Ground-based Laser Scanning Research Articles

Estimating the plant area density of a Japanese larch ( Larix kaempferi Sarg.) plantation using a ground-based laser scanner

The three-dimensional (3D) distribution of plant area density (PAD) is difficult and time-consuming to determine. In this study, we measured this distribution using a ground-based laser scanner consisting of a laser range finder and two rotation stages, and compared the results with those obtained based on the attenuation of solar radiation and litter traps. To determine the 3D distribution of PAD, we divided the forest horizontally and vertically to define volume elements (voxels). In each voxel, we calculated PAD from the gap fraction, which was defined as the probability that laser beams from the forest floor would pass through the voxel without interception. Measurements were obtained four or five times between the in-leaf and leafless periods in 45- and 46-year-old Japanese larch ( Larix kaempferi Sarg.) plantations with different stem densities after thinning. We found the following: (1) Because the largest tree height was greater than the highest point of interception of the laser beams, our method underestimated PAD in the upper layer of the forest. (2) Compared with estimates based on the attenuation of solar radiation, our method overestimated plant area index (PAI) by around three units throughout the season, but successfully captured the reduction of PAI between bud break and leaf-fall. (3) The horizontal distribution of PAI estimated by our method was well correlated with that estimated using litter traps and reproduced the horizontal non-uniformity of PAI. Despite some limitations, such as the diameter and divergence angle of the laser beam, the ground-based laser scanner successfully provided direct, non-destructive estimates of the forest's 3D distribution of PAD.

Geometric validation of a ground-based mobile laser scanning system

This paper outlines a study, carried out on behalf of a national mapping agency, to validate laser scanned point cloud data collected by a ground-based mobile mapping system. As the need for detailed three-dimensional data about our environment continues to grow, ground-based mobile systems are likely to find an increasingly important niche in national mapping agency applications. For example, such systems potentially provide the most efficient data capture for numerical modelling and/or visualisation in support of decision making, filling a void between static terrestrial and mobile airborne laser scanning. This study sought to assess the precision and accuracy of data collected using the StreetMapper system across two test sites: a peri-urban residential housing estate with low density housing and wide streets, and a former industrial area consisting of narrow streets and tall warehouses. An estimate of system precision in both test sites was made using repeated data collection passes, indicating a measurement precision (95%) of between 0.029 m and 0.031 m had been achieved in elevation. Elevation measurement accuracy was assessed against check points collected using conventional surveying techniques at the same time as the laser scanning survey, finding RMS errors in elevation in the order of 0.03 m. Planimetric accuracy was also assessed, with results indicating an accuracy of approximately 0.10 m, although difficulties in reliably assessing planimetric accuracy were encountered. The results of this validation were compared against a theoretical error pre-analysis which was also used to show the relative components of error within the system. Finally, recommendations for future validation methodologies are outlined and possible applications of the system are briefly discussed.

From outcrop to reservoir simulation model: Workflow and procedures

Advances in data capture and computer technology have made possible the collection of three-dimensional, high-resolution, digital geological data from outcrop analogs. This paper presents new methodologies for the acquisition and utilization of three-dimensional information generated by ground-based laser scanning (lidar) of outcrops. A complete workflow is documented—from outcrop selection through data collection, processing and building of virtual outcrops—to geological interpretation and the building of geocellular models using an industry-standard, reservoir-modeling software. Data sets from the Roda Sandstone in the Spanish Pyrenees and the Grabens region of Canyon-lands National Park, Utah, USA, are used to illustrate the application of the workflow to sedimentary and structural problems at a reservoir scale. Subsurface reservoir models are limited by available geological data. Outcrop analogs from comparable systems, such as the Roda Sandstone and the Grabens, are commonly used to provide additional input to models of the subsurface. Outcrop geocellular models can be analyzed both statically and dynamically, wherein static examination involves visual inspection and the extraction of quantitative data on body geometry, and dynamic investigation involves the simulation of fluid flow through the analog model. The work presented in this study demonstrates the utility of lidar as a data collection technique for the building of more accurate outcrop-based geocellular models. The aim of this publication is to present the first documentation of a complete workflow that extends from outcrop selection to model investigation through the presentation of two worked data sets.

Ground-based Laser Imaging for Assessing Three-dimensional Forest Canopy Structure

Improved understanding of the role of forests in carbon, nutrient, and water cycling can be facilitated with improved assessments of canopy structure, better linking leaf-level processes to canopy structure and forest growth. We examined the use of high-resolution, ground-based laser imaging for the spatially explicit assessment of forest canopies. Multiple range images were obtained and aligned during both leaf-off and leaf-on conditions on a 20 m × 40 m plot. The plot location was within a mixed species broadleaved deciduous forest in western North Carolina. Digital terrain and canopy height models were created for a 0.25 m square grid. Horizontal, vertical, and three-dimensional distributions of plant area index, created using gap-fraction based estimation, had 0.5 m resolution for a cubic lattice. Individual tree measurements, including tree positions and diameter at breast height, were made from the scanner data with positions, on average, within 0.43 m and diameters within 5 cm of independent measurements, respectively. Our methods and results confirm that applications of ground-based laser scanning provide high-resolution, spatially-explicit measures of plot-level forest canopy structure.

リモートセンシングデータを利用した林分構造の計測

The increase of CO2 absorption by afforestation and reforestration is regarded as the decrease of greenhouse effect gas discharge in the Kyoto protocol. Therefore, it is necessary to monitor forest change in a wide area. For the purpose of monitoring forest area change widely, two methods were developed for measuring the crown cover ratio of forest by using aerial photograph or airborne laser scanner. In the further study, the method to measure the diameter at breast height (DBH) of trees was developed by using ground-based laser scanner. We obtained good results, whereas it is necessary to improve and validate these methods.