We do that now with spread-spectrum and chirps - you correlate the signal sent with the return signal and you can pick out reflections below the noise threshold

We do that now with spread-spectrum and chirps - you correlate the signal sent with the return signal and you can pick out reflections below the noise threshold. https://en.wikipedia.org/wiki/Pulse_compression https://en.wikipedia.org/wiki/Pulse_compression I'm guessing that this might be more effective at very small returns, where the reflection is so small that it suffers from shot noise - the fact that the energy comes in discrete packets makes it hard to correlate. This is another way to verify that the photons received are the same ones sent out (and not background noise)