The datasets used during the current study are available from the corresponding author on reasonable request. PLoS One 10 11 :e Remote Sens Environ — Article Google Scholar. Ecol Indic — Climate 6 1 Bu G, Wang P Adaptive circle-ellipse fitting method for estimating tree diameter based on single terrestrial laser scanning.
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You can also search for this author in PubMed Google Scholar. YX and JZ identically cooperated in the experiments, processed the data, analyzed the results and wrote the majority of the manuscript. ZS and HZ formulated the research framework, designed the experiment and methodology. ZS participated the manuscript writing, reviewed and edited the earlier version. SP guided the equipments using and participated in data processing.
XC participated in data collection. All authors read and approved the final manuscript. Correspondence to Zehao Shen. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.
Reprints and Permissions. Xie, Y. Accuracy assessment and error analysis for diameter at breast height measurement of trees obtained using a novel backpack LiDAR system.
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Table 1: Descriptive statistics of diameter at breast height DBH measured by diameter tapes. Table 2: Descriptive statistics of DBH measured by caliper. Table 3: Descriptive statistics of tree height measured with Laser range finder. The diameter tapes and calipers for measuring DBH and the laser rangefinder for measuring tree height are implemented with conventional operations. The device adopted in this paper to measure DBH and tree height uses the following steps. The surveyor records the DBH.
If the trunk of the tree is irregular, the surveyor may need to change the contact position and take multiple measurements; finally, the average value can be automatically calculated. An example of a physical image of DBH measurement is shown in Figure 7-a. The surveyor stands away from the tree at a distance close to the whole tree to record the tree height. A physical image of tree height measurement is shown in Figure 7-b. After completing measurement of the DBH and tree height of each tree in turn at the target location, the DBH data and tree height can be uploaded to a PC application for statistical analysis.
Figure 7: Pictures of field measurements. Figure 8: Overview of main mechanical structures. As shown in Figure 8, the maximum length of the control box is 14 cm, and the maximum width is 8. The horizontal distances between the front face center of the laser ranging sensor and the two rotation centers are the same at 4.
The distances between the rotation centers and the arc top of the folding ruler arms are Note that the values of W, Z, and L are fixed mechanical structural values. Figure 9: Measurement principle at different DBH sizes. As shown in Figure 9, A, B and C are the points of contact between the device and the tree surface, which results in two arcs. Assume that the measured DBH is d. The DBH can be calculated by the following formula 3 :. Figure Measuring principles of tree height measurement.
The tree height measurement relies on the laser ranging sensor and dip sensor to measure the distance and angle, respectively. When measuring, it is necessary to ensure that the whole tree is not blocked within the line of sight of the surveyor. Note that the LH horizontal distance from the measurement process is not required, it is not calculated. Assume that the measured tree height is h. To realize the fast and accurate calculation of tree height, use Taylor's expansion in the following formulas:.
In terms of the special structural design of the device, as shown in Figure 11, the maximum DBH to be measured by the device is limited. Figure Display of measurement angle limit.
The tree height measurement range also requires simulation. After repetitive experiments, when the horizontal distance from the tree is between 8 and 15 m Figure 10, L H , the surveyor can obtain a better line of sight. Here, 10 m of the horizontal distance was used to carry out the simulation research. The DBH data measured by diameter tapes or calipers and the tree height data measured by the laser rangefinder were used as reference values.
The accuracy of the DBH and tree height measurements were evaluated by utilizing the bias following formulas 6 , 7 and 8 and precision following formula 9. With the measurement situation shown in Figures c and d and Table 6, the maximum tree height was The results showed that the measured data were similar to the reference data Figures Compared with diameter tape data, the device had results with a mean bias of Figures 13 showed that when the DBH sizes increased, more variation in error was observed.
The measured values were smaller than the reference values, indicating that our device underestimated the DBH compared to diameter tape Bias in Table 7. For the caliper data, our measured values were larger than the reference values, indicating that our device overestimated the DBH Bias in Table 8. Table 7: Accuracy of the DBH measurements compared with diameter tapes in different tree species.
Table 8: Accuracy of the DBH measurements compared with calipers in different tree species. Because surveyors might not be able to fully aim at the bottom and top of the tree during the measurement, tree height would be overestimated or underestimated, but the results showed that there was still a good correlation between the measured data and reference data Figure Table 9: Accuracy of the tree height measurements in different tree species.
Figure Scatter plot of measured tree height values. To evaluate the efficiency of measurement, the times including data recording and digitizing required for traditional and device measurements were recorded.
As shown in Table 10, using the device for measurements increased the efficiency by approximately 3 times. Table Comparison of work efficiency of selected measuring methods. New devices and new methods to measure DBH and tree height have been developed in recent years.
But, these devices could not measure both the DBH and tree height and needed to record data manually, and their cost were expensive.
In addition, Fan et al. Fan et al. Mikita et al. Huang et al. Although the above devices and methods had high precision, they were not suitable for conducting forest surveys based on UAVs or total stations, considering convenience. In this study, we report a novel device based on sensor and electronic technologies. Before the field experiments, we designed a simulation experiment to verify that the maximum measurable DBH and tree height could reach In the field experiment, compared with the diameter tape data, the DBH measurements had a mean bias of There were variances in different tree species Figures a and b , and more variances were observed with the diameter tape data.
Variability was attributed to multiple factors, but we speculated that the main factor was that the cross section of the tree was similar to an ellipse or superellipse. Nonetheless, the mean bias and RMSE were similar compared with conventional tools with different tree species Tables 7 and 8 , suggesting that the device and the calculation algorithm were accurate for DBH measurement. Although the results showed that the measured values were larger than the reference values, the tree height measured with the device still had good accuracy Figure Even though our measurement method was based on the trigonometric function proposed by the mechanical structure, it was simple and effective and enriched the pool of tools for the ground measurements in forest surveys.
Moreover, it was easy to carry and operate, data were automatically recorded and processed and the efficiency of measurement could be increased by approximately 3 times.
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