ABSTRACT
Solar radiation reaches the outer limit of the Earth's atmosphere virtually undepleted except for the effect of distance. Since the total radiation from a spherical source, such as the Sun, passes through successively larger spheres as it radiates outward, the amount passing through a unit area is inversely proportional to the square of the distance between the area and the radiation source. Although the Earth, 93 million miles from the Sun, intercepts less than one 50-millionth of the Sun's total energy output, this intercepted energy is vital not only to many remote sensing techniques (either directly or indirectly) but also to terrestrial life itself.
