Considered to be the boundary between Europe and Asia, the Bosporus (Turkish
Bogazici) Strait connects the Black Sea with the Sea of Marmara in northwest Turkey. In
celebration of Earth Day, NASA has released a new shaded relief and radar image of this
geologically complex and historically rich region, taken by NASA’s Shuttle Radar Topography
Mission in February 2000.

The image is available from NASA’s Jet Propulsion Laboratory, Pasadena, Calif., on the
JPL Planetary Photojournal at: .

The Bosporus Strait is depicted in the center of the view. The Black Sea at the top of the
image and Sea of Marmara below the center are colored blue, along with several large lakes.
The largest lake, to the lower right of the Sea of Marmara, is Iznik Lake.

The large city of Istanbul, Turkey is located on both sides of the southern end of the
strait. Its stronger reflection of radar causes it to appear as a brighter (light green to white) area
on the image. Istanbul is the modern name for a city with a long history, previously known as
both Constantinople and Byzantium. In 330 A.D., Constantine rebuilt Istanbul on the site of an
earlier Greek city as the capital of the Roman Empire. It later served as the capital of the
Byzantine and Ottoman empires until 1922.

The narrow Gulf of Izmit extends to the east (right) from the Sea of Marmara. On
August 17, 1999, a magnitude 7.4 earthquake, often called the Izmit or Kocaeli, Turkey
earthquake, heavily damaged the city of Izmit at the end of the gulf and killed at least 17,000
people. A previous earthquake under the Gulf of Izmit in 1754 killed at least 2,000 people. The
Izmit earthquake ruptured a long section of the North Anatolian Fault system from off the right
side of this image continuing under the Gulf of Izmit. Another strand of the North Anatolian
Fault system is visible as a sharp linear feature in the topography south of Iznik Lake. Surveys
measuring water depth in the area show that the North Anatolian Fault system extends beneath
and has formed the Sea of Marmara, in addition to the Gulf of Izmit and Iznik Lake. Scientists
are studying the North Anatolian Fault system closely to determine the risk of future large
earthquakes on the faults close to Istanbul.

Three visualization methods were combined to produce this image: shading and color
coding of topographic height, and radar image intensity. The shade image was derived by
computing topographic slope in the northwest-southeast direction. Northwest-facing slopes
appear dark and southeast-facing slopes appear bright. Color-coding is directly related to
topographic height, with green at the lower elevations, rising through yellow and brown to white
at the highest elevations. The shade image was combined with the radar intensity image to add
detail, especially in the flat areas.

The Shuttle Radar Topography Mission was flown aboard Space Shuttle Endeavour
February 11-22, 2000. It used modified versions of the same instruments that comprised the
Space Shuttle Imaging Radar-C/X-Band Synthetic Aperture Radar that flew twice on Endeavour
in 1994. The mission collected 3-D measurements of Earth’s land surface using radar
interferometry, which compares two radar images taken at slightly different locations to obtain
elevation or surface-change information. To collect the data, engineers added a 60-meter
(approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved
tracking and navigation devices. More information is available at: .

NASA’s Earth Science Enterprise is a long-term research and technology program
designed to examine Earth’s land, oceans, atmosphere, ice and life as a total integrated system.

JPL is a division of the California Institute of Technology in Pasadena.