Orbital remote sensing of the Earth´s surface: a review

Summary form only given. This paper reviews the early years of remote sensing of the earth´s surface, as distinguished from its atmosphere, and shows the influence of manned space flight, in particular the Apollo Program. The first orbital-altitude pictures of the earth were taken from sounding rockets in the 1950s, and eventually led to terrain photography by astronauts of the Mercury, Gemini, and Apollo Programs using hand-held 70 mm cameras. There was virtually no appreciation of the scientific value of such photography before the Mercury and Gemini missions. However, the hundreds of high-quality color pictures from these missions triggered a surge of interest among earth scientists. In particular, the Gemini and Apollo earth-orbital photographs stimulated the U.S. Geological Survey to propose an earth resources satellite, which eventually became Landsat with the first launch in 1972. Landsat can thus be considered a by-product of the Apollo Program. Its success led to many subsequent observation satellites, launched by France, the former Soviet Union, India, and China. The limitations of visual range imagery-daylight availability and cloud cover-led to development of imaging radar satellites, beginning with Seasat in 1978. Since then, orbital radar as typified by ERS-1 and 2, and most recently RADARSAT, has become an invaluable remote sensing tool, both for imaging and for radar interferometry of crustal motions