[rich_sasha]

In principle, as the sibling comment says, you could measure just the phase difference on the receiver end. The trick is that it's much harder for light frequencies than radar. I'm non even sure we can measure the phase etc of a light beam, and if we could, the Nyquist frequency is incredibly high - 2x frequency takes us to PHz frequencies.

There might be something cute you can do with interference patterns but no idea about that. We do sort of similar things with astronomic observations.