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APPLICABILITY OF “BAUMHÖHENMESSER“ APPLICATION FOR MOBILE PHONES WHEN MEASURING TREE HEIGHTS

Many instruments are constructed in order to measure tree height. With further technology development 'smartphones' are developed which offer variety of different features. One of such features is the application 'Baumhöhenmesser' designed for tree height measurement. An application 'Baumhöhenmesser' installed on mobile phone Sony Xperia L with Android OS was compared with Vertex height meter. The measurement was performed in two different surroundings: on the building in the city of Zagreb where three heights were defined and measured with Vertex, and each height was measured three times with smartphone application from three predefined distances. The second was height measurement in the beech-fir selection stand where the height of each tree was measured twice with smartphone application and Vertex. Total 76 beech and 76 fir trees were measured. Data obtained when measuring height on the building with smartphone application were about 1, 2 m (4, 6 %) lower than those measured with Vertex. Accordingly, 53% of data had less than 2 m difference from heights measured with Vertex, with maximum difference 11, 1 m. In forest stand heights obtained by application were on average 0, 43 m (1, 8%) higher than Vertex data, being 0, 53 m (2%) for fir and 0, 33 m (1, 7%) for beech trees. About 63% differences were less than 2 m for fir, and 29% for beech trees, with maximum difference 10, 2 m and 15, 1 m respectively. Using paired t-test no statistically significant difference between heights obtained by two instruments was found for fir and beech trees (p=0, 05). Deviations (in absolute value) from the reference height were smaller for lesser heights, their range increases with height, while height has no influence on their positive or negative sign. Height curves (regression models) for fir and beech were constructed based on measurement data in forest stand. Determination coefficient of model obtained by data measured with Vertex is higher than data measured with smartphone application: about 9% for fir, and almost 20% for beech trees. Height curves obtained from 'Baumhöhenmesser' data are higher than those measured with Vertex. For fir trees this difference ranges from 0, 74 m (8, 7%) in diameter class 12, 5 cm to 0, 17 m (0, 4%) in diameter class 87, 5 cm. For beech trees it is from 0, 66 m (4, 8%) in diameter class 12, 5 cm to -0, 04m (0, 1%) in diameter class 87, 5 cm. Application has not proven reliable for measurement of individual trees, while it could be acceptable for larger number of trees and height curves.

height measurement, smartphone, Baumhöhenmesser, Vertex hypsometer

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