The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
for a long time suffers from severe Alpine conditions (wind, ice 
and snow storms) and root-rot fungi is gradually reshaped into a 
highly heterogeneous, woody forest. Furthermore, examples of 
mature forests prone to insect defoliation demonstrate that 
woody parts may dominate the canopy cover already earlier in 
the development phases coniferous canopies (e.g. Radelhoff et 
al., 1999). 
Needle chlorophyll content of these forests can be detected and 
mapped by fine-resolution satellites such as CHRIS-PROBA. 
Further, it has been demonstrated (Rautiainen et ah, 2008; 
Verreist et ah, 2008) that CHRIS data with its relatively small 
pixel resolution (-17.0 m) matches well with radiative transfer 
models that provide scene-based BRF data of stands. 
Modeling results without background contamination 
demonstrate that nearly all real-world structural features match 
to quasi-optimal conditions for detecting and mapping 
chlorophyll from reflectance data as long as the fractional NPV 
fractional cover is low. In denser canopies a passive sensor 
cannot penetrate through tree crowns and detect signatures 
directly under tree canopy so the contribution of a background 
is of less importance in determining the Cab-related spread. In 
sparse canopies (CC<40%), however, the background signal 
may either act as an additional distorter (when ground cover is 
e.g. litter, bare soil) or contribute to the Cab variability (when 
ground cover is e.g. grass, shrubs), or may even be composed in 
a similar manner as the overstory (e.g. mixture of PV and NPV). 
The latter is the case in old-growth forests. Conclusively, 
modeling results demonstrated that canopy composition is the 
key player in determining the success of Cab retrieval. Within 
the scope of leaf-to-canopy upscaling problem, further efforts 
should be devoted to the robustness of chlorophyll retrieval 
techniques, with special attention to correct for fractional wood 
cover. 
Figure 4. The four study sites (a) young Norway spruce stand, b) old-growth forest, c) early mature beetle-infected 
lodgepole pine and, d) mature beetle-infected Norway spruce) positioned within the three landscapes of 
plausible canopies(e: CC vs. crown LAI; 
e, f, g: CC: 0.60; LAI: 2.5) 
ACKNOWLEDGEMENT 
The work of J. Verreist was supported through the Dutch SRON 
GO programme (Grant-No. EO-080). 
REFERENCES 
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