Ulla Pyysalo

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Extracting forest variables from airborne laser scanner has less than 10 years of history. During that time, however, a new area in the field of forest studies has emerged. This paper describes existing algorithms and methods of airborne laser scanning that are used for forest measurements. The methods are divided into the following categories: 1)(More)
We present a new approach for radiometric calibration of light detection and ranging (LIDAR) intensity data and demonstrate an application of this method to natural targets. The method is based on 1) using commercially available sand and gravel as reference targets and 2) the calibration of these reference targets in the laboratory conditions to know their(More)
We have studied the possibility of calibrating airborne laser scanning (ALS) intensity data, using land targets typically available in urban areas. For this purpose, a test area around Espoonlahti Harbor, Espoo, Finland, for which a long time series of ALS campaigns is available, was selected. Different target samples (beach sand, concrete, asphalt,(More)
This paper evaluates and discusses the accuracy of laser scanner in DTM (digital terrain model) generation and digital 3-D height model generation in forested areas. High-pulse-rate laser scanners are capable of detecting single trees in a boreal forest zone, since a significant amount of the laser pulses reflect directly from the ground without any(More)
Radiometric calibration of airborne laser scanning (ALS) intensity data aims at retrieving a value related to the target scattering properties, which is independent on the instrument or flight parameters. The aim of a calibration procedure is also to be able to compare results from different flights and instruments, but practical applications are sparsely(More)
In this paper, we present a method for 3D volumetric reconstruction of landscape from airborne laser scanner data. The method applies a voxel model, where volume is divided to sub-volume particles, voxels, associated with a scalar or vector value. In the presented study the voxel model is generated from airborne laser scanner data, which enables measurement(More)
A method based on extracted trunks is proposed for automatic determination of corresponding trees between a georeferenced pair of terrestrial images and airborne laser scanner data in a wooded area. Trunks in the terrestrial images are obtained by region growing segmentation between left and right edges of trunks detected within a region of interest. Trunks(More)
A method to measure tree crown dimensions is introduced in this article. The method is based on terrestrial images, which are captured from two different directions. Image orientation is registered during the image acquisition and this geometrical information is utilized in image pre-processing. In pre-processing images are corrected from distortion errors(More)