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The Gateway to Astronaut Photography of Earth
(NASA Crew Earth Observations)
Astronaut Photography of Earth - Display Record
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IdentificationMission: ISS022 Roll: E Frame: 5258 Mission ID on the Film or image: ISS022
Country or Geographic Name: NIGER
Features: SAND DUNES, TENERE DESERT, ERG OF BILMA
Center Point Latitude: 17.2 Center Point Longitude: 11.5 (Negative numbers indicate south for latitude and west for longitude)
Stereo: (Yes indicates there is an adjacent picture of the same area)
ONC Map ID: JNC Map ID:
CameraCamera Tilt: 40
Camera Focal Length: 400mm
Camera: N2: Nikon D2Xs
Film: 4288E : 4288 x 2848 pixel CMOS sensor, RGBG imager color filter.
Percentage of Cloud Cover: 10 (0-10)
NadirGMT Date: 20091201 (YYYYMMDD) GMT Time: 064436 (HHMMSS)
Nadir Point Latitude: 15.7, Longitude: 9.5 (Negative numbers indicate south for latitude and west for longitude)
Nadir to Photo Center Direction: Northeast
Sun Azimuth: 118 (Clockwise angle in degrees from north to the sun measured at the nadir point)
Spacecraft Altitude: 181 nautical miles (335 km)
Sun Elevation Angle: 15 (Angle in degrees between the horizon and the sun, measured at the nadir point)
Orbit Number: 3228
CaptionsSand Dunes in the Tenéré Desert, Niger
This detailed astronaut photograph highlights sand dunes in the Fachi-Bilma erg (sand sea) in the central-eastern part of the Tenéré Desert. The Tenéré occupies much of southeastern Niger and is considered to be part of the larger Sahara Desert, which stretches across northern Africa. Much of the Sahara is comprised of ergs; with an area of approximately 150,000 square kilometers (57,915 square miles), the Fachi-Bilma is one of the larger sand seas.
Two major types of dunes are visible in the image. Large, roughly north-south oriented transverse dunes fill the image frame. This type of dune tends to form at roughly right angles to the dominant, northeasterly winds. The dune crests are marked in this image by darker, steeper sand accumulations that cast shadows. The lighter-toned zones between are lower, interdune “flats.” The large dunes appear to be highly symmetrical with regard to their crests. This pattern suggests that the crest sediments are coarser, preventing the formation of a steeper slip face on the downwind side of the dune by wind-driven motion of similarly sized sand grains.
This particular form of transverse dune is known as a zibar, and it is thought to form by winnowing of smaller sand grains by the wind, which leaves the coarser grains to form dune crests. A second set of thin linear dunes oriented at roughly right angles to the zibar dunes appears to be formed on the larger landforms and is therefore a younger landscape feature. These dunes appear to be forming from finer grains in the same wind field as the larger zibars.
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Recommended Citation: Image Science and Analysis Laboratory, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth." .