Spectrally dispersive imaging lidar system

• US 5,257,085 A
• Filed: 04/24/1991
• Issued: 10/26/1993
• Est. Priority Date: 04/24/1991
• Status: Expired due to Fees

• Current Assignee: Kaman Aerospace Corporation Corporation of Delaware
• Original Assignee: Kaman Aerospace Corporation (Kaman Corporation)
• Inventors: Smith, Duane, Keeler, R. Norris, Ulich, Bobby L.
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US07/690,767
• Time in Patent Office: 916 Days
• Field of Search: 356/301, 356/317, 356/318, 356/326, 356/328, 356/73, 358/95
• US Class Current: 356/73
• CPC Class Codes: G01J 3/2823 Imaging spectrometer
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
• CPC Class Codes: G01N 2021/655 Stimulated Raman
• CPC Class Codes: G01N 21/64 Fluorescence; Phosphorescence
• CPC Class Codes: G01N 21/6456 Spatial resolved fluorescence measurements; Imaging
• CPC Class Codes: G01N 21/65 Raman scattering
• CPC Class Codes: G01S 17/02 Systems using the reflection of electromagnetic waves other than radio waves G01S17/66 takes precedence
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/484 Transmitters

Abstract

An imaging UV/visible fluorosensing and Raman lidar system comprises an optical sensor for simultaneously measuring temporally, spatially and spectrally resolved laser backscatter from on the land, on or beneath the surface of bodies of water and in the atmosphere. The present invention utilizes "active" interrogation or "passive" interrogation for remotely and non destructively probing the spectrally-dependent optical properties of a scene. In the "active" mode, the optical sensor of this invention comprises a transmitter (preferably a tunable solid state laser) which emits pulses of coherent light through a variable or adjustable field-of-view telescope whereupon the light pulses are then propagated towards a scene (e.g., land, sea or atmosphere). Thereafter, laser backscatter is collected by a second variable field-of-view telescope and directed to an imaging system and spectrally dispersive optical subsystem.

Claims

1. A method for remotely and non-destructively probing the spectrally, temporally and distance-dependent optical properties of a target volume using a single integrated optical sensor having multiple modes of operation including an imaging mode and a spectral analysis mode, including the steps of:

selecting a mode of operation for the optical sensor to operate in an imaging mode or a spectral analysis mode with said imaging mode including steps (a)-(e) and said spectral analysis mode including steps (f)-(i);

(a) selectively generating short pulses of light using laser transmitter means;

(b) projecting said short pulses of light toward the backscattering medium and at a target volume enveloped by the medium;

(c) receiving said pulses of light backscattered from said target volume after a time delay corresponding to the round-trip propagation time of said light pulses to and from said target volume using receiver means;

(d) converting said received pulses of light to a video image of said target defining a target volume image, said target volume image having an image intensity pattern associated therewith; and

(e) scanning the wavelength of the laser transmitter means to identify the wavelength-dependent differences in said image intensity pattern to thereby improve said video image of said target volume image;

(f) generating short pulses of light from laser transmitter means;

(g) projecting said generated short pulses of light toward a target volume;

(h) detecting said pulses of light backscattered from said target volume after a selected time delay using gated detector means; and

(i) spectrally analyzing said detected pulses of light in spectrometer means to create a selected spectra of said target volume.

2. The method of claim 1 wherein in said imaging mode:

said laser transmitter means has an operating wavelength and includes means for tuning said operating wavelength.

3. The method of claim 1 wherein in said imaging mode said projecting step includes the step of projecting said pulses of light through a first variable field-of-view telescope and wherein said receiving step includes the step of:

receiving said reflected pulses of light in a second variable field-of-view telescope.

4. The method of claim 3 including the step of

maintaining the field-of-view in each of said first and second telescopes as equal.

5. The method of claim 1 wherein in said imaging mode said projecting step includes the step of projecting said pulses of light through variable field-of-view telescope means and wherein said receiving step includes the step of receiving said reflected pulses of light from said variable field-of-view telescope means.

6. The method of claim 1 wherein in said imaging mode said scanning step is controlled by at least one of the wavelength controlling means selected from the group consisting of harmonic generator means, Raman shifter means and optical parameter oscillator means.

7. The method of claim 1 wherein:

said selected spectra comprises emission spectra.

8. The method of claim 7 including the steps of:

selecting the operating wavelength of said laser transmitter means for excitation of fluorescence in said target volume; and

measuring the emission spectra to analyze said target volume.

9. The method of claim 8 wherein:

said emission spectra is analyzed for detection of chemical species in said target volume.

10. The method of claim 1 wherein:

said selected spectra comprises excitation spectra.

11. The method of claim 1 including the steps of:

selecting a first operating wavelength of said laser transmitter for excitation of fluorescence in said target volume;

measuring a first emission spectra of the excited target volume derived from said first operating wavelength;

selecting a second operating wavelength of said laser transmitter for excitation of fluorescence in said target volume;

measuring a second emission spectra of the excited target volume derived from said second operating wavelength;

comparing said first and second emission spectra to analyze said target volume.

12. The method of claim 11 wherein said target volume comprises an oil slick wherein:

said comparing step identifies at least one parameter of the oil in said oil slick.

13. The method of claim 1 including the step of:

calibrating the operating wavelength of said laser transmitter means using laser wavemeter means and comparing an output from said laser wavemeter means with an output from said spectrometer means.

14. The method of claim 1 wherein:

said selected spectra comprise Raman scattering spectra.

15. The method of claim 14 including the step of:

passing said detected pulses of light through laser line rejection filter means to improve said Raman scattering spectra.

16. The method of claim 15 including the step of:

positioning said laser line rejection filter either before said gated detector means or before said spectrometer means.

17. The method of claim 14 wherein said reflected pulses of light include Raman scattering spectra and spontaneous electronic emission spectra which has larger cross-sections than said Raman scattering spectra and including the step of:

rejecting said spontaneous electronic emission spectra from said Raman scattering spectra to improve said Raman scattering spectra.

18. The method of claim 17 wherein:

said rejecting step is accomplished by selected time delay of said gated detector means.

19. The method of claim 18 wherein said projecting step includes the step of projecting said pulses of light through a first variable field-of-view telescope and wherein said receiving step includes the step of:

receiving said reflected pulses of light in a second variable field-of-view telescope.

20. The method of claim 19 including:

adjusting the field-of-view in said first and second telescopes to increase laser power density of said laser transmitter means.

21. The method of claim 1 wherein said projecting step includes the step of projecting said pulses of light through variable field-of-view telescope means and wherein said receiving step includes the step of receiving said reflected pulses of light from said variable field-of-view telescope means.

22. The method of claim 14 including the step of:

non-linearly optically shifting said laser transmitter means to thereby shorten wavelengths of pulsed light generated by said laser transmitter means thereby improving said Raman scattering spectra.

23. The method of claim 19 including the step of:

narrowing the field-of-view of said second telescope to match the field-of-view of said first telescope.

24. The method of claim 1 wherein:

said spectrometer means comprises flat field monolithic spectrometer means.

25. The method of claim 1 including the steps of:

anamorphically demagnifying said reflected light pulses to slit shaped light pulses; and

delivering said slit shaped light pulses to an input slit in said spectrometer means.

26. The method of claim 1 wherein said spectrometer means comprises:

laser line rejection filter means;

diffraction grating means in optical communication with said rejection filter means; and

detector array means in optical communication with said diffraction grating means.

27. The method of claim 26 including:

at least one prism pre-disperser communication with said laser line rejection filter means.

28. The method of claim 1 wherein said spectrometer means comprises:

laser line rejection filter means;

at least one prism dispersion means in optical communication with said rejection filter means;

intensifier means in optical communication with said prism disperser means; and

detector array means in optical communication with said intensifer means.

29. A method for remotely and non-destructively probing the spectrally, temporally and distance-dependent optical properties of a target volume using a single integrated optical sensor having multiple modes of operation including an imaging mode and a spectral analysis mode, including the steps of:

selecting a mode of operation for the optical sensor to operate in an imaging mode or a temporal luminescence decay measurement mode, including the steps of;

selecting a mode of operation for the optical sensor to operate in an imaging mode or a temporal luminescence decay measurement mode with said imaging mode including steps (a)-(e) and said temporal luminescence decay measurement mode including steps (f)-(i);

(a) selectively generating short pulses of light using laser transmitter means;

(b) projecting said short pulses of light toward the backscattering medium and at a target volume enveloped by the medium;

(c) receiving said pulses of light backscattered from said target volume after a time delay corresponding to the round-trip propagation time of said light pulses to and from said target volume using receiver means;

(d) converting said received pulses of light to a video image of said target defining a target volume image, said target volume image having an image intensity pattern associated therewith; and

(e) scanning the wavelength of the laser transmitter means to identify the wavelength-dependent differences in said image intensity pattern to thereby improve said video image of said target volume image;

(f) generating short pulses of light from laser transmitter means;

(g) projecting said generated short pulses of light toward a target volume;

(h) detecting said pulses of light backscattered from said target volume after a selected time delay using gated detector means; and

(i) sweeping the selected time delay of said gated detector means for measuring the temporal luminescence decay of said target volume.

30. The method of claim 29 including the step of:

spatially resolving said temporal decay.

31. The method of claim 29 including the step of:

spectrally resolving said temporal decay.

32. The method of claim 29 wherein:

said luminescence temporal decay comprises fluorescence decay.

33. The method of claim 32 including the step of:

spectrally resolving said luminescence temporal decay at at least two different excitation wavelengths.

34. The method of claim 31 wherein said step of spectrally resolving said temporal decay utilizes an optical system comprising:

laser line rejection filter means;

at least one dispersive prism means in optical communication with said filter means;

streak camera tube means in optical communication with said dispersive prism means; and

detector array means in optical communication with said streak camera tube means.

35. The method of claim 34 including:

a plurality of dispersive prism means.

36. An apparatus for remotely and non-destructively probing the spectrally, temporally and distance-dependent optical properties of a target volume including:

a single, integrated optical sensor having multiple modes of operation including an imaging mode and a spectral analysis mode;

mode selection means for selecting a mode of operation for the optical sensor to operate in an imaging mode or a spectral analysis mode;

said imaging mode including;

(a) laser transmitting means for selectively generating short pulses of light;

(b) means for projecting said short pulses of light toward the backscattering medium and at a target volume enveloped by the medium;

(c) means for receiving said pulses of light backscattered from said target volume after a a time delay corresponding to the round-trip propagation time of said light pulses to and from said target volume using receiver means;

(d) means for converting said received pulses of light to a video image of said target defining a target volume image, said target volume image having an image intensity pattern associated therewith; and

(e) means for scanning the wavelength of the laser transmitter means to identify the wavelength-dependent differences in said image intensity pattern to thereby improve said video image of said target volume image;

said spectral analysis mode including;

(f) laser transmitting means for generating short pulses of light;

(g) means for projecting said generated short pulses of light toward a target volume;

(h) means for detecting said pulses of light backscattered from said target volume after a selected time delay using gated detector means; and

(i) spectrometer means for spectrally analyzing said detected pulses of light to create a selected spectra of said target volume.

37. The apparatus of claim 36 wherein in said imaging mode:

said laser transmitter means has an operating wavelength and includes means for tuning said operating wavelength.

38. The apparatus of claim 36 wherein in said imaging mode said means for projecting includes a first variable field-of-view telescope and wherein said means for receiving includes a second variable field-of-view telescope.

39. The apparatus of claim 36 wherein in said imaging mode said means for projecting includes variable field-of-view telescope means and wherein said means for receiving includes said variable field-of-view telescope means.

40. The apparatus of claim 36 wherein in said imaging mode said means for scanning is controlled by at least one of the wavelength controlling means selected from the group consisting of harmonic generator means, Raman shifter means and optical parameter oscillator means.

41. The apparatus of claim 36 wherein said selected spectra comprises emission spectra and including:

means for selecting the operating wavelength of said laser transmitter means for excitation of fluorescence in said target volume and;

means for measuring the emission spectra to analyze said target volume.

42. The apparatus of claim 41 wherein:

means for analyzing said emission spectra for detection of chemical species in said target volume.

43. The apparatus of claim 36 wherein said selected spectra comprises excitation spectra and including:

means for selecting a first operating wavelength of said laser transmitter for excitation of fluorescence in said target volume;

means for measuring a first emission spectra of the excited target volume derived from said first operating wavelength;

means for selecting a second operating wavelength of said laser transmitter for excitation of fluorescence in said target volume;

means for measuring a second emission spectra of the excited target volume derived from said second operating wavelength;

means for comparing said first and second emission spectra to analyze said target volume.

44. The apparatus of claim 36 including:

means for calibrating the operating wavelength of said laser transmitter means using laser wavemeter means and comparing an output from said laser wavemeter means with an output from said spectrometer means.

45. The apparatus of claim 36 wherein said selected spectra comprise Raman scattering spectra and including:

laser line rejection filter means for receiving said detected pulses of light and thereby improving said Raman scattering spectra.

46. The apparatus of claim 45 wherein:

said laser line rejection filter is positioned either before said gated detector means or before said spectrometer means.

47. The apparatus of claim 36 wherein said means for projecting includes a first variable field-of-view telescope and wherein said means for receiving includes a second variable field-of-view telescope.

48. The apparatus of claim 36 wherein said means for projecting includes variable field-of-view telescope means and wherein said means for receiving includes said variable field-of-view telescope means.

49. The apparatus of claim 36 wherein:

said spectrometer means comprises flat field monolithic spectrometer means.

50. The apparatus of claim 36 including:

means for anamorphically demagnifying said reflected light pulses to slit shaped light pulses; and

means for delivering said slit shaped light pulses to an input slit in said spectrometer means.

51. The apparatus of claim 36 wherein said spectrometer means comprises:

laser line rejection filter means;

diffraction grating means in optical communication with said rejection filter means; and

detector array means in optical communication with said diffraction grating means.

52. The apparatus of claim 51 including:

at least one prism pre-disperser means in input optical communication with said laser line rejection filter means.

53. The apparatus of claim 36 wherein said spectrometer means comprises:

laser line rejection filter means;

at least one prism dispersion means in optical communication with said rejection filter means;

intensifier means in optical communication with said prism disperser means; and

detector array means in optical communication with said intensifer means.

54. An apparatus for remotely and non-destructively probing the spectrally, temporally and distance-dependent optical properties of a target volume including:

a single, integrated optical sensor having multiple modes of operation including an imaging mode and a temporal luminescence decay measurement mode;

mode selection means for selecting a mode of operation for the optical sensor to operate in an imaging mode or a temporal luminescence decay measurement mode;

said imaging mode including;

(a) laser transmitting means for selectively generating short pulses of light;

(b) means for projecting said short pulses of light toward the backscattering medium and at a target volume enveloped by the medium;

(c) means for receiving said pulses of light backscattered from said target volume after a a time delay corresponding to the round-trip propagation time of said light pulses to and from said target volume using receiver means;

(d) means for converting said received pulses of light to a video image of said target defining a target volume image, said target volume image having an image intensity pattern associated therewith; and

(e) means for scanning the wavelength of the laser transmitter means to identify the wavelength-dependent differences in said image intensity pattern to thereby improve said video image of said target volume image;

said temporal luminescence decay measurement mode including;

(f) laser transmitter means for generating short pulses of light;

(g) means for projecting said generated short pulses of light toward the said target volume;

(h) means for detecting said pulses of light backscattered from said target volume after using a selected time delay using gated detector means; and

(i) means for sweeping the selected time delay of said gated detector means for measuring the temporal luminescence decay of said target volume.

55. The apparatus of claim 54 including:

means for spatially resolving said temporal decay.

56. The apparatus of claim 54 including:

means for spectrally resolving said temporal decay.

57. The apparatus of claim 56 wherein said luminescence temporal decay comprises fluorescence decay and including:

means for spectrally resolving said luminescence temporal decay at at least two different excitation wavelengths.

58. The apparatus of claim 56 wherein said means for spectrally resolving said temporal decay utilizes an optical system comprising:

laser line rejection filter means;

at least one dispersive prism means in optical communication with said filter means;

streak camera tube means in optical communication with said dispersive prism means; and

detector array means in optical communication with said streak camera tube means.

59. The apparatus of claim 58 including:

a plurality of dispersive prism means.