Frequency modulated lasar radar

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.

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 and said first portion of said reference beam travelling over said reference path;
• means for varying the angle of incidence of said first portion of said ranging beam on said surface;
• detecting means for detecting the intensity of said radiation scattered by said surface for a plurality of different ones of said angles of incidence, said intensity corresponding to said output signal of said ranging interferometer means;
• and
• processing means for processing said detected intensities and said first and second wave interference patterns to produce indicia of surface roughness.

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 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 and said first portion of said reference beam travelling over said reference path;
• detecting means for detecting the intensity of the radiation scattered by said surface, said intensity corresponding to the output signal from said ranging means;
• characterizing means, responsive to said detected intensity, for characterizing modulations in the scattered radiation, said modulations produced by interference between radiation, scattered by different points on said surface;
• and
• means for deriving from said characterization of the modulations and said first and second wave interference patterns, indicia of the roughness of said surface.

A method for measuring the distance to an arbitrary target, comprising the steps of:

• (1) producing a beam of coherent radiation;
• (2) frequency sweep modulating the frequency of said radiation;
• (3) dividing the beam into a ranging beam and a reference beam;
• (4) directing a first portion of said ranging beam along a path toward said target, and focusing said ranging beam on said target;
• (5) producing a first wave interference pattern between the first portion of said ranging beam scattered by said target and a second portion of said ranging beam traveling over another path, and track filtering said first wave interference pattern to reduce noise therein;
• (6) directing a first portion of said reference beam along a reference path of a first, predetermined known length;
• (7) producing a second wave interference pattern between the first portion of said reference beam over said reference path and a second portion of said reference beam traveling over another path
• (8) processing said first and second wave interference patterns to determine the distance to said target;
• and characterizing the roughness of said scattering surface of said target.

A method for determining the roughness of a surface, comprising the steps of:

• directing a beam of coherent radiation onto said surface, the frequency of said radiation being frequency sweep modulated;
• splitting said radiation into ranging and reference beams;
• directing a first portion of said ranging beam along a path toward said surface;
• 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;
• providing an output signal proportional to the amplitude of said first wave interference pattern;
• directing a first portion of said reference beam along a path of fixed, predetermined length;
• producing a second wave interference pattern between a second portion of said reference beam travelling over a second path and said first portion of said reference beam travelling over said reference path;
• varying the angle of incidence of said first portion of said ranging beam on said surface;
• detecting the intensity of said radiation scattered by said surface for a plurality of different ones of said angles of incidence, said intensity corresponding to said output signal;
• and
• processing said detected intensities and said first and second wave interference patterns to produce indicia of surface roughness.

A method for determining the roughness of a surface, comprising the steps of:

• directing a beam of coherent radiation onto said surface, the frequency of said radiation being frequency sweep modulated;
• splitting said radiation into ranging and reference beams;
• directing a first portion of said ranging beam along a path toward said surface;
• 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;
• providing an output signal proportional to the amplitude of the first wave interference pattern;
• detecting the intensity of the radiation scattered by said surface, said intensity corresponding to said output signal;
• directing a first portion of said reference beam along a path of fixed, predetermined length;
• producing a second wave interference pattern between a second portion of said reference beam travelling over a second path and said first portion of said reference beam travelling over said reference path;
• characterizing modulations in the intensity of the scattered radiation, said modulations produced by interference between portions of said radiation scattered by different points on said surface;
• and
• deriving, from said characterization of the modulations and from said first and second wave interference patterns, indicia of roughness of said surface.