— 
is context 
ies of the 
, Shashua 
Which is 
> used for 
algorithm 
n by any 
s) and the 
the course 
1ische 
orkshop 
pringer. 
Vol. 293, 
“omputer 
“onf. on 
> of 
weft 23 der 
st? 
etry. 
nding 
A. Rothkirch 
BRDF MEASUREMENTS OF URBAN SURFACE MATERIALS AT THE EGO FACILITY USING A 
LASER SOURCE 
André ROTHKIRCH, Gerhard MEISTER, Hartwig SPITZER, Johann BIENLEIN 
CENSIS, II. Institute for Experimental Physics, University of Hamburg, Germany 
Mail: c/o KOGS, FB Informatik, Vogt-Koelln-Str. 30, D-22527 Hamburg, Germany 
www: http://kogs-www.informatik.uni-hamburg.de/projects/censis/remotesens. html 
Email: rothkirc @informatik.uni-hamburg.de 
KEY WORDS: BRDF, Laser, EGO Goniometer, Polarization, Diffuse scattering. 
ABSTRACT 
In this paper we present a study of the BRDF characteristics of urban surface materials (e. g. roof coverings). Multiangular 
measurements were made at the European Goniometer Facility, Ispra, Italy. We used a linearly polarized HeNe-laser as 
illumination source and a spectroradiometer with a mounted polarizer as detector. Measurements were done at horizontal 
(s) and vertical (p) polarisation states relative to the principal plane, resulting in measurements at four different combina- 
tions of source and detector orientation (ss, sp, ps and pp). We performed a systematic study of the accuracy of BRDF 
measurements to determine measured deviations from the Lambertian case. Polarization effects in the principal plane 
are analyzed for roof covering materials as well as for a Spectralon sample of 50% reflectance. The measurements show 
that the reflectance from our surface materials is a combination of different components. As a first approximation they 
can be described by a component due to internal scattering (diffuse component) and a component that is due to specular 
reflection of inclined surface facets. 
1 INTRODUCTION 
Remotely sensed multitemporal images allow, for example, analyses of urban infrastructure using computer based change 
detection (Wiemker et al., 1997), (Wiemker, 1997a). Usually, the images are taken at different illumination conditions 
(Le. different incident sun zenith angle) and observation geometries which is why a transformation of the measured 
radiances into reflectances is done commonly using atmospheric radiative transfer models to be independent of such 
influences. Change detection is furthermore complicated by non-lambertian scattering characteristics, i.e. the intensity of 
the reflected radiance depends on the viewing geometry and is not only a function of the cosine of the incident irradiance. 
The directional dependencies of light reflected from a surface are described by the Bidirectional Reflectance Distribution 
Function BRDF as defined by (Nicodemus, 1970). 
As part of our research program we conducted measurements of the BRDF of urban surface materials using laboratory 
and field measurements as well as airborne multispectral imagery ((Meister et al., 19982), (Meister et al., 2000), (Meister 
etal., 1999), (Rothkirch et al., 1998)). In this paper we present results of laboratory BRDF measurements using polarized 
light. 
2 MEASUREMENTS 
Measurements were made at the EGO Goniometer at the Joint Research Centre, Ispra, Italy. We used a beam expanded, 
linearly polarized HeNe-laser at a wavelength A = 632 nm as illumination source. A SE590 spectroradiometer (Spectron 
Eng., 1987a) with a mounted polarizer was used as detector. Measurements were done at horizontal (s) and parallel (p) 
polarisation states, yielding measurements at four different combinations of source and detector orientation (ss, sp, ps and 
pp). 
Al Instrumentation 
The EGO Goniometer is illustrated in fig. 1. Two quarter-arcs are mounted on a base azimut arc of about 4 m diameter. 
The arc carrying the source is fixed in azimut, the detector arc can be moved covering most azimut positions. Source and 
detector can be moved in zenith angle (source up to 65°, detector up to 70°). A full description of the setup has been 
given by (Koechler, 1994). Sensitivity studies using unpolarized light have been reported by (Solheim et. al., 1996) and 
(Sandmeier et al., 1997) 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 777