Exactly this, and also that fairly respectable youtubers use those images as thumbnails further legitimising what might be wild speculation.
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Geek-out warning! You probably wonāt see any source data. Hereās what I think it would be: the wavelength of the highest frequency in X band is about 2.5 cm (25mm) for one complete waveform. Perhaps they can extract the data for pyramid-only pixels in the (10km sq) satellite image (1m sq pixels best that radar can do), then deconstruct to each individual chirpās phase/time data (waveform goes through angular changes called phase as it completes the oscillation of the waveform). A 1mm move in the surface would therefore be 1/25th of 360 degrees of the waveform. Not sure, but this would seem to require the ability to reliably extract 15 degrees of phase change for a full 1mm movement. Less than that for sub-mm movements. In theory, if the radar were perfectly perpendicular to the face of the pyramid and the face of the pyramid were perfectly flat, all chirp phase/time data would exhibit the same phase angle. Deviations from the phase angle would indicate a different distance (theyāre saying they can measure sub-mm pyramid surface movements using some undisclosed technique).
Since the radar is unlikely to be perfectly perpendicular to the face of the pyramid and the surface is rough-as-a-cob, and the pixels are 1m sq, it would take a lot of āprocessingā (smoothing of the data) to get any result. Of course errors get introduced and data gets lost during any such processing.
So, using the theoretical process above you could perhaps re-create a map of blobs of different distance (sub-mm data would be an even smaller angular change in the data) and overlay that onto an image of the pyramid from theoretically the same angle as the radar image.
Going from blobs of data to line drawings is very sketchy.
Applying the above to a solid rock foundation structure seems even more iffy than the āidealā process described above.
The above is just conjecture from a semi-informed non-professionalā¦no idea if it would work, or if itās the technique theyāre using.
Hereās a hobbyist describing his home-made radar that discusses some of the basics of phase angle.