How does PLANETARY RADAR actually work?

Arecibo was condemned a couple weeks ago, and collapsed a couple days ago as a result of a minor earthquake and well-overdue maintenance. Unfortunately, this deprives the world of its largest Radar Telescope, and radar telescopes are awesome! I've had a really hard time in the past finding good descriptions of how radar astronomy actually works - how do you take a picture of something so far away that the beam diverges by the time it gets there, and diverges even more by the time it gets back!? The answer is math and approximation. Asteroid "images" are actually not any sort of photograph, but reconstructions based on timing and spectroscopy of radar signals. I'm really happy with how all the animations and whatnot came out, and I hope you like my explanation of delay-doppler imaging! I think it's an absolutely fascinating technique that's seen as just too counterintuitive to get a lot of recognition. Delay-Doppler images aren't really "pictures", but they are sure valuable to researchers (and every human living on Earth under threat of asteroid impact!) Share this video with anybody who wants to appreciate how important Arecibo was, and what such an awesome unique instrument was capable of. #Arecibo #RebuildTheAreciboObservatory #Asteroids Music in this video: I Dunno by grapes is licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/...) http://ccmixter.org/files/grapes/16626 Other media in this video: Lots of public-domain NASA images, and: https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://en.wikipedia.org/wiki/Microwa... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://en.wikipedia.org/wiki/Moon#/m... https://en.wikipedia.org/wiki/Klystro... https://en.wikipedia.org/wiki/Azimuth... https://en.wikipedia.org/wiki/Azimuth... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi...