US radar paparazzi snap 'Halloween Asteroid'

I am not a Radio Astronomer, but

It's not a picture, it's a delay-Doppler image -- which is a graph.

A radar pulse doesn't come back as a 2D spacial signal. It's come back as a "point" spread out in time and smeared across frequencies. That's plotted as:

x= frequency

y = time

pixel[ x, y ] = intensity

Image a plotter with multiple heads drawing wiggly lines on a roll of paper -- like a cinema polygraph. Each column of pixels is the output of one plotter head, plotting the signal received at a particular frequency. The brighter the pixel, the bigger the spike the plotter-head produced.

So the (y-axis) is just the distance from the receiver (the path-length). I'm using Radio Astronomy 101 here, but I presume the top pixels are the ones received first so produce the strongest signal.

The x-axis comes about because the asteroid is rotating and so the frequency of the pulse is Doppler shifted.

It can be the shadow from the radar signal itself. It doesn't have to be a bistatic radar to indicate shadow.

The worst kind of space potato

Re: And when, eventually, one stikes earth . . . .

My guess is the biggest danger globally of an impact event is whether it causes a flood basalt near the antipodes to its impact (600m wouldn't I believe). The link between massive volcanism and extinction events is stronger than impact events. Especially since volcanism has also been found near the same geological time of most of the big impact events as well.

Re: "transmited high-power microwaves toward the asteroid"

No, but any birds in the way would be well done.