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INTENSITY NORMALIZATION BY INCIDENCE ANGLE AND RANGE 
OF FULL-WAVEFORM LIDAR DATA 
H. Gross, B. Jutzi, U. Thoennessen 
FGAN-FOM, Research Institute for Optronics and Pattern Recognition GutleuthausstraBe 1, 76275 Ettlingen, Germany 
- (gross,jutzi,thoe)@fom.fgan.de 
Commission IV, WG IV/3 
KEY WORDS: Laser Data, Full-Waveform, Point Clouds, Intensity, Normalization, Covariance, Eigenvalues, Lambertian Law. 
ABSTRACT: 
The analysis of LIDAR data to extract surface features is of great interest in photogrammetric research. Our investigations show that 
the same material of a surfaces (e.g. gabled roof) yields to different measured values for the intensity due to the incidence angle. 
These values are strongly correlated to the incidence angle of the laser beam on the surface. Therefore we improve the value of the 
intensity by considering the incidence angle derived by the sensor and object position as well as its surface orientation. The surface 
orientation is estimated by the eigenvectors of the covariance matrix including all object points inside a close environment. The 
adaptation of vegetation areas is disregarded. After these improvements the intensity does no longer depend on the incidence angle 
but may be influenced by the material of the object surface only. The surface characteristic depends on the used wavelength. A 
measurement campaign was carried out to investigate the influences of the incidence angle on the measured intensity. By 
considering the incidence angle and the distance between sensor and object the laser data captured from different flight paths (data 
stripes) can be successfully fused. In our experiments it could be 
areas are improved. 
1. INTRODUCTION 
The high potential of laser scanning data for the automatic 
generation of 3d models has been demonstrated in the past 
(Brenner et al., 2001; Geibel & Stilla, 2000; Gross et al., 2005). 
Spacebome, airborne as well as terrestrial laser scanning 
systems allow a direct and illumination-independent 
measurement from 3d objects in a fast, contact free and accurate 
way. 
The latest developments of commercial airborne laser scanners 
allow recording the waveform of the backscattered laser pulse, 
namely the LEICA ALS-50II, OPTECE1 ALTM 3100, 
TOPEYE MK II, and TOPOSYS HARRIER 56. The latter one 
is based on the RIEGL LMS-Q560. In addition to the 
mentioned airborne laser scanners, the prototype of the 
terrestrial laser scanning system ECHIDNA (Lovell et al., 2003) 
has the opportunity to capture the waveform too. 
To interpret the received waveform of the backscattered laser 
pulse, a fundamental understanding of the physical background 
of pulse propagation and surface interaction is important. The 
waveform includes imlicit information about different features 
like the range, elevation variations, and reflectance of the 
illuminated surface based on the inclination between the 
divergent laser beam and object plane. Additonally the received 
waveform depends on the wavelength of the emitted laser light. 
The waveform of each pulse is described by a series of range 
values combined with amplitude values and can be 
approximated by one or more parameterized Gaussian curves 
(Hofton et al., 2000; Persson et al., 2005; Wagner et al., 2006). 
Due to this approximation the temporal position, width and 
amplitude caused by the object surfaces are estimated (Jutzi & 
Stilla, 2006). With these parameters the geometry and the 
reflectance of the illuminated surface can be investigated. 
shown that the normalization of the intensity for the investigated 
The material reflectance features from the measured data 
mainly depends on the incidence angle of the beam on the 
surface, the surface properties and the laser wavelength 
(Jelalian, 1992). 
In the terminology of laser scanning the reflectance is widely 
used as synonym for the amplitude or energy, where the energy 
of each pulse is the integral over its waveform. For a Gaussian 
pulse this can be simplified and approximated by the product of 
amplitude and width. Beside this the term intensity is used for 
the amplitude or energy. 
Various studies about surface reflectance and the related 
intensity have been published in the literature: 
• Hofle & Pfeifer (2007) showed a data and a model- 
driven method for correcting the intensity for specific 
influences. The corrected intensity is successfully 
used to generate intensity images with lower 
systematic errors. 
• Katzenbeisser (2003) introduced for flat surfaces that 
the measured intensity provide a reasonable mean for 
the reflectance, if the measured intensity is corrected 
by the known distance. 
• Kukko et al. (2007) measured for various urban 
materials the dependency of the intensity from the 
incidence angle. 
• Pfeifer et al. (2007) studied the influence on the 
intensity for surfaces with varying incidence angles, 
known reflectance and scattering characteristics. It is 
shown that the range dependent inverse-square model 
might be insufficient to estimate the accurate intensity. 
• Reshetyuk (2006) investigated for various materials 
the surface reflectance and its influences on the 
measured range and intensity.