Accuracy and efficiency of the Laser-camera

A new measuring device - the Laser-camera - was tested under typical forest conditions. With the device, constructed of a Canon EOS 400D digital reflex camera with an integrated Mitsubishi ML101J27 laser line generator, diameters of trees can be measured from the centre of a sample plot without having to visit the trees. The Laser-camera's principle is based on the reflection of a laser line and a point on a tree stem and the processing of digital images. The study material was gathered during the period in 2007-2008 from 13 circular sample plots and included a total of 728 diameter measurements from 265 trees. The standard error of the diameter observations, using semiautomatic interpretation, was 6 mm (5.3%). The accuracy of the diameter observations (standard error) was maximum for spruce (5.0 mm, 4.4%, followed by birch (6.4 mm, 3.3%) and pine (7.6 mm, 7.6 %). The most common errors were caused by the laser point not hitting the tree stem, branches in front of the stem hampering visibility or incorrect definition of the direction and height of the measurement. Overall tree diameter measurements can be obtained with a Laser-camera rapidly (10 s/tree) and with good reliability and efficiency. The future goal will be to integrate laser technique with an altimeter, data collection unit and GPS receiver inside a weatherproof Laser-camera device. This will enable ready checking of the measurement results in the field from the screen of the digital camera and the measuring of the diameters at any height of a tree, the heights, locations, as well as quality variables of trees.