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Figure 3b The same image as in figure 3a, but overlaid with administrative units 
environmental indicators and provides standardised information 
for the total extent of the area included. 
The two-step procedure offers the advantages of quickly 
providing an overview of changed regions and of limiting the 
time needed for change identification by excluding unchanged 
regions. 
Spatial units used should be related to the process studied, 
otherwise change interpretation is hampered. When the unit is 
heterogeneous from a process point of view, observations can 
be ambiguous. 
The change detection procedure is easy to apply. It could be 
used in other applications as well, as long as the spatial units are 
related to the process studied. 
The yield indicator is the most time consuming part of the 
method, because actual weather data and actual yield data need 
to be collected. When future developments provide accurate 
crop-specific biomass estimations from remote sensing images, 
this will be partially solved. 
Validation of the method has not been finished yet, so it is still 
unknown whether this promising method indeed can live up to 
the expectations. 
ACKNOWLEDGEMENTS 
This research forms part of my PhD-project which is financed 
by the National Institute of Public Health and Environment of 
The Netherlands (RIVM). NOAA-AVHRR image are provided 
by the Joint Research Area in Ispra, Italy. 
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