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Title
International cooperation and technology transfer
Author
Fras, Mojca Kosmatin

sensors have their advantages and the most likely
scenario for the future will be an increased emphasis
on data fusion as users select the sensors most likely
to provide their information in each case and rely on
their workstation software to use all the data
together. The two types of data will be
complementary rather than competitive.
2. AIRBORNE DIGITAL SENSORS:
REQUIREMENTS
To have any chance of an impact in a market place
spoilt for decades by high performance film
cameras, an airborne digital sensor must provide:
• large field of view and swath width
• high resolution and accuracy, both geometric
and radiometric
• linear sensor characteristics
• multispectral imagery
• stereo.
The first requirement, however, seems to rule out
area CCD arrays, because readily available models
in mid 1999 are 4Kx4K pixels or less, whereas a
linear array of 12,000 pixels is readily available,
requiring only one third as many flight lines.
Considerable research work has been done in
Germany since the 1970s, which has demonstrated
the suitability of three panchromatic lines on the
focal plane, with additional multispectral lines near
the nadir. This obviates the need for multiple area
arrays to provide a wide field of view and a
multispectral capability (Figure 1). The left-hand
diagram suggest how the focal plane could be
populated using the three line principle: three
panchromatic lines give the geometry and stereo,
whilst additional lines, their sensitivity controlled by
filters, give the multispectral information. In the
right hand diagram, multiple area array CCDs and
lenses are required to provide both the same ground
pixel size and multispectral range as the three-line
approach.
multiple RGB + infrared arrays to
increase FOV
WÊÊMÊMÊÊÊÊÊËËtÊËÊËÈÊÊÊÎ&&iËÊtmËÊÊÊmmÊ0ÊMmm
Fig. /. The alternatives: linear and area CCD arrays.
3. THREE-LINE SCANNER APPROACH
The three-line concept results in views forward from
the aircraft, vertically down and looking backward
(Figure 2). The imagery from each scan line is
assembled into strips (Figure 3). The characteristics
of relief displacement in the line perspective
geometry of the strip approach vis a vis the
conventional central perspective geometry are
indicated in Figure 4, showing the line perspective
geometry of the three-line imagery on the left and
the familiar central perspective geometry of the film
photograph on the right. The angles between the
incoming information to the three lines are, of
course, fixed. With three lines there are three
possible pairings for stereoscopic analysis - strips 1
and 2, 2 and 3, and 1 and 3. With film cameras, the
parallactic angle is a function of principal distance
and airbase. Moreover, every object appears on all
three strips, whereas on film imagery only 60% of
the area of any one photograph is in a triple overlap.