US Patent 9476980 Remote measurement of shallow depths in semi-transparent media

Through discrimination of the scattered signal polarization state, a lidar system measures a distance through semi-transparent media by the reception of scattered signals from a first surface and scattered signals from a second surface. Combined and overlapped light signals scattered from the two surface signals can be separated by exploiting their differing polarization characteristics. This removes the traditional laser and detector pulse width limitations that determine the system's operational bandwidth, translating relative depth measurements into the conditions of single surface timing measurements and achieving sub-pulse width resolution.