ground track. This unique side-looking capacity of SPOT is
important for monitoring applications requiring high frequency
of coverage, such as natural disasters. Furthermore, it enables
production of SPOT stereo-images, by recording the same
ground scene from two different satellite locations. They are
increasingly used for production of digital elevation models
(DEM) and for 3-dimensional viewing of the object scene.
SPOT 4 is scheduled for launch in 1997 (Section 3.4).
2.5 Other Ongoing Satellite Programs
Significant civilian EO satellite programs are operated by the
space agencies of India, Japan and Russia, as well as by the
European Space Agency (ESA). However, RS data from these
programs are not as widely available for operational
applications at regional and global levels as the data from the
programs described above. This is partially due to the
experimental nature of some of these programs, difficult
access to their data and gaps in their global coverage because
of an incomplete network of ground receiving stations and lack
of onboard data recorders. This situation is quickly changing,
helped by international agreements for data reception,
marketing and distribution. It is expected that the future
contributions by some of these programs to regional and global
mapping and monitoring activities will grow significantly.
2.6 Global Positioning Systems
The potential of satellite remote sensing for mapping and
monitoring at regional and global levels has been further
enhanced by the growing operational use of the space-based
Global Positioning System (GPS). Developed by the United
States for military applications in the mid-1970s, a
constellation of 21 geostationary GPS satellites, with 3 spares
in orbit, enables near instantaneous determination of positions
anywhere on the earth's surface. GPS continuity is assured
because the first satellites of the next-generation GPS are
ready for launch. Russia is deploying a similar satellite
positioning system called the Global Navigation Satellite
System (GLONASS).
Portable and relatively inexpensive GPS receivers are
increasingly used for quick completion of mapping control,
preparation of base maps, and for the precise geometric
rectification and positioning of image data recorded by
satellites. (Clavet et al, 1993). This is of particular
importance in developing countries where the existing
mapping control is often incomplete or unreliable. Hence, the
GPS have become essential and effective tools for verification
and, when necessary, completion of existing mapping control.
Their use will assure that the compilation of base maps is
done with uniform geometric accuracy for the whole region.
2.7 Geographic Information Systems
Other important developments, effecting the implementation
of large mapping and monitoring programs, have been the
expanding capacity and user-friendliness of Geographic
Information Systems (GIS), accompanied by their decreasing
price. EO satellites provide a source of RS data, while GIS
provide the capacity for integration of geo-referenced data
from different sources, their joint analysis and generation of
cartographic, statistical and modeling products from integrated
and harmonized databases.
Integration of remote sensing data with other relevant
geographically referenced data, such as topographic, soils,
climatic, demographic, etc. in GIS, increases the quantity as
well as the quality of the derived information. Some GIS
software packages also provide a mathematical modeling
capacity for the analysis of trends, environmental impact
assessment, agricultural drought forecasting, etc. Thus, GIS
facilitate the transformation of geospatial data into
information, knowledge, and, ultimately, decisions. However,
it should be remembered that the usefulness and impact of GIS
depend on the quality of the input data. Even the most
sophisticated GIS are useless if no reliable input data are
available. Furthermore, there is a need for the development of
innovative procedures for interpretation and analysis of
integrated multi-source RS data, in particular for combined
analysis of optical and SAR RS data, resulting in their more
effective and efficient applications.
2.8 RS Data Archives and Information Networks
Effective dissemination of information on RS data, and user-
friendly access to data archives worldwide have become
priority requirements by decision-makers responsible for land
cover mapping, natural resources assessment and
environmental monitoring programs. The impact of these
programs, and thus their success, will depend on the extent to
which their products will be used. In order to speed up and
facilitate this process, the following approach should be
followed:
(a) establishing user-friendly data archives and effective
information networks;
(b) establishing a clear copyright policy;
(c) establishing a reasonable pricing structure;
(b) training of prospective users of new products.
The number of countries which have established information
networks for RS data and derived products is steadily
increasing. Furthermore, those networks are being linked to
provide access to foreign data archives. Examples of such
state-of-the art RS information networks were selected from
Canada and the United States.
Since 1990, the Canada Centre for Remote Sensing (CCRS)
has been operating a dedicated RS information network, the
GCNet. It serves as one-stop-shop for information on RS data,
products, services and publications. It also provides a link to
the International Directory Network (IDN) operated by the
Committee on Earth Observation Satellites (CEOS). The IDN
is a global network with three regional coordinating nodes
located at NASA (USA), ESA-ESRIN (Italy) and NASDA
(Japan). Since 1995, the GCNet has been accessible on World
Wide Web. The capacity of GCNet will be significantly
upgraded and broadened when its follow-on system, the
Canadian Earth Observation Network (CEONet) becomes
operational in 1998. It will provide a state-of-the art, fast
interface between the geospatial data archives and their users
in Canada and abroad. (Cihlar et al., 1994; Fisher et al., 1995;
Kalensky, 1996).
One of the most important components of the Earth Observing
System (EOS), planned by the United States National
Aeronautics and Space Administration (NASA), will be the
EOS Data and Information System (EOSDIS). The EOSDIS
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
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