Abstract
This study explores the feasibility of applying single-scan airborne, static terrestrial and mobile laser scanning for improving the accuracy of tree height growth measurement. Specifically, compared to the traditional works on forest growth inventory with airborne laser scanning, two issues are regarded: “Can the new technique characterize the height growth for each individual tree?” and “Can this technique refine the minimum growth-discernable temporal interval further?” To solve these two puzzles, the sampling principles of the three laser scanning modes were first examined, and their error sources against the task of tree-top capturing were also analyzed. Next, the three-year growths of 58 Nordic maple trees (Crimson King) for test were intermittently surveyed with one type of laser scanning each time and then analyzed by statistics. The evaluations show that the height growth of each individual tree still cannot be reliably characterized even by single-scan terrestrial laser scanning, and statistical analysis is necessary in this scenario. After Gaussian regression, it is found that the minimum temporal interval with distinguishable tree height growths can be refined into one month based on terrestrial laser scanning, far better than the two years deduced in the previous works based on airborne laser scanning. The associated mean growth was detected to be about 0.12 m. Moreover, the parameter of tree height generally under-estimated by airborne and even mobile laser scanning can be relatively revised by means of introducing static terrestrial laser scanning data. Overall, the effectiveness of the proposed technique is primarily validated.
Highlights
The knowledge of tree height growths is increasingly required in a variety of domains, which range from forest harvest prediction for land-use planning [1] to forest dynamics characterization for climate anomaly response [2]
After Gaussian regression, it is found that the average height growth (Gm) is 0.32 m, the standard deviation of height growth (Gstd) is 0.40 m, and the mean height pertaining to the surveying day of 7 May 2009 (Hm (RoT-48)) is 6.97 m
The later phase corresponds to the Riegl-based MLS (RiM) survey, and the initial phase refers to the Roamer-based TLS (RoT) survey
Summary
The knowledge of tree height growths is increasingly required in a variety of domains, which range from forest harvest prediction for land-use planning [1] to forest dynamics characterization for climate anomaly response [2]. The traditional photogrammetric methods have already been used for long-term forest height growth surveys Their common strategy is to reconstruct the associated canopy surface models from the stereo-pairs of aerial images, and the height differences between such two models relative to different time, e.g., 32 years apart [3] or even 58 years apart [4], are deemed as the height growths of the forests of interest. This theme applicable for tree height growth measurement is briefly valid for very flat lands or open forests. As suggested by Vanclay [5], new measurement techniques need to be explored for effective tree height growth monitoring
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