PRE-PROCESSING OF DUAL-VIEW FIGOS DATA: TOWARDS OPERATIONAL BRDF 
RETRIEVAL 
A. Hueni a *, J. Schopfer a , D. Schlâpfer a , M. Kneubuehler a and J. Nieke b 
a Remote Sensing Laboratories, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland. - 
(ahueni, jschopf, dschlapf, kneub)@geo.uzh.ch 
b ESA-ESTEC, Noordwijk, The Netherlands, -jens.nieke@esa.int 
KEY WORDS: Spectral Database, Metadata, Spectral Processing, BRDF 
ABSTRACT: 
The Bidirectional Reflectance Distribution Function (BRDF) is an inherent property of natural and manmade materials. Its effects 
depend on the illumination/observation geometry and wavelengths and are apparent in groundbased, airborne and spacebome 
imagery. The BRDF is a fundamental quantity from which all other illumination/reflection configurations can be derived. 
Calibration and validation of hyperspectral images requires knowledge of the BRDF if spectrodirectional effects are to be accounted 
for. The BRDF can be retrieved from dual-view field goniometer system (FIGOS) data, which is stored in the spectral database 
SPECCHIO. The retrieval must be precluded by pre-processing steps, which apply transformations on the raw field data and 
according metadata. SPECCHIO has been updated to support such pre-processing. Intercalibrations of the involved instruments and 
temporal corrections lead to a network of operations to be applied to the input data. A generalisation of the processing has led to the 
concept of the Space Processing Chain, allowing the flexible combination of modules to form complex processing flows as required 
by the goniometer data pre-processing. The newly added support of intercalibration factors in the SPECCHIO data model will be an 
important asset in future round robin experiments. The Space Chain approach will operationalise the retrieval of BRDF from dual 
view FIGOS data and generally increase the usefulness of the SPECCHIO system by the introduction of user configurable 
processing. 
1. INTRODUCTION 
The BRDF (Bidirectional Reflectance Distribution Function) is 
an object inherent property and describes the dependency of an 
observed reflectance on the wavelength and the illumination 
and observation geometry (Nicodemus et al., 1977). BRDF 
effects can be readily identified in airborne and satellite 
imagery and do hinder the straightforward utilization of such 
data for subsequent analysis, as identical objects can appear to 
have differing spectral signatures. The severity of surface 
specific BRDF effects in airborne imagery is dependant on the 
field of view (FOV), observation direction and orientation of 
the flight strip relative to the sun. Effects are most pronounced 
with large FOVs and flight directions perpendicular to the solar 
principal plane (Beisl, 2001). 
Correction of BRDF effects in imagery requires knowledge of 
the BRDF of the involved objects to validate or parameterise 
according algorithms. The acquisition of spectrodirectional in 
situ data is a part of the calibration and validation (CalVal) 
activities carried out by the Remote Sensing Laboratories (RSL) 
(Nieke et al., 2007; Schopfer et al., 2007b). 
Table 1 illustrates the possible combinations of conceptual 
illumination and reflection geometries according to Nicodemus 
(1977). An isotropic illumination L t is assumed for these 
configurations. 
Cm** 
Hgnnetoásmt 
L ? 
\yj. .. 
/% ■ \ 
/ « * , \ 
31 
a* 
i 
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¡ 
L i. \ 
yJiJ. ^ 
l 4 j 
«S«***»- 
'* ^ 1 y 
l " ~ « ^ 
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Table 1: Illumination and reflection geometries (adapted from 
Nicodemus et al. (1977)) 
From a geometry point of view, the hemispherical conical 
configuration describes the field case where the incoming 
radiance originates from the sky (i.e. hemispherical 
illumination) and the reflected radiance is sampled by an 
instrument with a finite detector size, i.e. the target with area 
dA reflects radiance into a solid angle towards the detector. 
However, irradiance under field conditions is a mixture of 
directional and diffuse, non-homogenous, hemispherical 
components as shown in Table 2 (Schaepman-Strub et al., 
2006). 
Corresponding author.