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
