Objective  A scalable altimeter was developed to solve the limited landing range of measuring tree height based on trigonometric function and to realize accuracy measurement of vertical and inclined growth tree height.

  Method  Based on the principle of draw-wire sensor measuring tree height, the scalable altimeter was developed, of which main structure contained optical electricity encoder, brushless DC motor, coil and rope. The tree height measured by linen tape was taken as true value. A total of 20 vertical growth trees and 11 inclined growth trees were measured by scalable altimeter, Blume-Leiss altimeter and forest compass to compare the measurement precision, variance and t result, respectively. We measured the height of sample wood No. 8 (vertically growing sample wood) and sample wood No. 26 (obliquely growing sample wood) six consecutive times using four instruments, and compared the precision of height measurement by various instruments.

  Result  The accuracy of the scalable altimeter in measuring the height of vertically growing trees and obliquely growing trees was 0.034 and 0.028 m, respectively, with variances of 5.60 and 9.94, and precision of 0.028 and 0.015 m, respectively. The accuracy of measuring the height of vertically growing trees and obliquely growing trees using the Blume-Leiss altimeter was 0.154 and 0.267 m, respectively, with variances of 5.76 and 10.00, and precision of 0.150 and 0.125 m, respectively. The accuracy of measuring the height of vertically growing trees and obliquely growing trees with a forest compass was 0.059 and 0.183 m, respectively, with variances of 5.66 and 10.02, and precision of 0.056 and 0.066 m, respectively.

  Conclusion  The measurement accuracy results of scalable altimeter are superior to those of Blume-Leiss altimeter and forest compass. It not only solves the problem of disconnection between field surveys and indoor input, but also effectively meets the requirements of national forest resource continuous inventory and forest resource planning and design surveys for measuring the height of opposing trees.