The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
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This paper describes the dual-view FIGOS data acquisition and 
storage, the generation of metadata and the pre-processing 
applied prior to a BRDF retrieval in the context of the spectral 
database SPECCHIO (Huni et al., 2008), which is used to store 
the according spectral data and metadata. 
Table 2: Illumination and reflection geometry configurations in 
the field case (Schaepman-Strub et al., 2006) 
The hemispherical conical case (Table 2) is the configuration 
that describes the illumination/reflection geometry under field 
conditions. Under clear sky conditions most energy is stemming 
from the direct solar irradiation while a minor part is 
contributed by the indirect radiation originating from scattering 
processes in the atmosphere and from adjacent objects. The 
indirect component is inhomogeneous over the incoming 
hemisphere: largest values are observed close to the direct 
irradiance direction and minimum values in the principal plane 
opposite the sun position. For clarity, we will refer to the 
hemispherical-conical configuration under field conditions as 
“Field HCRF” within this paper. 
2. DATA ACQUISITION AND PREPARATION 
2.1 Data Acquisition 
Acquisition of spectrodirectional datasets is based on the dual 
view FIGOS. Two ASD FieldSpec 3 spectroradiometers 
(Analytical Spectral Devices Inc., 2007) are mounted on a 
sledge running along a zenith arc and capture the down-welling 
(Linc diff) and up-welling (L r ) radiances (Schopfer et al., 2007a). 
Due to saturation and pointing problems, the direct illumination 
E dir is not measured with the upward looking ASD but with an 
MFR sunphotometer (Yankee Environmental Systems Inc., 
2000) that collects the incoming total and diffuse radiance in six 
narrow spectral bands (central wavelengths: 413, 496, 612, 671, 
867, 935 nm) and one broadband channel. 
The BRDF is the most fundamental of the configurations shown 
in Table 1, as all others may be derived from it by integration 
over the illumination and reflection angles. The provision of 
accurate, spectral albedo imagery products (e.g. bi- 
hemispherical reflectance), as is foreseen for the APEX 
(Airborne Prism Experiment, (Nieke et al., 2005)) processing 
facility, depends on knowledge of the BRDF of the sampled 
objects. 
It is thus the goal the retrieve the BRDF from empirical data 
collected under the field conditions, i.e. from Field HCRF data. 
An according retrieval algorithm has been proposed by 
Martonchik (1994) and was experimentally applied to dual 
view FIGOS (Field Goniometer System) data by Schopfer et al. 
(2007a). 
The BRF (Bidirectional Reflectance Factor) is the BRDF 
normalized to the reflectance characteristics of an ideal 
Lambertian reflector (BROr^t,^ = zt' 1 ) and is calculated by 
dividing the BRDF by the factor of 7i. The BRF is retrieved 
from field data by iteratively solving the following equation for 
R (Schopfer et al., 2007a): 
- *,)= a-' 1 • R(e, AA, - K\ EM)+ 
X l i ]r{8,AA-«*,)' L%(0„0„A, - A)- sin (*,)• cos^yw, 
0 0 
(Eq. 1) 
Where 
Q.,Q r = illumination and view zenith angles 
<j). r - <j) {) = illumination or view azimuth angle relative 
to the solar principal plane 
R(0 r , 0 t , <j) - <f>^ = Bidirectional Reflectance Factor (BRF) of 
the target for the given illumination angles. 
Prerequisites of the retrieval are the quantities L r , E dir and 
Lincjiff; which should be measured in the field. However, due to 
the instrumentation used, field data must be subjected to pre 
processing before the retrieval can be started. 
Data collection for one target is usually carried out during one 
day with varying illumination angles, resulting in several dual 
view goniometer data sets. 
2.2 Data Structuring 
Organised data collection 'is an important issue and the 
structuring of the data in a defined way not only helps the 
acquisition process but also aids subsequent data handling. 
The two instruments capturing the incoming and reflected 
radiances are being controlled by two independent laptops. 
Thus, these data must be combined into one dataset before 
loading them into the database. Furthermore, dual-view 
goniometer data sets must be divided into sky/target and 
reference panel measurements. The latter are taken according to 
a predefined sampling protocol and are of importance for (a) 
conversion of radiances to reflectances and (b) calculations 
needed during the pre-processing, as will be detailed later on. 
A hierarchical structure thus holds the data (ASD and MFR 
files) for one target and must be set-up and filled accordingly 
prior to the loading into SPECCHIO (Figure 1). 
▼ m 19.2.2008 
► Si hem_a 
► Si hem_b 
► £i hem_c 
► Si hem_d 
► SB hem_e 
► ¡jjhem_f 
► il hem_g 
▼ Ü hem_h 
▼ Hi incoming 
► Ü reference 
► Qj sky 
▼ in reflected 
► £i reference 
► S target 
▼ m mfr7 
► S3 total 
► S diffuse