Satellite data are objective. Satellite data are acquired, transmitted and archived by machines. No human editing, biasing or censorship is involved in the data acquisition stage. Each pixel is an objective measurement of the condition of the surface of the Earth. The data coding the relative brightness in each waveband for each pixel are collected systematically in space as well as in time with a census sample; ie. complete coverage of the surface of the Earth. It is only in the final stage of interpretation that subjective interpretation occurs. That presents no problems. If you and I disagree about the interpretation of a satellite image in this book, that is healthy and good for science. We can differ only about our interpretation and not about the data. The data that we both use, the image, remain the same. Satellite data are objectively acquired and there are enormous volumes of it. Within the national satellite archives in Canberra, there are approximately 250 Landsat MSS images of every pixel of the Australian continent since mid-1972.
There is a very great contrast between the systematic, objective measurement systems onboard satellites and the assessment and monitoring of our environment that people do. Our assessment is subjective rather than objective and it is based on a very small sample in comparison with the complete 'wall-to-wall' coverage of satellite imaging systems. The greatest disparity is in the way in which we humans monitor the world around us compared with what can be achieved using satellite data. Our archive of what the world was like is our memory. Our memory, our operational archive, is, unfortunately seriously flawed in its creation and fallible in its retrieval. We selectively remember things in the first instance and then do not always recall all relevant information. As an archive, we are biased and forgetful. These failings shape our lives because we are what we remember. That is the nature of human beings; a nature that is the product of the way we have evolved during the last million years or so.
It is a characteristic of our behaviour to react to rapid or episodic change in preference to slow and monotonous change. It's far easier to occupy ourselves with the daily micro-hassles of life than with changes occurring over the longer term. Our social, political and economic lives are dominated by the now rather than the critically important future. This domination is largely dictated by our media that, with words, images and skill, force our concentration on daily trivia, eg. a knee operation for a football player, while completely ignoring the long term changes, such as the relentless increase in the atmospheric concentration of chlorofluorocarbons (CFCs) and greenhouse gases.
Now, bearing all of these points in mind, we can ask a simple yet important question: If you wanted to discover what was really happening to your world, which archive would you tap? Would you use the collective human memory? This archive we know to be familiar but neither objective, complete or systematically updated. Or would you rather access a database that has it all there? A database of objective measurements, not subjective impressions, that was made systematically in space and in time?