Astronaut Photography - Observing Earth's Systems from Space
by Rebecca Dodge in collaboration with NASA scientists
Earth System Science focuses on the interconnections among processes taking place in the Earth's atmosphere, hydrosphere, lithosphere, and biosphere Systems. Multiple processes within the Earth System are being observed and studied from Earth's orbit. Astronaut photographers on the International Space Station are photographing the Earth every day, collecting valuable observations that continue a lengthy tradition.
This classic photograph 1 of the Earth was taken on December 7, 1972; the original caption is below:
"View of the Earth as seen by the Apollo 17 crew traveling toward the moon. This translunar coast photograph extends from the Mediterranean Sea area to the Antarctica south polar ice cap. This is the first time the Apollo trajectory made it possible to photograph the south polar ice cap. Note the heavy cloud cover in the Southern Hemisphere. Almost the entire coastline of Africa is clearly visible. The Arabian Peninsula can be seen at the northeastern edge of Africa. The large island off the coast of Africa is the Malagasy Republic. The Asian mainland is on the horizon toward the northeast."
1. (http://eol.jsc.nasa.gov/EarthObservatory/The_Blue_Marble_from_Apollo_17.htm) The Blue Marble from Apollo 17
The classical Geographer's perspective is evident in the caption, with a focus on location. Earth System Science analyses such photographs from the perspective of the connections among the Earth's four spheres. A few of the Earth's Systems expressed in this single photograph include:
Atmosphere: The intertropical convergence zone (ITCZ) is highlighted over the Indian Ocean north of Madagascar by a narrow band of clouds, which broadens over the African continent. The cloud cover nearly masks the deep green signature of the tropical rain forest, which peeks out to the north of the cloud cover in this December scene when the ITCZ has moved south during the Southern Hemisphere "summer". Coastal Mountains on the eastern edge of Madagascar force moist Pacific air upwards, generating a band of clouds parallel to the mountains (orographic lifting). The deserts of northern and southern Africa and Saudi Arabia lie beneath the subtropical high-pressure cells - the deserts in these regions form beneath descending dry, warm air and appear as brown, unvegetated expanses.
Lithosphere: Towards to top of the photograph the African continent has separated from the Arabian Peninsula along a tectonic rift zone that has created the Red Sea. An earlier rifting event completely separated Madagascar from Africa. Directly east of Madagascar the volcanic islands of Reunion and Mauritius exemplify "hot spot" volcanoes formed over mantle plumes beneath the Earth's oceanic crust. Along the northern edge of the continent of Africa parallel ridges represent folded mountains formed in an earlier collisional event between Africa and Europe, which created the Atlas Mountains of North Africa.
Hydrosphere: The vast expanses of ocean in the Southern Hemisphere are broadly evident in the photograph. This tremendous accumulation of ice - the planet's largest repository of fresh water, covers the continent of Antarctica in a white pall thousands of meters thick. Lake Chad, which lies just north of the tropics, spans 2 degrees of latitude (similar in size to the Great Salt Lake, U.S.). The lake has been fed for thousands of years by streams sourced in the rain forest to the south.
Biosphere: The center of the continent of Africa, although partially covered by clouds, shows a vast green swath of rain forest. The most diverse ecosystem on the planet is supported by heavy rainfall related to the ITCZ, which migrates north and south across this swath with the seasons. Vegetation cover on Madagascar is densest (greenest) on the eastern edge of the island, on the windward side of the coastal mountains, and decreases towards the west in the rain shadow of the mountain.
Based on astronaut photographs such as this, scientists of all kinds soon saw the promise of Earth Observations from orbit and demanded more. Earth Observations photography became an ongoing part of the Space Program, and led to the development and launch of automated Earth Observation Satellites. However, the human touch is still critical to the observation and monitoring of the Earth's systems, as proven by the continuing successful applications of photographs taken by Space Shuttle astronauts. On the International Space Station (ISS) installation of the Destiny Module sets the stage for exciting new observation opportunities. The photograph2 to the left shows the location of a special observation window equipped with highest-quality optical glass, to facilitate earth observations performed by astronauts with hand-held cameras.
2.(http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4691 The International Space Station's New Destiny Module)
The window, shown to the right, is suitable for nadir (observing vertically downwards) and oblique (observing at an angle to the ground surface) photography3.
3. (http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=4696 Window Observational Research Facility)