While air photography evolved into remote sensing, 
the field of photo-interpretation widened to become 
image-interpretation. 
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 
threshold. 
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, 
etc. 
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 
ces. 
MAIN TRENDS 
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 
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