[mikeiz404]

My guess is they are steering the radar beam from something hovering overhead.

The video links to a paper [1] titled "Airborne Circular W-Band SAR for Multiple Aspect Urban Site Monitoring" which mentions beam steering in the abstract.

1: https://ieeexplore.ieee.org/document/8701523/

[seoulmetro]

That's what I thought too, but how can there be such significant shadows? Wouldn't the shadows of any wavelength they are sending be near nothing?