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ground coverage of each frame image produced by such
cameras and the very large numbers of these images
needed to cover any substantial area of terrain, the users
are enthusiastic about this development and can be
expected to share their enthusiasm at the Congress.
Other Airborne Digital Frame Cameras
Going up the scale in terms of CCD array size,4k x 4k =16
Megapixel areal arrays have been utilised in the experi-
mental air-borne digital cameras developed by IGN
(France) and Ohio State University (USA).
Currently at the top of he resolution and format range,
Philips have produced a 7k x 9k =63 Megapixel array and
Lockheed-Martin-Fairchild an 8k x 8k =64 megapixel
array. However the manufacture of such large arrays lies
at the very edge of current chip fabrication technology.
Furthermore, to get such a large number of individual
imaging elements to work properly, each with the same
response and avoiding dead pixels, is very difficult -as is
the radiometric calibration of these sensors. With low
chip yields, this makes large-format CCD areal arrays
very expensive to produce. In this context, there has
never been any question about the adequacy of the geo-
metric resolution of digital cameras -e.g. the Kodak cam-
eras use areal arrays with a 9.2 um pixel size. However
the small array size gives a limited ground coverage,
especially when compared with the 25k x 25k =625
Megapixels of a aerial film camera image digitised at the
same pixel size of 9.2 um. However, of the two major
manufacturers, Z/I Imaging is now taking the plunge into
this area with its new Digital Modular Camera (DMC) con-
cept involving the use of multiple cameras (i) to get over
the ground coverage limitations, and (ii) to produce multi-
band, multi-spectral images. If the actual hardware DMC
camera is shown at the Amsterdam Congress, then it is
certain to be a centre of attention.
SSTL 's Digital Space Cameras
A the same time, in parallel with these air-borne develop-
ments, digital cameras are starting to be mounted in satel-
lites. Thus, for example, low-cost digital cameras
equipped with off-the-shelf 1k x 1k CCD areal arrays from
Kodak and lenses from Leica have been installed and used
in the experimental UoSAT-12 mini-satellite produced by
SSTL in the UK to validate key mini-satellite bus and pay-
load technologies. Even these inexpensively produced
cameras are producing pan images with ground pixel sizes
of 10m (equivalent to that of the SPOT Pan sensor) and
multi-spectral images with a 30m ground pixel (equivalent
to that of Landsat TM) -albeit with limitations in their
ground coverage.
The UoSAT-12 cameras also employ the approach of
sequential exposure of the constituent band images to
produce multi-spectral images -like that adopted on the
Sensys Technologies AA 497 airborne camera mentioned
above. Whereas, in the earlier SSTL TM-Sat, three sepa-
rate cameras are being used to produce the component
band images simultaneously to create multi-spectral
images -in a similar manner to that proposed with Z/I
Imaging 's DMC camera.
Other Space-borne Cameras
Digital cameras using areal arrays were also installed in
EarthWatch 's EarlyBird satellite. Unfortunately, although
International Archives of Photogrammerty and Remote Sensing. Vol. XXXIII, Part A. Amsterdam 2000. —
the satellite was launched successfully in December
1997,the on-board power supply failed four days later. A
similar camera was to have been mounted in NASA 's
Clark satellite. However, in February 1998,the project was
terminated due to cost overruns and the delays associated
with the non-availability of the launcher. In summary,
regarding future prospects in this field, the new digital
cameras with areal arrays that will be discussed at the
Amsterdam Congress are just the beginning of this devel-
opment.
There is still a long way to go before these digital cameras
can compete directly with current large-format film cam-
eras: in this respect, everything is dependent on the suc-
cessful development of larger areal arrays and their avail-
ability in quantity at a reasonable cost.
Airborne Pushbroom Scanners
At Amsterdam, we shall also see the entry of the airborne
pushbroom scanner based on the use of linear CCD arrays
into the mainstream of photogrammetry. The technology
has undergone a long gestation period. The original con-
cept of the three-line scanner with fore/nadir/aft pointing
allowing along-track stereo-imagery to be acquired both
from the air and from space is that devised by Hofmann in
1972 and has been nurtured ever since by the German
Aerospace Centre (DLR). Under its sponsorship, in parallel
with the development of the technology for use in the
MOMS,MEOSS,Mars96 and Mars Express space mis-
Sions, a series of airborne versions of the three-line scan-
ner have also been built. These have included the EOS (in
1978), the Digital Photogrammetric Assembly (DPA), the
Wide-Angle Airborne Camera (WAAC) and, most recently,
the High-Resolution Stereo Camera (HRSC). The use of
the last of these (the HRSC-A) by DLR and the French
ISTAR company has resulted in a series of most impres-
Sive mapping products, including high-resolution multi-
spectral orthoimages and DEMs.
Now the technology has been taken up by the second of
the two major aerial film camera manufacturers, LH Sys-
tems. The results achieved with the engineering version
of the company 's new scanner installed in a gyro-con-
trolled mount and utilising a 12,000 pixel linear array with
a pixel size of 6.5 um were shown publicly at the begin-
ning of 1999.A further prototype model was flown in Jan-
uary 2000.If,as promised, the production version of the
imager featuring a multi-spectral capability with four lines
recording images simultaneously in the blue, green, red
and near-IR bands and the use of 20,000 pixel arrays in
each line does appear, then undoubtedly it will be
another star attraction in the Technical Exhibition at the
Congress.
Space Pushbroom Scanners
Here he emphasis will almost certainly be on the prod-
ucts from the new high-resolution space imagers. After
the protracted development of the technology and sev-
eral disappointments over failed launches, at last, Space
Imaging 's IKONOS with its Kodak-built pushbroom
scanner -whose pan sensor is equipped with a 13,500
pixel linear array with a 12 (m pixel size - has been placed
successfully in orbit and has come into commercial oper-
ation. Certainly we should expect to see and hear a great
deal about the products and the applications of the
IKONOS imagery at the Congress. This will be reinforced
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