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corrections, etc., if necessary. The alignment problem calls 
upon physics, and is certainly the problem in data fusion which 
is the most relevant to the concerns of the remote sensing 
community. 
5. CONCLUSIONS 
A new definition of the data fusion has been proposed which 
better fits the remote sensing domain. Data fusion should be 
seen as a framework, not merely as a collection of tools and 
means. This definition emphasizes the concepts and the 
fundamentals in remote sensing. Several other terms are also 
proposed most of which are already widely used in the 
scientific community, especially that dealing with information. 
The establishment of a lexicon or terms of reference allows the 
scientific community to express the same ideas using the same 
words, and also to disseminate their knowledge towards the 
industry and ’customers’ communities. Moreover it is a sine qua 
non condition to set up clearly the concept of data fusion and 
the associated formal framework. Such a framework is 
mandatory for a better understanding of data fusion 
fundamentals and its properties. It allows a better description, 
using similar terms clearly understood by everybody, of the 
potentials of synergy between remote sensing data, and 
accordingly their better exploitation. 
The problem of alignment of the information to be fused is very 
difficult to tackle. It is a pre-requisite to any fusion process and 
should be considered with great care. The remote sensing 
community may play a role in that domain, since it has a great 
experience in both the physics involved, including sensors, and 
the mathematical operations of sampling. 
Finally, the introduction of the concept of data fusion into the 
remote sensing domain should raise the awareness of our 
colleagues on the whole chain ranging from the sensor to the 
decision, including the management, assessment and control of 
the quality of the information. 
ACKNOWLEDGEMENTS 
This work has been made thanks to many fruitful discussions 
with several researchers and the many participants to the 
EARSeL - SEE working group "data fusion". I also thank Luce 
Castagnas, Isabelle Couloigner, Louis-François Pau, and Stelios 
Thomopoulos for their comments and assistance. 
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