E
by the first images (if all goes well!!) from the competing
QuickBird, EROS and OrbView satellites, all of which are
scheduled to be launched during the next few months
before the Congress takes place towards the end of July.
Although the resulting Pan imagery is being labelled as
"high-resolution ",some sense of perspective needs to be
kept about the use of he term in his particular context.
Thus the 1m ground pixel of the new space imagery is
equivalent to that obtainable from modern 1:40,000 scale
aerial photography. Whereas a 20 to 25cm ground pixel
can fairly readily be obtained from 1:10,000 scale aerial
photography and still larger scale photography -in the
scale range 1:3,000 to 1:6,000 -with a 5 to 10cm ground
pixel size is in regular use for the large-scale mapping of
urban areas. Thus the biggest value of the "high-resolu-
tion "space images could well be hat of allowing images
to be acquired for remote areas and over countries that
have severe restrictions regarding the taking and dissem-
ination of aerial photography of heir territory. But the pric-
ing of he new imagery as compared with that of compa-
rable aerial photography will also be a decisive factor in
its take-up. Again this whole matter should become
clearer at the Congress and it will be very interesting to
see how the issue of the Space Imaging company refus-
ing to release the sensor model of IKONOS to the system
suppliers will be resolved.
Imaging Spectroscopy
During the last few years, much of the attention of the
remote sensing community has been given to the devel-
opment of imaging spectroscopy. With this technology, the
imaging of he ground takes place using a scanner that pro-
vides images in a large number of contiguous, narrow, but
discrete spectral bands so that a complete spectrum is
obtained over a wide range of visible and infra-red wave-
lengths for the area being imaged. Usually this technique
is termed hyperspectral imaging with the term "hyper
"replacing "multi "to convey the idea of the much large
number of individual bands or channels being covered as
compared with the small number of much broader bands
used with multi-spectral imagery. To achieve this, suitable
prisms or gratings are used to refract the incoming radia-
tion differentially on o an array of detectors that can cap-
ture the full range of up to several hundred narrow spectral
bands. Much of the impetus for this development has
come from NASA, which has funded the development and
construction of a number of alternative hyperspectral
scanner designs both in-house (e.g. those built by JPL and
GSFO) and by outside contractors (e.g. TRW).
Airborne Hyperspectral Scanners
Although the eventual deployment of these hyperspectral
scanners will be in space vehicles, up till now, almost all of
the existing imagers have been operated from airborne
platforms to prove the design, operation, performance and
reliability of the new systems. Prominent among these is
the Advanced Visible Infra Red Imaging Spectrometer
(AVIRIS) constructed by JPL and operated from high-flying
NASA aircraft. Besides the many NASA sponsored devel-
opments, a number of commercial suppliers -e.g. GER
(USA), ITRES Research (Canada)a nd Integrated Spectron-
ics (Australia) -have entered this field and have sold air-
borne systems to various mining exploration companies
and to government organisations involved in environmen-
264
tal monitoring. One can expect the results from this devel-
opment and its applications to be presented at the Con-
gress. They are eagerly awaited and sought by many field
and environmental scientists.
Spaceborne Hyperspectral Scanners
The story regarding spaceborne hyperspectral devices has
been punctuated by failures and disappointments -as has
so much of optical remote sensing from space in recent
years. In particular, NASA 's Lewis satellite with its two
alternative hyperspectral imagers built by TRW and GSFC
respectively was lost shortly after its launch in August
1997.But a determined effort is now under way to retrieve
this rather dire situation. Thus NASA 's newly launched
Terra satellite has various sensors with multiple band
imaging capabilities in the form of its ASTER, MODIS and
MISR scanners. In two or three months’ time, NASA will
also launch its EO-1 developmental satellite with its
advanced ALI multi-spectral linear array scanner and its
Hyperion hyperspectral imager with 220 spectral bands -
the latter instrument being derived from that lost on the
Lewis satellite.EO-1 will be orbited in formation with both
Landsat-7 and Terra for comparative purposes. Again, if
indeed all goes well, then one can expect the images and
preliminary results from all three satellites to be presented
and discussed before a large audience at the Amsterdam
Congress. In particular, there has been a big revival of
interest with the advent of this latest satellite (L-7) in the
Landsat series.
Furthermore, the availability of its multi-spectral imagery
with its wide ground coverage at a medium resolution and
at a low cost seems certain to be reflected in papers given
in the appropriate technical sessions and in the images
that will be displayed on the stands in the Technical Exhi-
bition.
Radar Imagery
Dealing with microwave radar imagery is not easy -in this
respect, your reviewer still bears the scars of his own con-
siderable involvement with his type of imagery during the
1980s.And there is still no sign of solutions to some of the
fundamental difficulties -including the occurrence of
speckle or clutter; foreshortening; layover; dead areas due
to radar shadow; etc.- that are experienced with this type
of imagery. Notwithstanding your reviewer ’s previous
(poor) experience, it is obvious that currently there is a big
revival of interest in this field. Much of this has been fuelled
by the recent developments in interferometric SAR (INSAR
or IfSAR) for DEM generation. The basic idea is quite an
old one -having been introduced originally by the
Goodyear company in the mid-1970s.However,since then,
the technology and the subsequent processing of the data
have slowly been developed to a much more mature state.
This has resulted in much activity taking place recently
using data acquired both from airborne and spaceborne
platforms. Indeed current interest is literally sky-high -it
really is a hot topic!!
Airborne SAR Imagery
Once again, much of the basic research and development
in this field has been carried out by NASA with JPL to the
fore. This work has resulted in the development of systems
such as the TOPSAR/AIRSAR dual-frequency SAR and the
IFSARE INSAR system (in co-operation with ERIM). The
International Archives of Photogrammerty and Remote Sensing. Vol. XXXIII, Part A. Amsterdam 2000.
