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Remote sensing for resources development and environmental management
Damen, M. C. J.

While air photography evolved into remote sensing,
the field of photo-interpretation widened to become
These developments are clearly mirrored in the
subject matter presented at this, the seventh sympo
sium of Commission VII. The number of contributions
is almost tripled compared to 1962, a fact that is
indicative of the growing inportance of remote sen
sing for resource assessment. About one-third of
these contributions (as compared to 4% in 1962)
relate to technical aspects concerning, e.g., the
hard and software used for the job. This trend is
indicative of the spectacular technological growth
in the field of space research and remote sensing in
the past 24 years.
When looking at the fields of applications, the
marked increase of papers related to remote sensing
of renewable resources deserves mention. This fact
is readily explained by the introduction of multi-
spectral remote sensing techniques which allow for
reliable and even semi-automatic detection of crops,
vegetation types, etc. This field has expanded sub
stantially in recent years. The same techniques have
also furthered remote sensing of surface water fea
tures including water pollution. Contributions on
the use of remote sensing for surveying non-renew
able resources are distinctly less numerous. Al
though this may in part be due to competition with
other conferences, it is certainly also related to
the fact that these resources normally cannot be
directly detected on the basis of their spectral
characteristics, although they may (or may not) be
reflected in the spectral signatures of their veg
etation or soil cover. Advances in this field are
thus less distinct and await the inpulses provided
by the stereoscopic satellite images that recently
have become available and that are essential for
earth science application of satellite imagery.
While in 1962 emphasis was on detailed surveys
many papers of 1986 deal with small-scale and
medium-scale resource mapping projects. This is
quite logical taking into account the fact that in
1962 aerial photographs were practically the only
available tool, whereas the imagery of the first-
generation high-resolution resource satellites, with
a spatial resolution of about 80 meters, invites
reconnaissance studies of large areas: More detailed
studies require the additional use of aerial photo
graphs in multi-phase approaches.
It is of considerable interest in this context
that earlier this year the first operational second-
generation high-resolution satellite (SPOT) has
become operational. The merits of these images, with
a spatial resolution of 10 meters panchromatic and
20 meters colour and the potential of the stereo
scopy that can be obtained, have been amply discuss
ed during this symposium. One may thus say with
justification that also this seventh symposium of
Commission VII is taking place on the threshold of a
new era of satellite remote sensing in much the same
way as the first one coincided with an earlier major
Monitoring and updating of maps using recurrent
passes of high-resolution sun-synchronous satellites
is the subject of several papers and relate to
matters such as coastal development, river floods,
A number of authors have made use of images/data
recorded by (NOAA) weather satellites which charac
teristically have a low spatial resolution and a
high temporal resolution. These images have lured
meteorologists and oceanographers into the use of
satellite imagery, thus considerably widening the
circle of scientists engaged in remote sensing ap
plications. In addition, these images serve a var
iety of other purposes, such as the monitoring of
vegetation changes, drought and desertification and
they are even used in the context of locust control.
Although not all these subjects may have received
equal weight during this symposium, the applicabili
ty of low resolution satellite imagery as a coun
terpart of the second generation high-resolution,
stereoscopic SPOT satellite data is fully realised
by the participants. There has been made no mention
of applications of extra-terrestrial remote sensing
during this symposium, although this imagery is now
available from the moon, a number of planets and
planetoids and some of the moons of other planets.
Some may consider this a lack of scientific imagin
ation from the side of the participants while
others may see it as reflecting a (too) low assess
ment of extra-terrestrial (e.g., mineral) resour
When considering the developments of the last few
decades in a more general sense the following main
trends emerge:
A great diversification of sensors that has freed
us from the limitations of the narrow visible spec
trum and that now enable recording in all usable
parts of the electro-magnetic spectrum from the
micro waves, through the thermal infrared zone and
the visible spectrum to the ultra-violet.
A great diversification of recording altitudes
which —leaving for a moment the extra-terrestrial
recordings— now range from an altitude of 36,000
km for the geo-stationary (weather) satellites and
an altitude of approximately 700-900 km for orbit
ing (e.g., sun-synchronous) satellites to 250-300
km for the space shuttle and approximately 18,000-
200 meters for survey aircraft that include super
altitude (stratospheric), conventional, low-flying
reconnaissance and ultralight planes.
Repeated recording at regular relatively short
intervals became common practice. The possibilities
for sequential interpretation of aerial photographs
limited by a recording interval of usually years or
decades is surpassed by the orbiting resource
satellites giving a temporal resolution of less
than one to several weeks (or, if cloud cover in-
terfers: months) and by the geo-stationary satel
lites that record near-continuously (interval of a
few hours or days). There is, of course, a trade
off here between spatial resolution and temporal
resolution, which makes high and low resolution
systems complementary.
Rapid introduction of digitalization methods
covering digital data recording, telemetering of
data to groundstations and the subsequent data
processing, and (semi) automatic interpretation
techniques. Image enhancement ranks high in this
respect and can be subdivided into digital methods
for restoration of the images through geometric and
radiometric corrections, for contrast improvement
through histogram equalisation, density slicing,
spatial frequency filtering, etc., and for (feature
space) information extraction purposes by way of
automatic classification, maximum likelihood ap
proaches, intensity mapping and ratioing, principal
component transformations, etc.
A cascade of topographic and thematic information
is being constantly poured down over our heads from
satellites and other sources. Since the satellite
remote sensing data are mostly digitized and give
the precise geographical location of the recordings
in X, Y (and Z) coordinates, storing the informa
tion in a data base and its subsequent classifica
tion and retrieval by way of a geographical (or
land) information system (GIS/LIS) has become feas
ible. In the context of planned development, there
is a great need all over the world for rapid data
acquisition and presentation and thus GIS/LIS hold
a good promise for the future.
The resource surveyors have become part of a lar
ger community. As I have already mentioned, several
scientific disciplines that never really were using
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