Abstract
BackgroundThe LiBackpack is a recently developed backpack light detection and ranging (LiDAR) system that combines the flexibility of human walking with the nearby measurement in all directions to provide a novel and efficient approach to LiDAR remote sensing, especially useful for forest structure inventory. However, the measurement accuracy and error sources have not been systematically explored for this system.MethodIn this study, we used the LiBackpack D-50 system to measure the diameter at breast height (DBH) for a Pinus sylvestris tree population in the Saihanba National Forest Park of China, and estimated the accuracy of LiBackpack measurements of DBH based on comparisons with manually measured DBH values in the field. We determined the optimal vertical slice thickness of the point cloud sample for achieving the most stable and accurate LiBackpack measurements of DBH for this tree species, and explored the effects of different factors on the measurement error.Result1) A vertical thickness of 30 cm for the point cloud sample slice provided the highest fitting accuracy (adjusted R2 = 0.89, Root Mean Squared Error (RMSE) = 20.85 mm); 2) the point cloud density had a significant negative, logarithmic relationship with measurement error of DBH and it explained 35.1% of the measurement error; 3) the LiBackpack measurements of DBH were generally smaller than the manually measured values, and the corresponding measurement errors increased for larger trees; and 4) by considering the effect of the point cloud density correction, a transitional model can be fitted to approximate field measured DBH using LiBackpack- scanned value with satisfactory accuracy (adjusted R2 = 0.920; RMSE = 14.77 mm), and decrease the predicting error by 29.2%. Our study confirmed the reliability of the novel LiBackpack system in accurate forestry inventory, set up a useful transitional model between scanning data and the traditional manual-measured data specifically for P. sylvestris, and implied the applicable substitution of this new approach for more species, with necessary parameter calibration.
Highlights
The LiBackpack is a recently developed backpack light detection and ranging (LiDAR) system that combines the flexibility of human walking with the nearby measurement in all directions to provide a novel and efficient approach to LiDAR remote sensing, especially useful for forest structure inventory
In order to quantify the potential impacts of these factors on the uncertainty of the forest measurements obtained with this novel instrument, we investigated a Pinus sylvestris var. mongolica plantation containing trees of different ages in the Saihanba Natural Forest Park, Hebei Province in northern China, where we focused on the accuracy and uncertainty of the diameter at breast height (DBH) measurements, the most important forest structure parameter
RA values of DBHLi in different tree size classes For all of the sampled trees pooled into five diameter classes, the relative accuracy (rA) values for DBHLi varied with the slice
Summary
The LiBackpack is a recently developed backpack light detection and ranging (LiDAR) system that combines the flexibility of human walking with the nearby measurement in all directions to provide a novel and efficient approach to LiDAR remote sensing, especially useful for forest structure inventory. The traditional forestry inventory uses a ruler and rangefinder to measure structural indices such as the DBH and height stem by stem at the forest stand scale (Liu et al 2018a, 2018b), and predictive models are fitted for regional estimates of forest metrics such as the timber volume or biomass (le Maire et al 2011). This approach is always limited by the available labor force and operating time. Compared with traditional spectral remote sensing technology, LiDAR is better at extracting the three-dimensional (3D) structural characteristics of vegetation, and it is increasingly used in forestry inventory and forest ecology research (Lim et al 2003; Davies and Asner 2014; Alonzo et al 2015)
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