lagery as a coun- 
high-resolution, 
Is fully realised 
n made no mention 
al remote sensing 
is imagery is now 
r of planets and 
sf other planets, 
^ientific imagin- 
rticipants while 
(too) low assess- 
mineral) resour- 
of the last few 
te following main 
:s that has freed 
row visible spec- 
ig in all usable 
lectrum from the 
nfrared zone and 
r iolet. 
srding altitudes 
¡xtra-terrestrial 
titude of 36,000 
) satellites and 
00 km for orbit- 
.ites to 250-300 
ximately 18,000- 
t include super- 
onal, low-flying 
s. 
relatively short 
he possibilities 
rial photographs 
usually years or 
biting resource 
olution of less 
cloud cover in- 
tationary satel- 
t (interval of a 
course, a trade- 
on and temporal 
low resolution 
Lzation methods 
telemetering of 
subsequent data 
interpretation 
:s high in this 
digital methods 
jh geometric and 
ast improvement 
ensity slicing, 
and for (feature 
oses by way of 
likelihood ap- 
Loing, principal 
itic information 
r our heads from 
e the satellite 
itized and give 
: the recordings 
ng the informa 
ient classifica- 
eographical (or 
îas become feas- 
r elopment, there 
for rapid data 
us GIS/LIS hold 
¡ part of a lar- 
tioned, several 
¡ally were using 
ogy and oceano- 
graphy, have developed a great interest in satellite 
remote sensing, particularly in low resolution ima 
gery. The field of application of aerospace data for 
resource development and related subjects thus has 
grown substantially. This, however, is only one and 
even relatively minor aspect of the matter. Resource 
surveyors share their interest in aerospace techno 
logy with photogrammetrists, making and updating 
topographic maps, with geodesists and geophysicists 
measuring the shape of the Earth and with astron 
omers exploring our planetary system and even the 
universe. The breakthrough of space technology has 
the effect of rapidly pushing forward the frontiers 
of science! In fact, although nowadays entire satel 
lite systems are devoted to resource studies of our 
planet, very substantial sums are spent on other, 
quite different, aspects of space research (telecom 
munications for example). Cynical people will say 
that governments do not usually spend such vast 
amounts of money for the sake of pure science and 
that the military potentials of rockets and space 
craft are the reasons behind it. These potentials 
undeniably exist but need not worry us unduly as 
resource surveyors. There is, in fact, nothing new 
in this respect: aircraft development has in the 
past hardly been influenced by considerations of 
resource surveying, but through the years photogram 
metrists and photo-interpreters alike have neverthe 
less greatly benefitted from it. Also, I feel that 
the military potentials are just a part —and prob 
ably not even the most crucial part—of the engine 
pushing space research. A space-industrial complex 
is developing and technologic breakthroughs in 
fields such as super computers and micro-chips are 
triggered. We are moving quickly to the post-indus 
trial space era with its inherent problems related 
to advanced technology, economic growth, employment, 
utilization of human resources, social discrepancies 
between various parts of the globe, preservation of 
our cultural heritage, etc. We resource surveyors 
nowadays are like the small sucker fish that is 
attached to the skin of a whale (or shark), while 
being thrust forward by the whale of space technol 
ogy, we —living in symbiosis with it— have to find 
applications that are justifiable from an economic, 
scientific and social point of view. 
THE CHANGING FACE OF RESOURCE SURVEYING FOR 
DEVELOPMENT 
The rise of aerospace technology has affected re 
source surveying in various ways by making images of 
different types and scales available. Nevertheless, 
the same basic methods of image interpretation still 
apply throughout, —the essence of which is indi 
cated in Fig. 1. An eye-brain interactive system 
based on visible image density (greytone, colour) 
and relief elements leads to an assessment of the 
(usually) invisible resources, through a reiterative 
process of observation deduction, induction and 
verification that generates hypotheses, interpre 
tations and conclusions. Obviously, technologically 
perfected data acquisition and scientifically well- 
trained interpreters are of equal importance for 
obtaining optimum results, in much the same way as 
refined equipment and a skilled watchmaker are re 
quired to produce a good watch. 
The density can be pictured in grey tones or in 
colours and relates specifically to the vegetal 
cover, to surface water, ice and snow and to barren 
soil or rock. The relief can best be pictured 
stereoscopically, although also monoscopically some 
data can be obtained through shadow (density) pat 
terns. It is particularly important as an indicator 
of terrain forms. While in stereoscopic photo-inter 
pretation both density and relief criteria played a 
rather balanced part, the development of airborne 
satellite remote sensing during the last decades has 
strongly enphasised the analysis of density pat 
Figure 1. The reiterative process of eye-brain 
interaction in image interpretation. 
terns. Image interpretation, especially in the 
fields of the "green" and "blue" sciences (vegeta 
tion, land use, surface hydrology, oceanography), 
has benefitted from this. Although "brown" (earth) 
sciences have also been positively affected by 
improved density analysis, a stronger impetus for 
them can be expected in the years to come: With the 
advent of SPOT and also metric camera/large format 
camera, etc., stereoscopic relief has been intro 
duced as a criterion in the interpretation of or 
bital imagery. 
When briefly outlining the increased capacity of 
image interpretation the following picture emerg 
es: 
Multi-spectral recordings have considerably im 
proved both qualitative and quantitative image 
interpretation methods. The possibilities for re 
cognition and identification of objects by visual, 
qualitative means have increased distinctly but the 
scope in the context of quantitative studies of 
spectral signatures and digital data processing is 
enormous. Quantitative relief analysis using satel 
lite remote sensing is as yet much less advanced 
and is a promising area of research now that 
stereoscopic satellite imagery has come on the 
market. 
Multi-temporal recordings have given new impetus 
to the field of dynamic image interpretation. It 
may relate to monitoring of daily/hourly changes in 
cloud patterns, of seasonal changes in vegetation 
patterns, of sea water temperatures and of sudden 
or gradual changes in the land surface, such as 
coastlines and river courses. The requirements for 
spatial and temporal resolution vary with the type 
of phenomenon concerned and the affected surface 
area. Generally there is a trade-off between low- 
resolution images/data obtained at short intervals 
and high-resolution images taken at larger inter 
vals. In this respect, there is ample scope for 
both high and low-resolution satellite data. A 
special case is the monitoring of sudden and often 
catastrophic natural disasters, such as floods. 
Time-specific recordings are then required and the 
present problem is that low-resolution data are 
inadequate and high-resolution imagery from orbit 
ing satellites may not be available either because 
there is no pass at the required time or because of 
cloud cover. More frequent satellite passes and/or 
all-weather (radar) systems are thus badly needed. 
An often insufficiently understood characteristic 
of disaster surveying using satellite imagery as a 
tool is that the hazard zoning usually has to be 
established in advance on the basis of the terrain 
configuration visualized on earlier, pre-disaster, 
images which are then to be matched with the time- 
critical images taken during the disaster. 
Multi-phase recording has been advocated 
as a