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: http://www.naic.edu/~pradar/asteroids/2007TU24/
Дата изменения: Thu Jan 31 03:21:24 2008 Дата индексирования: Tue Aug 18 03:14:41 2009 Кодировка: Поисковые слова: m 8 |
This radar image of 2007 TU24 was obtained on January 28, 2008, about 12 hours before the asteroid's 1.4-lunar-distance pass by the Earth, from an observation that used the Arecibo telescope to transmit a 300-kilowatt beam of radio energy toward the asteroid and the Robert C. Byrd Green Bank Telescope, (GBT) in West Virginia to receive the echoes. The image summed echoes recorded over about three minutes. The intrinsic resolution of the image is about eight meters (25 feet). Distance from the Earth increases from top to bottom. Unlike normal optical images, radar images show how echo power is distributed in range, or distance from the viewer, and Doppler frequency, which is proportional to how fast a resolution cell is moving toward or away from the viewer: In this image, speed toward the Earth increases from left to right. Despite the unusual radar imaging geometry, the image reveals important characteristics of this object. Its visible extent is about 100 meters, and since typically about half of an object is concealed from our view, the object's overall extent probably is around 200 meters. The object also is clearly at least slightly asymmetrical, and also show evidence for nonuniform, probably nonconvex topography. Images with similar resolution obtained on Jan. 28 and during observations planned for Feb. 1-4 should show other orientations of the object, and may permit estimation of its three-dimensional shape. This experiment produced 8-meter-resolution images of a 0.2-km asteroid when it was about 540,000 km away. This is like using a camera in New York to image a person in Los Angeles with several-inch resolution.