There's a very nice
press release from the NRAO describing the process of obtaining radar images of asteroids and, in particular, NEO.
A team of astronomers using the National Science Foundation's Green Bank Telescope (GBT) in West Virginia and NASA's Deep Space Network radar transmitter at Goldstone, California, has made the most detailed radar images yet of asteroid 2004 BL86.
The images, which were taken early in the morning on Jan. 27, 2015, reveal the asteroid's surface features in unprecedented clarity. At the time of the observations, the asteroid was traveling away from the Earth, so its distance varied from 1.3 million to 1.6 million kilometers, or about three-and-a-half to four times the distance from the Earth to the Moon.