Civil Land Observation Satellites

Abstract The first, and still the most dramatic, example of seeing where we live from the vantage point of space was the image of a pale blue and white globe hanging all alone in an infinite expanse of darkness taken through the window of Apollo 8 on its way to the Moon in December 1968. Three and a half years later on 23 July 1972, NASA launched ERTS‐1, later renamed Landsat‐1. This was the first civil imaging satellite that had enough resolution, 80 meters, to image human‐scale activities, that is, everything bigger than a football field. Its more capable successors now provide anyone, anywhere, the ability to see images of motorcycle size objects any place on the globe at almost any time. As of November 2002, there are 19 satellites in orbit whose resolutions range from 30 meters down to 0.6 meter. (The number of systems in orbit is somewhat volatile; four are old and may fail by the time this article is published, and five more are likely to be launched during that same period.) They are being operated by the United States, France, India, Korea, Canada, China/Brazil, the European Space Agency, and three private corporations, two U.S. and one Israeli. The number of satellites and the number of their national and private sponsors show that civil land observation satellites have arrived at the point where they are now another permanent payoff of the space age. It will take much longer than the Weather, Communication and Global Positioning System (GPS) satellites for their full economic and social effects to be felt, but they are already forcing national and international discussions on the effects on nations, corporations, and individuals of the worldwide transparency that these satellites will inevitably bring. This article discusses the special set of Earth orbiting satellites designed to acquire detailed images of the global land surface. It is the high‐resolution subset of the larger family of Earth sensing satellites that image the land and oceans on a kilometer scale and measure the characteristics of the atmosphere to record the weather and to explore the complex interrelationships among the atmosphere, the oceans, and the land surface that cause the weather and our climate. The satellite, sensor, and data technologies involved are described. The landsat history is detailed. Programs of the international period are included. The possibilities of using radar in civilean satellites is discussed.