Polarization switching lidar device and method

• US 8,054,464 B2
• Filed: 01/25/2010
• Issued: 11/08/2011
• Est. Priority Date: 01/25/2010
• Status: Active Grant

• Current Assignee: Droplet Measurement Technologies LLC
• Original Assignee: Sigma Space Corp. (Hexagon AB)
• Inventors: Zheng, Yunhui, Leventhal, Edward Lee, Mathur, Savyasachee Liptarag
• Primary Examiner(s): Ton; Tri T
• Application Number:
  US12/693,172
• Publication Number:
  US 20110181881A1
• Time in Patent Office: 652 Days
• Field of Search: 356335-343, 250/334, 250/332, 250/330, 342/33, 342/23, 342/188, 342/5
• US Class Current: 356/342
• CPC Class Codes: G01N 15/0205 by optical means
• CPC Class Codes: G01N 2015/0092 Monitoring flocculation or agglomeration
• CPC Class Codes: G01N 2021/1795 Atmospheric mapping of gases
• CPC Class Codes: G01N 2021/216 using circular polarised light
• CPC Class Codes: G01N 2021/217 Measuring depolarisation or comparing polarised and depolarised parts of light
• CPC Class Codes: G01N 2021/4709 Backscatter
• CPC Class Codes: G01N 2021/4792 Polarisation of scatter light
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/499 using polarisation effects
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A polarization switching lidar device is arranged for remote detection and characterization of airborne aggregations of particulates. It includes a pulsed laser, a mirror, a polarizing beam splitter, an actively controlled retarder arranged to be controllably alternated between a zero retardation state and a quarter-wave retardation state such that the transmitted portion of the exiting laser light beam is linearly polarized in a predetermined direction when the actively controlled retarder is in the zero retardation state, while being circularly polarized in a predetermined rotational sense when the actively controlled retarder is in the quarter-wave retardation state. A directable telescoping assembly is arranged to collect photons backscattered by the airborne aggregations of particulates and to redirect the collected portion of depolarized backscattered photons onto the polarizing beam splitter. A photodetector is arranged to generate at least one electronic signal proportional to the collected portion of depolarized backscattered photons.

Claims

1. A polarization switching lidar device for remote detection and characterization of at least one airborne aggregation of particulates comprising:

a source of a polarized pulsed laser light beam;

a direction controlling mirror arranged to reflect the polarized pulsed laser light beam and redirect the reflected polarized pulsed laser light beam;

a polarizing beam splitter arranged to intersect the reflected polarized pulsed laser light beam and to redirect a portion of the reflected polarized pulsed laser light beam;

an actively controlled retarder arranged to intersect the redirected portion of the reflected polarized pulsed laser light beam, and to be controllably alternated between a zero retardation state and a quarter-wave retardation state such that the transmitted portion of the polarized pulsed laser light beam exiting the actively controlled retarder is linearly polarized in a predetermined direction when the actively controlled retarder is in the zero retardation state, while the transmitted portion of the polarized pulsed laser light beam exiting the actively controlled retarder is circularly polarized in a predetermined rotational sense when the actively controlled retarder is in the quarter-wave retardation state;

a directable telescoping assembly arranged to intersect the transmitted portion of the polarized pulsed laser light beam exiting the actively controlled retarder and to controllably redirect the intersected polarized pulsed laser light beam into a predetermined space angle while collecting at least a portion of depolarized backscattered photons from the scanned polarized pulse laser light beam backscattered by the at least one airborne aggregations of particulates, and to redirect the collected portion of depolarized backscattered photons onto the polarizing beam splitter;

an optical matcher arranged to collect a fraction of backscattered photons exiting the polarizing beam splitter and focus the collected fraction of depolarized backscattered photons onto a photodetector arranged to generate at least one electronic signal proportional to the collected portion of depolarized backscattered photons.

2. The polarization switching lidar device of claim 1, wherein the source of the polarized pulsed laser light beam includes a laser head and a half-wave plate.

3. The polarization switching lidar device of claim 2, wherein the laser head incorporates a laser chosen from a set of lasers consisting of laser diodes, fiber lasers, diode-pumped solid-state lasers, and lamp-pumped solid-state lasers.

4. The polarization switching lidar device of claim 2, wherein the half-wave plate is arranged to adjust a linear polarization of the polarized pulsed laser light beam emitted by the laser head.

5. The polarization switching lidar device of claim 1, wherein the polarizing beam splitter is rotationally oriented to optimally redirect the portion of the reflected polarized pulsed laser light beam.

6. The polarization switching lidar device of claim 5, wherein the polarizing beam splitter is chosen from the set of polarizing beam splitters consisting of thin film plate polarizing beam splitter, holographic polarizing beam splitter, polarizing beam splitter cube, Nicol prism, Wollaston prism, Glan-Thomson prism, Glan-Taylor prism, Glan-Foucault prism, Sé

narmont prism, and Rochon prism.

7. The polarization switching lidar device of claim 1, wherein the actively controlled retarder is a voltage-controlled retarder chosen from a set consisting of liquid crystal retarders, voltage-controlled wave plates, and Pockels cells.

8. The polarization switching lidar device of claim 1, wherein the actively controlled retarder exhibits a transition time between the zero retardation state and the quarter-wave retardation state between 5 μ

s and 100 μ

s.

9. The polarization switching lidar device of claim 1, wherein the actively controlled retarder exhibits a transition time between the zero retardation state and the quarter-wave retardation state does not exceed 50 ns.

10. The polarization switching lidar device of claim 1, wherein the directable telescoping assembly incorporates an internal scanning device arranged between principal optical elements of a scanning telescope.

11. The polarization switching lidar device of claim 1, wherein the directable telescoping assembly incorporates an external scanning device arranged outside of an optical path between principal optical elements of a scanning telescope.

12. The polarization switching lidar device of claim 1, wherein the sirectable telescoping assembly incorporates a telescope arranged in a telescope configuration chosen from a group of telescope configurations consisting of Galilean, Keplerian, Newtonian, Cassegrain, Maksutov-Cassegrain, Argunov-Cassegrain, Ritchey-Chratien, Dall-Kirkham, Gregorian, Hershelian, Schiefspiegler, Yolo, and any combination of the listed telescope configurations.

13. The polarization switching lidar device of claim 1, wherein the optical matcher includes a narrow band pass filter and at least one lens.

14. The polarization switching lidar device of claim 1, wherein the photodetector is arranged to generate at least one time-dependent analog electronic signal proportional to the collected fraction of depolarized backscattered photons and to digitize the least one time-dependent analog electronic signal into at least one time-dependent digital signal stored in a memory unit.

15. The polarization switching lidar device of claim 14, including a control unit arranged to control timing of alternations of the actively controlled retarder between the zero retardation state and the quarter-wave retardation state and to synchronize the memory unit arranged sequentially store at least two separate sequences of the at least one time-dependent digital signal so that wherein one of the at least two separate sequences detected during the zero retardation state is stored in at least one segment of the memory unit, while another of the at least two sequences of the at least one time-dependent digital signal detected during the quarter-wave retardation state is stored in at least another segment of the memory unit.

16. The polarization switching lidar device for remote detection and characterization of an airborne aggregations of particulates of claim 1, wherein the polarization switching lidar device is arranged in at least semi-stationary position on an observation surface having an average observation surface altitude and arranged to detect and characterize the airborne aggregations of particulates having an average altitude greater than the average observation surface altitude.

17. The polarization switching lidar device for remote detection and characterization of an airborne aggregations of particulates device of claim 1, wherein the polarization switching lidar device is arranged in at least semi-stationary position on an observation surface having an average observation surface altitude and arranged to detect and characterize the airborne aggregations of particulates having an average altitude smaller than or equal to the average observation surface altitude.

18. The polarization switching lidar device of claim 16, wherein the airborne aggregations of particulates include particulates in at least one cloud at an altitude greater than the average altitude of the observation surface.

19. The polarization switching lidar device of claim 18, wherein the particulates in the at least one cloud include particulates from the set of particulates consisting of water droplets, ice crystals, droplets of acidic solutions, solid particulates incorporating carbon, solid particulates incorporating soil dust, and mixtures and combinations of listed particulates.

20. The polarization switching lidar device for remote detection and characterization of an airborne aggregations of particulates device of claim 1, wherein the polarization switching lidar device is arranged on a flying vehicle, flying at an predetermined altitude, and the polarization switching lidar device is directed substantially downward so as to detect and characterize the airborne aggregations of particulates in the atmosphere at variable altitudes lower than the predetermined altitude of the flying vehicle.

21. The polarization switching lidar device of claim 16, wherein the characterization of at least one airborne aggregation of particulates includes at least a position determination of a source of the at least one airborne aggregation of particulates based on changes in the at least one electronic signal proportional to the collected fraction of depolarized backscattered photons.

22. The polarization switching lidar device of claim 18, wherein the characterization of at least one airborne aggregation of particulates includes determination of at least a position and a probable habitude of a source of the at least one airborne aggregation of particulates based on changes in the at least one electronic signal proportional to the collected fraction of depolarized backscattered photons.

23. A method for remote detection and characterization of at least one airborne aggregation of particulates utilizing a polarization switching lidar device, the method comprising:

generating a linearly polarized pulsed laser light beam having a predetermined direction of linear polarization;

using at least one the actively controlled retarder, sequentially controllably switching a polarization state of the polarized pulsed laser light beam between a circularly polarized state polarized into a predetermined rotational sense, when the at least one actively controlled retarder is controllably switched into a quarter-wave retardation state, and into a linearly polarized state linearly polarized in a direction substantially equivalent to the predefined direction of linear polarization when the at least one actively controlled retarder is controllably switched into a zero retardation state such that a transmitted portion of polarized pulsed laser light beam exiting the at least one actively controlled retarder is linearly polarized in the predetermined polarization direction when the at least one actively controlled retarder is in the zero retardation state while the transmitted portion of polarized pulsed laser light beam exiting the at least one actively controlled retarder is circularly polarized having the predetermined rotational sense when the at least one actively controlled retarder is in the quarter-wave retardation state;

scanning the transmitted portion of polarized pulsed laser light beam exiting the actively controlled retarder by at least one telescoping assembly arranged to intersect the transmitted portion of polarized pulsed laser light beam exiting the actively controlled retarder and controllably redirect the intersected polarized pulsed laser light beam into a predetermined space angle toward at least one airborne aggregation of particulates;

backscattering the scanned transmitted portion of the polarized pulsed laser light beam sequentially polarized into the circularly polarized state having the predetermined rotational sense and into the linearly polarized state having the predetermined polarization direction so that a fraction of photons scatters back from at least one airborne aggregation of particulates such that the photons in circularly polarized state having the predetermined rotational sense acquire an opposite rotational sense of circular polarization, while at least a fraction of photons polarized in the predetermined linearly polarized state, when scattered back, acquires a linear polarization state polarized in an orthogonal direction relative to the predetermined direction of linear polarization;

collecting photons from the predetermined space angle and redirecting the collected photons onto the actively controlled retarder by the at least one telescoping assembly;

sequentially converting by the actively controlled retarder in the quarter-wave retardation state the collected backscattered photons having the circularly polarized state polarized in the opposite rotational sense relative to the rotational sense of the predetermined sense of circular polarization into the linearly polarized state having the polarization state polarized in an orthogonal direction relative to the predetermined direction of linear polarization, while transmitting the scattered back photons polarized in the linear polarization state having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization when the actively controlled retarder in the zero retardation state, and redirecting the converted photons onto the polarizing beam splitter;

selectively separating the converted photons collected sequentially onto the polarizing beam splitter by transmitting only the linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization;

optically matching the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization using an optical matcher arranged to collect at least a fraction of the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization and focus the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization onto a photodetector arranged to generate at least two electronic signals proportional to the transmitted linearly polarized photons having orthogonal direction of linear polarization relative to the predetermined direction of linear polarization;

separating at least one electrical signal of the at least two electrical signals, the separated at least one electrical signal being generated during the quarter-wave retardation state, from the at least another electrical signal, the at least another electrical signal being generated during the zero retardation state of the actively controlled retarder, and storing the separated signals into at least two dedicated memory sections.

24. The method for remote detection and characterization of at least one airborne aggregation of particulates of claim 23, including a step of redirecting a transmitted portion of the linearly polarized pulsed laser light beam by a polarizing beam splitter arranged to intersect the linearly polarized pulsed laser light beam.

25. The method for remote detection and characterization of at least one airborne aggregation of particulates of claim 23, wherein the polarization switching lidar device is arranged in at least semi-stationary position on an observation surface having an average altitude and directed substantially upward so as to detect and characterize the airborne aggregations of particulates.

26. The method for remote detection and characterization of at least one airborne aggregation of particulates of claim 23, wherein the airborne aggregations of particulates include particulates in at least one cloud at an altitude greater than the average altitude of the observation surface.

27. The method for remote detection and characterization of at least one airborne aggregation of particulates of claim 25, wherein the particulates in the at least one cloud include particulates from the set of particulates consisting of water droplets, ice crystals, droplets of acidic solutions, solid particulates incorporating carbon, solid particulates incorporating soil dust, and mixtures and combinations of listed particulates.

28. The method for remote detection and characterization of at least one airborne aggregation of particulates of claim 23, wherein the polarization switching lidar device is arranged on a flying vehicle, flying at a predetermined altitude, and the polarization switching lidar device is directed substantially downward so as to detect and characterize the airborne aggregations of particulates in the atmosphere at variable altitudes lower than the predetermined altitude of the flying vehicle.

29. The method for remote detection and characterization of at least one airborne aggregation of particulates of claim 23, wherein the characterization of at least one airborne aggregation of particulates includes at least a position determination of a source of the at least one airborne aggregation of particulates based on changes in the at least one electronic signal proportional to the collected fraction of depolarized backscattered photons.

30. The method for remote detection and characterization of at least one airborne aggregation of particulates of claim 23, wherein the characterization of at least one airborne aggregation of particulates includes determination of at least a position and a probable habitude of a source of at least one airborne aggregation of particulates based on changes in the at least one electronic signal proportional to the collected fraction of depolarized backscattered photons.