The need to effectively monitor our resources and measure the impact of events on our environment is becoming increasingly important. We now realise that some events that take place half a world away can and do affect us and we appreciate that timely information has always been a powerful and vital part of decision making. I put it to you that in managing the precious resources of our world for future generations, accurate information has never been more essential.

For some years now, the science (and sometimes art) of remote sensing has been recognized as a valuable tool for monitoring the Earth's natural resources. The definition of remote sensing has been described as the means of sensing or measuring things (objects, areas or phenomena) without coming into direct contact with the phenomenon. An important question, therefore, is - what exactly is measured? - the emitted, scattered and reflected electromagnetic energy from the phenomena under investigation. From these measurements, useful information is then extracted through visual or computer-assisted interpretation. Satellite data, in particular, can provide relatively inexpensive, repetitive datasets that can either augment or replace expensive and often time consuming ground based monitoring programs. They provide an instantaneous view of surface phenomena over large areas that are often inaccessible to ground personnel due to physical or political reasons.