Assessment of manual and automated methods for updating stand-level forest inventories based on aerial photography

Abstract

Anttila, P. 2005. Assessment of manual and automated methods for updating stand-level forest inventories based on aerial photography. Dissertationes Forestales 9. 42 p. Data collection for forest planning in private forestry in Finland is based on periodic, labour-intensive, stand level field inventories. Therefore, to increase guidance for forest owners more cost-efficient methods that replace or supplement field inventories are needed so as to reallocate labour resources. In addition, for active forest owners, up-to-date information is of interest. The aim of this thesis was to test the applicability of different inventory and updating methods that are based on aerial photography for the regional forest inventory of private forests in Finland. Four approaches were chosen: 1) stand level visual interpretation of changes and simulation of stand development, 2) automatic, stand level interpretation of aerial photographs utilising nonparametric estimation, 3) automatic, photogrammetric estimation of mean height, and 4) automatic, monoscopic identification of individual trees. Approaches 1 and 2 are inventory or updating methods, while approaches 3 and 4 can be considered as components of such methods. Approach 1 was found to be appropriate for operative use for estates that have not ordered a forest plan, provided that the strict prerequisites for the inventory area are met. The accuracy of approach 2, as such, was not considered to be high enough for forest planning, but this very inexpensive method could turn out to be applicable, if its accuracy could be improved. Approach 3 was based on image matching and would be most useful as a part of other methods, like template matching in multiple images. Although only identification of trees was tested in approach 4, the applicability of whole single tree based inventory method was appraised. Relatively high costs and low accuracy limit the possibilities to use this method, in practice.