Remote Sensing from Satellites

In 1858, less than two decades after the invention of daguerrotype photography, a photograph of Paris was taken from a balloon. This event is generally recognized as the first demonstration of “remote sensing.” The use of aerial photography was attempted soon afterward during the Civil War in the United States, and this effort demonstrated that balloons were both useful observational platforms and easily recognizable targets. Photographs from balloons at higher altitude, kites, airplanes, and even pigeons were acquired in subsequent years, with an emphasis on military applications, particularly during the two world wars. The idea of photographing the earth from space, however, was apparently first described for nonmilitary applications by Dr. Harry Wexler at a symposium held at the Hayden Planetarium in New York in 1954. Dr. Wexler included a sketch of what a satellite camera 4000 miles over Texas might observe. In 1957 (the International Geophysical Year), President Dwight Eisenhower announced Project Vanguard, which would orbit several earth-observing satellites. Although numerous Vanguard launches failed, Vanguard 2, launched on February 17, 1959, carried a cloud-cover observation experiment, but satellite wobble prevented the acquisition of useful imagery. The first U.S. satellite, Explorer 1, which launched on January 31, 1958, carried Geiger counters provided by Dr. James Van Allen. The Geiger counter data indicated the existence of the Van Allen radiation belts, the first geophysical discovery made by satellites. Vanguard mission SLV-6, launched on June 22, 1959, carried a radiation balance experiment created by Verner Suomi, but the mission failed to reach orbit. However, Explorer VII, launched on October 13, 1959, carried a similar experiment, and this mission provided the first measurement of the solar constant and the first longwave radiation budget map of the earth.