Green Circles—Al Khufrah Oasis, Libya
Green circles in the desert frequently indicate tracts of agriculture supported by center-pivot irrigation. The Al Khufrah Oasis in southeastern Libya (near the Egyptian border) is one of Libya’s largest agricultural projects, and is an easy-to-recognize landmark for orbiting astronauts aboard the International Space Station. Because only about 2 percent of Libya’s land receives enough rainfall to be cultivated, this project uses fossil water from a large underground aquifer. The Libyan government also has a plan called the Great Man Made River to pump and transport these groundwater reserves to the coast to support Libya’s growing population and industrial development.
The center-pivot irrigation system pumps water under pressure into a gantry or tubular arm from a central source. Anchored by a central pivot, the gantry slowly rotates over the area to be irrigated, thereby producing the circular patterns. Although the field diameters vary, these fields are approximately 0.6 mile (1 kilometer) in diameter. Darker colors indicate fields where such crops as wheat and alfalfa are grown. Lighter colors can indicate a variety of agricultural processes: fields that have been harvested recently; fields that are lying fallow; fields that have just been planted; or fields that have been taken out of production.
Astronaut photograph ISS010-E-5266 was acquired October 28, 2004 with a Kodak 760C digital camera with a 180 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.
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