does imply limits — not absolute limits but limitations imposed by the present state 
of technology and social organization on environmental resources and by the 
ability of the biosphere to absorb the effects of human activities. But technology 
and social organization can both be managed and improved to make way for a 
new era of economic growth." 1 
Achieving the goal of sustainable development is a process which must be managed. In other 
words, if we are to achieve the goal of sustainable development, we must manage our activities 
toward that end. The essential first step in any management process is the acquisition of timely, 
reliable and accurate information. Because the problems of resource and environmental 
management are global, and the planetary systems we are attempting to describe are 
interdependent in as yet ill-understood ways, the information system for global environmental and 
resource management must be capable of encompassing the earth as a whole. This requirement 
points toward space-based measurement of the earth as the basis for such a system. This is not to 
say that such a system would deal only with space-based measurements, it simply means that the 
system would be conceived around the idea of measuring the earth from space as a "backbone" 
concept which serves to define the framework within which all measurements including those 
from non-space sources are processed, stored, accessed and interpreted. Learning to 
understand what all these measurements mean in terms of the trends in the health of the planet 
will be facilitated by imbedding them in a framework which, as an intrinsic characteristic, deals with 
the earth system as a whole. Only when we approach the problem in this way, will we be able to 
objectively understand the trends in the health of the planet's biosphere and the effects we as a 
species are having on that health through our activities. Remote sensing technology, which 
seeks to measure the parameters of planetary systems from a distance, will form the technological 
basis of the required information delivery system. 
MEASURING THE EARTH FROM SPACE 
It is important to emphasize that what we are dealing with here is measurement, not just 
observation. Remote sensing of the earth from space has, since its inception in the early 1970's, 
been regarded largely as an exercise in "picture taking". We have produced and visually 
interpreted magnificent pictures of the earth’s surface and its atmosphere from spaceborne 
platforms. The instruments which we fly in space are however capable of far more than simple 
observation. They are precise measuring instruments which can be calibrated both spatially and 
radiometrically to high accuracy. This capability is necessary to be able to monitor trends over time 
in an objective way. It allows us to quantify changes in the earth's system which can be related to 
physical processes in an objective and quantifiable way. Being able to deal with the data in this 
way is essential to being able to utilize spaceborne data successfully as inputs to earth system 
models. The use of these models will be fundamental in gaining the understanding necessary for 
the successful management of the resources and environment of our planet in the long term. 
From the point of view of spaceborne measurement, the earth can be thought of as having four 
major components: the land, the ocean, the atmosphere, and the icecaps. When sensing these 
various components, it must be remembered that they are all interrelated. One cannot consider 
the atmosphere independently of the ocean or the land, and one certainly cannot sense the land 
without taking into account the effects of the atmosphere through which it must be observed. For 
example, to one who is concerned with tracking atmospheric phenomena, the effects of the 
atmosphere on the observed radiation contains information (i.e. it is "signal"), while one who is 
interested in tracking phenomena on the surface, such as ocean surface temperature for 
example, would regard the effects of the atmosphere on the radiation as an interfering signal or 
"noise". An information system put in place to objectively monitor the planet must be capable of 
satisfying the needs imposed by many diverse requirements such as these. 
1 World Commission on Environment and Development, Our Common Future Oxford University Press 
1987, page 8. 1