Combined estimation
• forest inventory
• Landsat TM
• SPOT-4
• stand level

The authors are grateful to Associate Professor Sören Holm, Swedish University of Agricultural Sciences (SLU), Umeå, Sweden, for great help concerning the statistical analysis and for fruitful discussions. Professor Håkan Olsson and Olle Hagner, at SLU, Umeå, are acknowledged for fruitful discussions concerning the optical analysis, and Dr Gary Smith, Chalmers University of Technology, Göteborg, Sweden, for revision of the language. We would also like to thank Olle Ahlberg, Mats Ahlberg and Geir Eriksen (Forestry Society's Estate Management Company) and Anders Persson (Swedish National Board of Forestry) for valuable assistance with field and satellite data. This work was financially supported by the Swedish National Space Board and Hildur and Sven Wingquist's Foundation for Forest Research. The authors would finally like to thank the reviewers for their comments.