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 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.
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 a first surface and a second surface;
receiving the scattered light from the first surface and the second surface as a received pulse, wherein the received pulse has one or more portions that overlap in an ambiguous intrapulse overlap portion;
separating the ambiguous intrapulse overlap portion into a first component associated with the first surface and a second component associated with the second surface, 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 the first surface 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 the step of 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 adjusted scanner parameters comprises a galvanometer-based scanner configured to execute a swath-tracking algorithm to maintain 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.
9. 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 a water surface and a bottom surface;
receiving the scattered light from the water surface and the bottom surface as a received pulse, wherein the received pulse has an ambiguous intrapulse overlap portion;
separating the ambiguous intrapulse overlap portion into a first component associated with the water surface and a second component associated with the bottom surface based on a polarization difference between the first component and the second component;
determining an amount of time elapsed between the first component and the second component; and
calculating a relative distance between the water surface and the bottom surface based on the amount of time elapsed, thereby achieving a sub-pulse width resolution.
10. The method of claim 9 , wherein the water surface comprises a relatively polarization preserving surface.
11. The method of claim 9 , wherein the generating a pulse of polarized light step comprises:
generating a light pulse with a laser; and
passing the light pulse through a polarizer.
12. The method of claim 9 , 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.
13. The method of claim 9 , 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.
14. The method of claim 13 , wherein the dynamically adjusted scanner parameters comprises a galvanometer-based scanner configured to execute a swath-tracking algorithm to maintain a predetermined laser spot density on the one or more surfaces.
15. The method of claim 14 , wherein laser spot density is constant as an elevation changes between one or more surfaces.
16. 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 a water surface and a bottom surface;
receiving the scattered light from the water surface and the bottom surface as a received pulse, wherein the received pulse has an ambiguous intrapulse overlap portion;
isolating a water surface return and isolating a bottom surface return from the received pulse based on polarization scattering properties of the water surface and polarization scattering properties of the bottom surface;
analyzing the water surface return in a first detector to determine a first component;
analyzing the bottom surface return in a second detector that is different from the first detector to determine a second component;
determining an amount of time elapsed between the first component and the second component; and
calculating a relative distance between the water surface and the bottom surface based on the amount of time elapsed, thereby achieving a sub-pulse width resolution.
17. The method of claim 16 , wherein the water surface comprises a relatively polarization preserving surface.
18. The method of claim 16 , wherein the generating a pulse of polarized light step comprises:
generating a light pulse with a laser; and
passing the light pulse through a polarizer.
19. The method of claim 16 , 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.
20. The method of claim 16 , further comprising the step of 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.