Definitions - Information Fusion in Signal and Image Processing - page 3

methods rather than systems. It is better suited to the diversity of situations encoun-
tered in signal and image processing. In this sense, it is a broader definition.
Another European workgroup of the EARSeL (European Association of Remote
Sensing Laboratories) extended the JDL's definition to the broader field of satellite
imagery [WAL 99]: the fusion of data constitutes a formal framework in which the
data originating from different sources can be expressed; its goal is to obtain infor-
mation of higher quality; the exact definition of “higher quality” will depend on the
application. This definition encompasses most of the definitions suggested by several
authors in satellite imagery, which are gathered in [WAL 99]. Definition 1.1 goes fur-
ther and includes decisions.
The meaning of the word fusion can be understood on different levels. Other con-
cepts, such as estimation, revision, association of data and data mining, can sometimes
be considered as fusion problems in a broad sense of the word. Let us specify these
concepts.
Fusion and estimation. The objective of estimation is to combine several values
of a parameter or a distribution, in order to obtain a plausible value of this parameter.
Thus, we have the same combination and decision steps, which are the two major
ingredients of Definition 1.1. On the other hand, numerical fusion methods often
require a preliminary step to estimate the distributions that are to be combined (see
section 1.5) and the estimation is then interpreted as one of the steps of the fusion
process.
Fusion and revision or updating. Revising or updating consists of completing or
modifying an element of information based on new information. It can be consid-
ered as one of the fields of fusion. Sometimes, fusion is considered in a stricter sense,
where combination is symmetric. As for revision, it is not symmetric and it draws a
distinction between information known beforehand and new information. Here, we
will be considering dynamic processes among others (particularly robotics), and it
seems important for us to include revision and updating as part of fusion (for exam-
ple, for applications such as helping a robot comprehend its environment). Revision
involves the addition of new information that makes it possible to modify, or specify,
the information previously available about the observed phenomenon, whereas updat-
ing involves a modification of the phenomenon that leads to modifying the information
about it (typically in a time-based process).
Fusion and association. Data association is the operation that makes it possible
to find among different signals originating from two sources or more those that are
transmitted by the same object (source or target). According to Bar-Shalom and Fort-
man [BAR 88], data association is the most difficult step in multiple target tracking.
It consists of detecting and associating noisy measurements, the origins of which are