James S. Aber
|Early photography||Shuttle photography|
Systematic manned space photography was undertaken during the Skylab missions of 1973 and 1974. Skylab was a orbiting space station that was utilized for extended Earth observations (Wilmarth et al. 1977). The overall objectives were to determine the quality and quantity of photographic and observational data that could be collected by astronauts with benefit from preflight training and ground support during flight.
|It was recognized that astronauts needed much additional preflight scientific and operational training to take multidisciplinary photographs (Wilmarth et al. 1977). Skylab 4 was most successful; about 2000 photographs were obtained of more than 850 features and phenomena. The lessons learned during Skylab missions formed the basis for the program of space-shuttle photography in the 1980s and 1990s.|
|Near vertical||View straight down to Earth's surface|
|Low oblique||View toward side—horizon not visible|
|High oblique||View toward side—horizon visible|
Space-shuttle photography was the result of systematic Earth and environmental science training given to each astronaut crew prior to flight. Much of the photography consisted of revisits to targets previously photographed. Each day during flight, astronauts were given instructions for photographs based on cloud-cover and orbital conditions. Astronauts were also free to take photographs of any interesting or attractive scenes. Special advantages of astronaut photography include (Lulla et al. 1993) the following.
|Color visible||Normal color film sensitive to|
blue, green and red light.
|Color infrared||Color-IR film sensitive to green, red, and near-infrared energy.|
The electronic still camera (ESC) is a charged-couple device (CCD) that produces near-film-quality images in digital format. It was introduced for space-shuttle missions in 1991. It had a spectral response range of 0.4 to 1.1 µm, which was significantly greater than films then in use. Since then, digital cameras have become the norm in the twenty-first century.
The ground coverage of space-shuttle photography was determined by factors of orbit geometry that varied with each mission. The most important factor was orbit inclination, ±28.5°, for most space-shuttle missions, which limited photographs to low-latitude locations. This includes about one-half of the Earth's surface, an area with more than 75% of the world's human population. Orbital inclinations from ±34.3° to a maximum of ±57° were used on some special missions. For the latter, regions up to around ±60° latitude could be photographed in low-oblique views. High-latitude areas above the Arctic and Antarctic circles were photographed only rarely in high-oblique views.
Time of launch and crew sleeping schedules affected the times of daylight when photographs could be acquired, as few pictures were taken on the Earth's night side. Thus, some missions returned pictures mainly from the northern hemisphere, whereas other missions took photos mostly in the southern hemisphere. An important factor is cloud cover that often obscures ground features of interest. For example, many sites have few or no cloud-free photographs. Photography was not the primary objective on most space-shuttle flights, so pictures were taken when astronauts were not busy with other duties. The result of these factors is uneven coverage of the world by manned-space photography.
Space-shuttle photography has been utilized for several global-change studies (Lulla et al. 1991). These include monitoring of inland water bodies in climatically sensitive areas, for instance the Great Salt Lake, Aral Sea, Lake Chad, etc. Photographs have also been used to document changes in deltaic and estuarine environments, for example the Omo delta of Lake Turkana. Space-shuttle photographs are also valuable for studies of ephemeral events, such as volcanic eruptions, auroras, and dust storms. Color-infrared photographs are useful for establishing biomass (vegetation).
Smoke from natural or man-made fires is a feature of special interest. Compared to other forms of space-based remote sensing, space-shuttle photography excels for imaging smoke from burning biomass (Glasser and Lulla 1998). Space-shuttle photography proved especially valuable for monitoring oil-field fires during the Kuwait War (Lulla and Helfert 1991). Pictures were acquired during two shuttle missions in April and May of 1991. The presence of human photographers in space has demonstrated some important capabilities to:
International Space Station
During the period 1995-98, Shuttle/Mir missions paved the way for development of a permanently manned space station. Known as International Space Station, Phase 1, more than 20,000 new photographs were acquired during these missions (Glasser and Lulla 1998). The International Space Station became operational early in the twenty-first century. It includes a nadir window dedicated to Earth observation experiments. It facilitates high-quality remote sensing in the visible, near-infrared, and mid-infrared portions of the spectrum. Equipment racks around the window provides support, power, and communciations for various kinds of cameras and sensors. The space station also has external mounts for securing remote sensing devices outside the hull.
Continuous, long-term operation of the space station provides unparalleled opportunity for Earth observation. The space station orbits at inclination ±51.6°, which covers more than 75% of the Earth's surface, containing 95% of the human population. Beneath this orbit, every ground locality is revisited each three days, which increases the chances for cloud-free imagery. Earth-observation experiments are now underway, and many kinds of scientific missions are anticipated (Lulla, pers. com.).
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