To Glenys, Sandie, and Liza
The Earth's atmosphere is a puzzle and a concern. Its unpredictable weather has always been a force to be reckoned with, but until recent times, our trust was implicit in the robustness of the atmospheric system as the foundation of our biosphere. Now we are not so sure. Far from being robust, this system is better described as a balance among a number of natural forces that we barely understand. Our concern is deepened when we consider the threat to this balance from our burgeoning civilization and its effluents. What, for example, are the chlorofluorocarbons doing to the ozone layer, and how significantly and on what time scales will the increasing CO2 production change the climate? There will be no answers to such questions without a strong and steady program of research to understand fundamental atmospheric processes. Essential to this is the gathering of basic data such as temperature, pressure, wind, and the distribution of water vapor, clouds, and other active constituents. Such data enable us to test existing models for the atmosphere's energy balance, the depletion of the ozone layer, the hydrological cycle, climate trends, and other aspects of the atmospheric system that are of vital interest to us, and to formulate new and better models to guide us in the future. Remote sensing is central to this effort because it is the only way we can obtain the full spatial and temporal perspective needed to understand atmospheric processes. The strong conclusion is that the need for remote sensing will continue, and grow.