[giantrobot]

These images are confusing. The "lit" side is where the radar beam is coming from. The perspective is looking "down" on the asteroid with "up" on the image being the direction of Earth. The radar scans a beam across the object and records the reflections. The brightness of a pixel is a function of the strength, phase, and polarity of the returned signal. The position of a pixel is a function of its distance from the receiver.

From the perspective of the radar receiver it's just receiving a series of reflections over a period of time. These are processed for the above measures and then perspective transformed to show an "overhead" image that we see here.

[mturmon]

It's not a bad heuristic that the "lit" (up) side is where the radar is coming from. That's the "delay" coordinate, so the top means small delay which means close to observer.

But the other (left/right) coordinate is doppler, which does not map 1:1 to a physical location -- doppler will depend on the rotation and geometry of the asteroid.

The radar beam is not "scanning" across the object. The asteroid is too small to focus the beam on a part of it -- the beam illuminates the whole object. We get lucky that the object is spinning, so that different surfaces on the asteroid cast energy into different doppler offsets.

Anyway, the returned signal is then binned into (delay, doppler) coordinates. This is repeated for many separate pings to beat down the receiver noise.

During the observation window (series of pings), you have to compensate for the relative motion of the earth and the centroid of the target, because the relative velocity (zero-point of the doppler coordinate) is changing the whole time.