Frequency modulated lasar radar - Patent Review 4830486

Claims

What is claimed is:

1. An apparatus for measuring the distance to an arbitrary target, said apparatus comprising:

radiation source means for producing a beam of coherent radiation, said radiation source means including frequency modulating means for frequency sweep modulating the frequency of said radiation;

first beam splitting means, optically coupled to said radiation source means, for dividing said beam into a ranging beam and a reference beam;

ranging interferometer means, optically coupled to said first beam splitting means, for directing a first portion of said ranging beam along a path toward said target and for producing a first wave interference pattern between a second portion of the ranging beam travelling over a first path and the first portion of the ranging beam scattered by said target, said ranging interferometer means including focusing means for focusing said ranging beam first portion onto said target;

reference interferometer means, optically coupled to said first beam splitting means, for directing a first portion of said reference beam along a reference path of fixed predetermined known length and for producing a second wave interference pattern between a second portion of said reference beam travelling over a second path and the first portion of said reference beam travelling over said reference path;

processing means, responsive to said first and second wave interference patterns, for determining the length of path between said ranging interferometer means and said target, said processing means including tracking filter means for filtering noise from said first wave interference pattern; and

surface roughness processing means, responsive to the amplitude of said first wave interference pattern produced by said ranging interferometer means, for characterizing the roughness of the scattering surface to said target.

2. An apparatus as in claim 1 wherein said surface roughness processing means includes:

means for varying the angle of incidence of said beam on said surface;

means, coupled to said ranging interferometer means, for detecting the amplitude of said first wave interference pattern, said detected amplitude proportional to the intensity of the radiation scattered by said surface; and

data processing means for processing the detected amplitude of said first wave interference pattern for a plurality of angles of incidence to produce indicia of said surface roughness.

3. An apparatus as in claim 2 wherein said angle varying means includes means for changing the position of said target.

4. An apparatus as in claim 2 wherein angle varying means includes means for changing the direction of the first portion of said ranging beam.

5. An apparatus as in claim 2 wherein:

said ranging interferometer means includes means for successively directing said first portion of said ranging beam onto a plurality of points on said surface of said target; and

said data processing means includes:

means for storing the determined length of the path from said ranging interferometer means to each of said plurality of points on said surface; and

means for estimating the angle of incidence of said first portion of said ranging beam on each of said plurality of points from said determined length of the paths to said plurality of points.

6. An apparatus as in claim 2 wherein said data processing means includes:

means for storing experimentally-obtained data comprising sets of a plurality of intensities of scattered coherent radiation as a function of angle of incidence for a plurality of different predetermined surfaces; and

means for comparing said detected intensities for a plurality of angles of incidence with said stored sets in order to approximate the roughness of said surface by the roughness of one of said predetermined surfaces.

7. An apparatus as in claim 2 wherein:

said amplitude-detecting means further includes means for characterizing modulations in the scattered radiation, said modulations produced by interference between radiation scattered by different points of said surface; and

said data processing means further includes means for deriving, from said characterization of the modulations, indicia of the roughness of said surface.

8. An apparatus as in claim 7 wherein:

said means for characterizing includes:

means for measuring the peak-to-peak amplitude of said modulations; and

means for measuring the angular displacement of said modulations; and said deriving means includes:

means for storing experimentally-obtained data comprising the peak-to-peak amplitudes and angular displacements of the modulations in coherent radiation scattered by a plurality of different predetermined surfaces, said modulations for each of said different surfaces produced by interference between radiation scattered by different points on said each surface; and

means for comparing said measured peak-to-peak amplitude and angular displacement data with said stored peak-to-peak amplitude and angular displacement data in order to approximate the roughness of said surface by the roughness of one of said predetermined surfaces.

9. An apparatus as in claim 1 wherein said surface roughness processing means includes:

detecting means, coupled to said ranging interferometer means, for detecting the amplitude of said first wave interference pattern, said detected amplitude proportional to the intensity of the radiation scattered by the surface;

characterizing means, responsive to said detected amplitudes, for characterizing modulations in the scattered radiation, said modulations produced by interference between portions of said first portion of said ranging beam scattered by different points on said surface; and

means for deriving, from said characterization of the modulations, indicia of the roughness of said surface.

10. An apparatus as in claim 9 wherein:

said means for characterizing includes:

means for measuring the peak-to-peak amplitude of said modulations; and

means for measuring the angular displacement of said modulations; and said deriving means includes:

means for storing experimentally-obtained data comprising the peak-to-peak amplitudes and angular displacements of the modulations in coherent radiation scattered by a plurality of different predetermined surfaces, said modulations for each of said different surfaces produced by interference between radiation scattered by different points on said each surface; and

means for comparing said measured peak-to-peak amplitude and angular displacement data with said stored peak-to-peak amplitude and angular displacement data in order to approximate the roughness of said surface by the roughness of one of said predetermined surfaces.

11. An apparatus as in claim 10 wherein said characterizing means includes means for scanning said first portion of said ranging beam over said surface.

12. An apparatus as in claim 10 wherein said characterizing means includes means for changing the angle of incidence of said beam on said surface.

13. An apparatus for measuring the distance to an arbitrary target, said apparatus comprising:

radiation source means for producing a beam of coherent radiation, said radiation source means including means for sweeping the frequency of said produced radiation from a first to a second frequency, said sweep defined by a continuously increasing function of time;

first star coupling means, including an input port and first and second output ports, said radiation source means coupled to said input port, said first star coupling means for splitting said beam produced by said radiation source means into a ranging beam and a reference beam, said ranging beam exiting said first star coupling means at said first output port, said reference beam exiting said first star coupling means at said second output port;

ranging beam splitting star coupling means, including an input port and first and second output ports, for splitting said ranging beam into first and second beams, said first beam produced at said first output port, said second beam produced at said second output port, said ranging beam splitting star coupling means including means for coupling said input port of said ranging beam splitting star coupling means to said first output port of said first star coupling means;

first lens means, coupled to said first output of said ranging beam splitting star coupling means, for focusing said first beam on said target;

ranging beam combining star coupling means for combining said first and second beams to produce a first wave interference pattern, said ranging beam combining star coupling means including first and second input ports and at least one output port;

first optical fiber means for coupling said second output port of said ranging beam splitting star coupling means to said second input port of said ranging beam combining star coupling means, said first optical fiber means defining a fixed path length;

second lens means positioned in proximity with said first lens means and aimed at said target, for coupling a portion of said first beam scattered by said target to said first input port of said ranging beam combining star coupling means;

ranging detector means, coupled to said output port of said ranging beam combining star coupling means, for detecting the fringes in said first wave interference pattern;

ranging counting means, responsive to said detected fringes of said ranging detector means, for counting the number of fringes N.sub.r in said first wave interference pattern produced during said sweep in frequency;

reference beam splitting star coupling means, including an input port and first and second output ports, for splitting said ranging beam into third and fourth beams, said third beam produced at first output port, said fourth beam produced at said second output port, said reference beam splitting star coupling means including means for coupling said input port of said reference beam splitting star coupling means to said second output port of said first star coupling means;

reference beam combining star coupling means for combining said third and fourth beams to produce a second wave interference pattern, said reference beam combining star coupling means including first and second input ports and at least one output port;

second optical fiber means for coupling said second output port of said reference beam splitting star coupling means to said second input port of said reference beam combining star coupling means, said second optical fiber means defining a fixed path length;

reference optical fiber means for coupling said first output port of said reference beam splitting star coupling means to said first input port of said reference beam combining star coupling means, said reference optical fiber means defining a path of predetermined known fixed length X.sub.ref, X.sub.ref being approximately equal to the distance R to be measured;

reference detector means, coupled to said output port of said reference beam combining star coupling means, for detecting the fringes in said second wave interference pattern;

reference counting means, responsive to said detected fringes of said references detector means, for counting the number of fringes N.sub.ref in said second wave interference pattern produced during said sweep in frequency;

tracking filter means, connected between said ranging detector means and said ranging counting means, for filtering noise from said first pattern detected fringes;

processing means, responsive to said counts N.sub.r and N.sub.ref, for calculating the distance R to said target, said distance R given by ##EQU52## and surface roughness processing means, responsive to the amplitude of the fringes detected by said ranging detector means, for characterizing the roughness of the scattering surface of said target scattering said first beam.

14. An apparatus as in claim 13 wherein said surface roughness processing means includes:

means for varying the angle of incidence of said first beam on said surface;

means, coupled to said ranging detector means, for measuring the amplitude of said first wave interference pattern, said measured amplitude proportional to the intensity of the portion of said first beam scattered by said surface; and

data processing means for processing said measured amplitude of said first wave interference pattern for a plurality of angles of incidence to produce indicia of said surface roughness.

15. An apparatus as in claim 14 wherein said data processing means includes:

means for storing experimentally-obtained data comprising sets of a plurality of intensities of scattered coherent radiation as a function of angle of incidence for a plurality of different predetermined surfaces; and

means for comparing said detected intensities for a plurality of angles of incidence with said stored sets in order to approximate the roughness of said surface by the roughness of one of said predetermined surfaces.

16. An apparatus as in claim 14 wherein said:

said amplitude measuring means further includes means for characterizing amplitude modulations in the portion of said first beam scattered by said surface, said modulations produced by interference between radiation scattered by different points on said surface; and

said data processing means further includes means for deriving, from said characterization of the modulations, indicia of the roughness of said surface.

17. An apparatus as in claim 16 wherein:

said means for characterizing includes:

means for measuring the peak-to-peak amplitude of said modulations; and

means for measuring the angular displacement of said modulations; and said deriving means includes:

means for storing experimentally-obtained data comprising the peak-to-peak amplitudes and angular displacements of the modulations in coherent radiation scattered by a plurality of different predetermined surfaces, said modulations for each of said different surfaces produced by interference between radiation scattered by different points on said each surface; and

means for comparing said measured peak-to-peak amplitude and angular displacement data with said stored peak-to-peak amplitude and angular displacement data in order to approximate the roughness of said surface by the roughness of one of said predetermined surfaces.

18. An apparatus as in claim 13 wherein said surface roughness processing means includes:

means, coupled to said ranging detector means, for measuring the amplitude of said first wave interference pattern, said measured amplitude proportional to the intensity of the portion of said first beam scattered by said surface;

characterizing means, responsive to said detected amplitude, for characterizing modulations in the scattered radiation, said modulations produced by interference between portions of said first beam scattered by said different points on said surface; and

means for deriving, from said characterization of the modulations, indicia of the roughness of said surface.

19. An apparatus as in claim 18 wherein:

said means for characterizing includes:

means for measuring the peak-to-peak amplitude of said modulations; and

means for measuring the angular displacement of said modulations; and said deriving means includes:

means for storing experimentally-obtained data comprising the peak-to-peak amplitudes and angular displacements of the modulations in coherent radiation scattered by a plurality of different predetermined surfaces, said modulations for each of said different surfaces produced by interference between radiation scattered by different points on said each surface; and

means for comparing said measured peak-to-peak amplitude and angular displacement data with said stored peak-to-peak amplitude and angular displacement data in order to approximate the roughness of said surface by the roughness of one of said predetermined surfaces.

20. An apparatus as in claim 19 wherein said characterizing means includes means for scanning said first beam over said surface.

21. An apparatus as in claim 19 wherein said characterizing means includes means for changing the angle of incidence of said beam on said surface.

22. An apparatus for determining the roughness of a surface, comprising:

radiating means for directing a continuous beam of coherent radiation onto said surface, said radiating means including means for frequency sweep modulating the frequency of said radiation;

beam splitting means for splitting said radiation into a ranging beam and a reference beam;

ranging interferometer means optically coupled to said radiating means, for directing a first portion of said ranging beam along a path toward said surface, and for producing a first wave interference pattern between a second portion of the ranging beam travelling over a predetermined path and the first portion of said ranging beam scattered by said surface, and for providing an output signal proportional to the amplitude of the first wave interference pattern;

reference interferometer means for directing a first portion of said reference beam along a reference path of fixed, predetermined length, and for producing a second wave interference pattern between a second portion of said reference beam travelling over a second path an