The photographic camera has served as a prime remote sensor for more than 150 years. It captures an image of targets exterior to it by concentrating electromagnetic (EM) radiation (normally, visible light) through a lens onto a recording medium (typically silver-based film). The film displays the target objects in their relative positions by variations in their brightness of gray levels (black and white) or color tones. Although the first, rather primitive photographs were taken as "stills" on the ground, the idea photographing the Earth's surface from above, yielding the so-called aerial photo, emerged in the 1840s with pictures from balloons. By the first World War, cameras mounted on airplanes provided aerial views of fairly large surface areas that were invaluable for military reconnaissance. From then until the early 1960s, the aerial photograph remained the single standard tool for depicting the surface from a vertical or oblique perspective.

Remote sensing above the atmosphere originated early in the space age (both Russian and American programs). At first, by 1946, some V-2 rockets, acquired from Germany after World War II, were launched by the U.S. Army from White Sands, New Mexico, to high altitudes. These were referred to as the Viking program (a named used again for Mars landers). These rockets, while not attaining orbit, contained automated still or movie cameras that took pictures as the vehicle ascended. Here is an example of a typical oblique picture, looking across Arizona and the Gulf of California to the curving Earth horizon (this is shown again in Section 12). (Note: the writer [NMS], as an Army corporal stationed at Fort Bliss in El Paso, TX was assigned as a Post newpaper reporter privileged in Spring 1947 to attend a V-2 launch at White Sands and to interview Werner von Braun, the father of the German V-2 program; little did I know then that I would be heavily involved in America's space program in my career years.)

The first non-photo camera sensors mounted on unmanned spacecraft were aboard satellites devoted mainly to looking at clouds. The first U.S. meteorological satellite, TIROS-1, launched by an Atlas rocket into orbit on April 1, 1960, looked similar to this later TIROS vehicle.

TIROS, for Television Infrared Observation Satellite, used vidicon cameras to scan wide areas at a time. The image below is one of the first (May 9, 1960) returned by TIROS-1 (10 satellites in this series were flown, followed by the TOS and ITOS spacecraft, along with Nimbus, NOAA, GOES and others [see Section 14]. Superimposed on the cloud patterns is a generalized weather map for the region.

Then, in the 1960s as man entered space, cosmonauts and astronauts in space capsules took photos out the window. In time, the space photographers had specific targets and a schedule, although they also have some freedom to snap pictures at targets of opportunity.

 

Sinai Peninsula and Red Sea

Gulf of California & Southern California

(Note: these images, and many others in the Tutorial, have a thin blue border; this means that you can click inside it and it will automatically enlarge to fill most of your screen. To close, try pressing escape, then close, using the X button in the upper right, or on some browsers, just try X first)

During the '60s, the first sophisticated imaging sensors were incorporated in orbiting satellites. At first, these sensors were basic TV cameras that imaged crude, low resolution (little detail) black and white pictures of clouds and Earth's surface, where clear. Resolution is the size of the smallest contrasting object pairs that can be sharply distinguished. Below, we show three examples from the Nimbus satellite's sensors to give an idea of how good the early photos were.

Eastern India, Bangladesh, Himalayas	Saudi Arabia