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In: Wagner W., Szekely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B 
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Figure 5 : fAPAR data sets, © 
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3.2 Albedo from SPOT/VGT 
The albedo is the fraction of the incoming solar radiation 
reflected by the land surface, integrated over the whole 
viewing directions. The BioPar albedo products include the 
directional albedo calculated for the local solar noon (also 
called “black-sky albedo), and the hemispheric albedo, 
integrated over the whole illumination directions (also called 
“white-sky albedo”) for 3 broad bands: visible [0.4, 0.7pm], 
near-infrared [0.7, 4pm], and the whole solar spectrum [0.3, 
4pm]. The coefficients resulting from the inversion of a 3- 
kemels linear bidirectional reflectance model on the 
atmospherically-corrected SPOT/VEGETATION reflectances 
(Baret, et al. 2007) acquired during a period of 30 days are 
then combined with the pre-computed values of the directional 
kernels integrated over angular domains to estimate albedos. 
Finally, the broadband albedos are derived by linear 
relationships of spectral quantities. 
The product has the following characteristics (see the PUM 
document on SDI for more details) : reflectance values with 
error and quality flags, spatial resolution 1 km, temporal 
resolution 10 days, geometric accuracy 10%, thematic target 
accuracy 10%, global coverage by square tiles of 10°. 
3.3 Soil Water Index (SWI) 
The Soil Water Index is defined as the soil moisture content (in 
percent) in the soil profile. The retrieval algorithm uses an 
infiltration model describing the relation between surface soil 
moisture and profile soil moisture as a function of time. The 
algorithm is based on a two-layer water balance model 
proposed by Wagner et al. (1999) to estimate profile soil 
moisture from SSM retrieved from scatterometer data. The 
remotely sensed topsoil represents the first layer and the 
second layer extends downwards from the bottom of the 
surface layer. In this model, the water content of the reservoir, 
whose depth is related to a characteristic time length (T), is 
described in terms of an index, which is controlled only by the 
past soil moisture conditions in the surface layer. A