Having now covered some of the principles behind the nature and use of remote sensing data and methodologies, including sensors and image processing, we switch to a survey of the era of satellite remote sensing (and some mention of aircraft remote sensing and space photography by astronauts/cosmonauts) introduced from an historical framework. Special topics near the end will be multiplatform systems, military surveillance, and remote sensing as it applies to medical imaging systems.
Remote sensing as a technology started with the first photographs in the early nineteenth century (see first page of Overview). To learn about the milestones in remote sensing prior to the first Landsat, look over the next three pages that cover these three areas - Photographic Methods, Non-Photographic Sensor Systems, Space Imaging Systems on the next 3 pages. That review (extracted from the Landsat Tutorial Workbook) ends with events in 1979. You can also find more on the general history of U.S. and foreign space programs in Appendix A and this Wikipedia online Web site. It is also informative to look at Jack Estes' website that surveys the history of aerial photography.
We present major highlights subsequent to 1979 both within this Introduction and throughout the Tutorial. Some of these highlights include short summaries of major space-based programs such as launching several other satellite/sensor systems similar to Landsat; inserting radar systems into space; proliferating weather satellites; orbiting a series of specialized satellites to monitor the environment using, among others, thermal and passive microwave sensors; developing sophisticated hyperspectral sensors; and deploying a variety of sensors to gather imagery and other data on the planets and astronomical bodies.
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. The Daguerrotype plate was the first of this kind. A key advance in photography occurred in 1871 when Dr. Henry Maddox, a Brit, announced development of a photographic negative made by enclosing silver halide suspended in an emulsion mounted on a glass plate (later supplanted by flexible film that is advanced to allow many exposures). Silver halide film remains the prime recording medium today. The film displays the target objects in their relative positions by variations in their brightness of gray levels (black and white) or color tones (using dyes, as discussed in Section 10).
Although the first, rather primitive photographs were taken as "stills" on the ground, the idea of photographing the Earth's surface from above, yielding the so-called aerial photo, emerged in the 1860s with pictures from balloons. The first success - now lost - is a photo of a French Valley made by Felix Tournachon. One of the oldest such photos, of Boston, appears on the first page of the Overview. The first free flight photo mission was carried out by Monsieur Triboulet in 1879. Meanwhile, an alternate approach, mounting cameras on kites, became popular in the last two decades of the 19th Century. E. Archibald of England began this method in 1882. Here is a well-preserved photo (1889) from a kite, snapped by a remote mechanism operated by A. Balut, covering Labrugauere, France:
G.R. Lawrence took several famous kite photos of the devastation in San Francisco, California right after the infamous 1906 earthquake that, together with fire, destroyed most of the city. The best example was shown in the Overview, first page near the top:
It appears that Wilbur Wright - the co-developer of the first aeroplane to leave the ground in free flight - himself was the first to take pictures from an airplane, in France (LeMans) in 1908 and Italy (Centocelli) in 1909.
By the first World War, cameras mounted on airplanes, or more commonly handheld by aviators, provided aerial views of fairly large surface areas that were invaluable for military reconnaissance. This is docmented in these two photos:
From then until the early 1960s, the aerial photograph remained the single standard tool for depicting the surface from a vertical or oblique perspective. More on aerial photography is reviewed on page 10-1.
Historically, the first photos taken from a small rocket, from a height of about 100 meters, were imaged from a rocket designed by Alfred Nobel (of Prize fame) and launched in 1897 over a Swedish landscape; to see this photo, click on the Overview first page.
A camera succeeded in photographing the landscape at a height of 600 meters (2000 ft) reached by Alfred Maul's rocket during a 1904 launch:
Remote sensing above the atmosphere originated at the dawn of the Space Age (both Russian and American programs). The power and capability of launch vehicles was a big factor in determining what remote sensors could be placed as part (or all) of the payload. By 1946 some V-2 rockets, acquired from Germany after World War II, were launched by the U.S. Army from White Sands Proving Grounds, New Mexico, to high altitudes (70 to 100 miles). The first V-2 launch in the U.S. took place in April 17 of 1946. Launch 13 in the V-2 series on October 24, 1946, contained a motion picture camera in its nose cone, which acquired a series of views of the Earth's surface as it proceeded to a 134 km (83 miles) altitude. We show here a photo of one of the White Sands launches of the V-2 (more V-2 pictures are included in an October 1950 article "Seeing the Earth from Space" in the National Geographic).
Here is a motion picture frame from a later V-2 launch that shows the quality of detail in a scene in nearby New Mexico just north of the White Sands launching site:
Smaller sounding rockets, such as the Wac Corporal, and the Viking and Aerobee series, were developed and launched by the military in the late '40s and '50s. These rockets, while not attaining orbit, contained automated still or movie cameras that took pictures as the vehicle ascended. In these early days there were many variants of sounding rockets, along with those being groomed for eventual insertion of objects into orbit. An outdoor display of these at the White Sands Museum is impressive:
Here is an example of a typical oblique picture made during a Viking Flight in 1950, looking across Arizona and the Gulf of California to the curving Earth horizon (this photo is shown again in Section 12).
The White Sands Proving Grounds entered the writer's (NMS) life briefly in 1947. At the time I was in the U.S. Army at Fort Bliss. One of my duties was as a reporter on the Fort Bliss newspaper. I was assigned to cover a V-2 launch at White Sands. There I met Dr. Wernher von Braun and interviewed him (met him again about 40 years later and he remembered that occasion). We watched the launch from a block house and then ran outdoors to see it disappear into the sky. This photo reminds me of the setting at the site:
Now, let us return to satellites that do remote sensing to consider some of the early vehicles. The first non-photo sensors were television cameras mounted on unmanned spacecraft and were 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 first television picture ever from a satellite was this TIROS view:
THIS IMAGE CAN BE NOMINATED AS THE OFFICIAL STARTING MOMENT OF REMOTE SENSING FROM SATELLITES.
Images quickly improved. The image below from May 9, 1960 was also returned by a TIROS spacecraft. Ten 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; this kind of data display soon started to appear in television news broadcasts.
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. (As an aside, Scott Carpenter, the second American to orbit the Earth [after John Glenn], told the writer [NMS] that he became so excited by the views from space outside the capsule window, which he furiously photographed, that he forgot for a moment to flip a switch related to re-entry; as a result, the spacecraft reached the Pacific ocean about 50 miles beyond the planned touch down point. His tourist's enthusiasm earned him a "chewing out".) Here are three early astronaut photos:
Sinai Peninsula and Red Sea
Gulf of California & Southern California
Note: these images, and 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
Early on, other types of sensors were developed that " took images using the EM spectrum beyond the visible, into the near and thermal infrared regions. The field of view (FOV) was broad, usually 100s of kilometers on a side. Such synoptic areas of regional coverage were of great value to the meteorological community, so that many of these early satellites were metsats, dedicated to gathering information on clouds, air temperatures, wind patterns, etc.
We close this page with a subject now in the news rather often, one that is especially a concern during manned missions: the rapid increase in "space junk" which can damage satellites and threaten the International Space Station, the Shuttle and other vehicles carrying astronauts/cosmonautes. These two illustrations zero in on the problem:
The objects shown in the plots are those greater than 10 cm in minimum dimension. The sudden spike in 2007 was due to two events: 1) the destruction in 2007 of a Feng Yun 1C weather satellite by a Chinese missile as an anti-satellite weapons test; and 2) the collision between an active Iridium 33 satellite and an inactive COSMOS 2251 payload. These destructive occurrences validate the growing threats that "space junk" increasingly poses. Since the start of the space program, more than 4600 satellites have been inserted into earth-orbit; about 800 of these are presently still operating. The problem is partially alleviated by deliberately slowing down a satellite so that it falls towards Earth and burns up in the lower atmosphere. A nice summary of the hazards involved can be found at this Wikipedia website.