Use of Naturally Available Reference Targets to Calibrate Airborne Laser Scanning Intensity Data

Abstract

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, different types of gravel) were collected and measured in the laboratory. Using tarps, which have certain backscattering properties, the natural samples were calibrated and studied, taking into account the atmospheric effect, incidence angle and flying height. Using data from different flights and altitudes, a time series for the natural samples was generated. Studying the stability of the samples, we could obtain information on the most ideal types of natural targets for ALS radiometric calibration. Using the selected natural samples as reference, the ALS points of typical land targets were calibrated again and examined. Results showed the need for more accurate ground reference data, before using natural samples in ALS intensity data calibration. Also, the NIR camera-based field system was used for collecting ground reference data. This system proved to be a good means for collecting in situ reference data, especially for targets with inhomogeneous surface reflection properties.

Automated road markings extraction from mobile laser scanning data

“…The intensity values are required to be normalised with respect to these factors prior to the threshold implementation or the use of a range dependent threshold approach is recommended for segmentation or feature extraction (Vosselman, 2009). Most of the approaches used for normalising their values are based on using models and data driven methods (Pfeifer et al, 2008;Jutzi and Gross, 2009;Oh, 2010) while other approaches are based on using external reference targets of known reflectivity behaviour Vain et al, 2009). The intensity attribute can be used to distinguish road markings from the road surface.…”

Alignment of Hyperspectral Imagery and Full-Waveform Lidar Data for Visualisation and Classification Purposes

“…Further, the intensities recorded are not calibrated. As mentioned at Vain et al (2009) the emitted radiation of the pulse is usually unknown in Airborne laser scanning system and it depends on the speed or height of the flight.…”

Correcting Airborne Laser Scanning Intensity Data

“…Intensity values start to decrease significantly from 20 degrees . The range correction or sometimes also called sperical loss can be written (Vain et al, 2009):…”

“…It means that the knowledge about the moisture level in the target is important. For this purposes a camera-based solution was introduced (Vain et al, 2009) with calibration frame. This helps to make in-situ measurements that are more realistic than laboratory measurements, because the conditions are more close to the actual ones.…”

“…The PRF settings should be selected according to the vegetation density and application purposes. For correcting intensity data for different energy levels, a simple formula is used (Vain et al, 2009):…”