Now, we use optical scanning telescopes with a wide field of view, and image differencing. Optical instruments have a wide field of view and don't have the inh

Now, we use optical scanning telescopes with a wide field of view, and image differencing. Optical instruments have a wide field of view and don't have the inherent SNR problems that radar does. (I.e., using the Sun to illuminate objects is more efficient than doing it yourself.) As a side-effect, there are all kinds of other transient sources that these scanning telescopes pick up, like supernovae, relativistic jets from AGNs ("blazars"), exotic variable stars, etc. (http://crts.caltech.edu http://crts.caltech.edu) It's a zoo out there! Radar does play a role in orbit characterization, and recovery of object geometry, once the NEO gets close enough. But you can get orbits through optical techniques too. The NASA center for near-Earth objects (NEOs) is: https://cneos.jpl.nasa.gov/about/search_program.html https://cneos.jpl.nasa.gov/about/search_program.html NEO close approaches to Earth, tabulated: https://cneos.jpl.nasa.gov/ca/ https://cneos.jpl.nasa.gov/ca/. There was a really close one today, actually (a 5-meter object at 0.13 lunar distances). For more about the role of planetary radar in NEOs, search for "radar" in this FAQ: https://www.nasa.gov/planetarydefense/faq https://www.nasa.gov/planetarydefense/faq