Remote measurement of shallow depths in semi-transparent media

Patent metadata

Field	Value
Publication number	US-11231502-B2
Application number	US-201815949921-A
Country	US
Kind code	B2
Filing date	Apr 10, 2018
Priority date	Jun 30, 2011
Publication date	Jan 25, 2022
Grant date	Jan 25, 2022

Abstract

Through discrimination of the scattered signal polarization state, a lidar system measures a distance through semi-transparent media by the reception of single or multiple scattered signals from a scattering medium. Combined and overlapped single or multiple scattered light signals from the medium can be separated by exploiting varying 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 two surface timing measurements and achieving sub-pulse width resolution.

First claim

What is claimed:

1. A method of mapping a surface topography, comprising:
generating a pulse of polarized light;
scattering at least some portion of the pulse of polarized light onto two or more surfaces comprising a first surface and a second surface;
receiving the scattered light from the first surface and the second surface as a first received pulse and a second received pulse, wherein the first received pulse and the second received pulse have a one or more portions that overlap in an ambiguous intrapulse overlap portion;
separating the first received pulse and the second received pulse into a first component and a second component, the first component and the second component having a relative difference in polarization between each other, wherein the separation removes the ambiguous intrapulse overlap portion;
determining an amount of time elapsed between the first component and the second component; and
calculating a relative distance between the first surface and the second surface based on the amount of time elapsed, thereby achieving a sub-pulse width resolution.

2. The method of claim 1 , wherein one of the two or more surfaces comprises a relatively polarization preserving surface.

3. The method of claim 1 , wherein the generating a pulse of polarized light step comprises the steps of generating a light pulse with a laser; and passing the light pulse through a polarizer.

4. The method of claim 1 , wherein the first component is a co-planar polarization component of the scattered light and the second component is a cross-planar component of the scattered light.

5. The method of claim 1 , wherein the receiving the scattered light step comprises the step of collecting the scattered light through a telescope.

6. The method of claim 1 , further comprising dynamically adjusting scanner parameters to keep a spot density relatively constant as at least one of an aircraft flying height and ground terrain elevation changes during a survey mission.

7. The method of claim 6 , wherein the dynamically adjusting scanner parameters comprises a galvanometer-based scanner configured to execute a swath-tracking algorithm for maintaining a predetermined laser spot density on the one or more surfaces.

8. The method of claim 7 , wherein laser spot density is constant as an elevation changes between one or more surfaces.

Assignees

• Univ Colorado Regents
• Astra Lite Inc

Inventors

• Thayer Jeffrey P
• Crowley Geoffrey
• Gisler Andrew W
• Mitchell Steven
• Hayman Matthew

Classifications

• G01S17/89 Primary

  for mapping or imaging · CPC title

• G01S17/42

  Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46) · CPC title

• G01S7/4817

  relating to scanning · CPC title

• G01S7/4865

  Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak (peak detection in noise, signal conditioning G01S7/487) · CPC title

• G01C7/02

  of land surfaces · CPC title