FIGURE 4.1 Arecibo radar images of the 2-kilometer-diameter near-Earth asteroid 1992 UY4 from 4 days of data obtained in August 2005. Illumination is from the top; range increases downward, and the wavelength of the echoes of the radio waves increases to the left; the Doppler frequency shift due to rotation affects the left-right positions of pixels. The resolution of each image is about 7.5 meters in each direction. The images reveal that 1992 UY4 is about 2 kilometers in diameter, with a rounded, slightly asymmetric shape, and that it has numerous topographic features. SOURCE: Courtesy of L.A.M. Benner, NASA, JPL.

FIGURE 4.1 Arecibo radar images of the 2-kilometer-diameter near-Earth asteroid 1992 UY4 from 4 days of data obtained in August 2005. Illumination is from the top; range increases downward, and the wavelength of the echoes of the radio waves increases to the left; the Doppler frequency shift due to rotation affects the left-right positions of pixels. The resolution of each image is about 7.5 meters in each direction. The images reveal that 1992 UY4 is about 2 kilometers in diameter, with a rounded, slightly asymmetric shape, and that it has numerous topographic features. SOURCE: Courtesy of L.A.M. Benner, NASA, JPL.

exceeded only by rendezvous spacecraft missions. Because of its greater sensitivity, Arecibo provides significantly more frequent opportunities for high-resolution imaging than does Goldstone. Opportunities for radar imaging with a caliber comparable to those shown here occur several times annually. Within its latitude coverage, Arecibo can detect objects at twice the distance as can Goldstone for similarly sized objects and has contributed two-thirds of all radar range and radial velocity measurements on NEOs obtained in the last decade.

Observing time at Arecibo is awarded on a competitive basis from proposals that are normally submitted quarterly. Arecibo is also available for “urgent” target-of-opportunity observations on short notice and, in a small number of instances, has been used for radar observations of NEOs within 24 hours of their discovery.

Goldstone Solar System Radar

The Goldstone Solar System Radar, located in the Mojave Desert in southern California, is part of NASA’s Deep Space Network (DSN) and is operated by the Jet Propulsion Laboratory under contract with NASA. Comprising a fully steerable 70-meter-diameter antenna that can transmit 500 kilowatts of waves with a length of nearly 4 centimeters, this radar has a significant capability for observing echoes from NEOs. It can see approximately 80 percent of the total sky over the course of a day (i.e., every part north of −35° latitude).The Goldstone antenna’s primary mission is spacecraft communications, and it is available for astronomy observations only a few percent



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