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Astronaut Photography of Earth - Display Record
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IdentificationMission: ISS030 Roll: E Frame: 59398 Mission ID on the Film or image: ISS030
Country or Geographic Name: CHAD
Features: LAKE FITRI, DUNES, NGELO, NESSABA
Center Point: Latitude: 12.8 Longitude: 17.5 (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: 21
Camera Focal Length: 180mm
Camera: N2: Nikon D2Xs
Film: 4288E : 4288 x 2848 pixel CMOS sensor, RGBG imager color filter.
Percentage of Cloud Cover: 10 (0-10)
GMT Date: 20120119 (YYYYMMDD) GMT Time: 121955 (HHMMSS)
Nadir Point Latitude: 13.8, Longitude: 18.5 (Negative numbers indicate south for latitude and west for longitude)
Nadir to Photo Center Direction: Southwest
Sun Azimuth: 211 (Clockwise angle in degrees from north to the sun measured at the nadir point)
Spacecraft Altitude: 216 nautical miles (400 km)
Sun Elevation Angle: 50 (Angle in degrees between the horizon and the sun, measured at the nadir point)
CaptionsLake Fitri, Chad
Lake Fitri is an endorheic, or terminal lake in a desert basin in the southern Sahara Desert. Muddy yellow-brown water marks the center of the depression (image center), with a ring of dark brown muds and burnt vegetation on the exposed lake floor to the north. The lake shoreline supports a thin line of reed and floating grass vegetation which appears as dark green in the image. Deserts have so little rainfall that many rivers cannot reach the sea, but end at local low points where they form lakes. Here the usually dry Wadi Batha empties into Lake Fitri. Over time, water flow in Wadi Batha has created a large delta, which occupies the entire top left third of the image—a sense of scale is given by the 23–km length of the lake. The lake has been designated under the Ramsar Convention as a wetland of international importance.
Other features visible in the image reveal evidence of significant climate change. The dry part of the present lake shows that the lake has been larger in the last several decades. But the lake was once many times larger than its present surface area, as shown by numerous sweeping curves of ancient beaches which are now situated many kilometers from the present shoreline, at higher altitudes (image upper right). Inland lakes are highly sensitive to the exact equilibrium between the amount of inflow from contributing rivers like Wadi Batha and evaporation. Each beach ridge therefore shows a different lake level and thus a different balance in the lake-river-climate system. A smaller river enters from the south (top right) and cuts through the beach reaches on its way to the lake.
The irregular, elongated, tan patches to the west of the lake are linear dunes aligned parallel to the dominant winds which blow from the northeast. The dunes have all formed on the downwind side (southwest) side of the lake since the lake bed and delta provide the sands which have built the dunes. The dunes indicate that during past climatic phases the lake has been almost or completely dry on repeated occasions—often enough for these great dunes, many kilometers long and several meters high, to form even in the lowest parts of the lake. The islands visible in the center of the lake are likewise remnants of dunes. These dunes are smaller than those on the lake margin, presumably because waves from the lake have eroded them. Villages occupy the points of some major dunes, and some islands, where fishermen can gain easy access to the lake.
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