Optical doppler radar system using a conically scanned laser beam

• US 4,340,299 A
• Filed: 03/13/1980
• Issued: 07/20/1982
• Est. Priority Date: 03/13/1980
• Status: Expired due to Term

• Current Assignee: United Technologies Optical Systems, Inc. (Rtx Corporation)
• Original Assignee: United Technologies Corporation (Rtx Corporation)
• Inventors: Mongeon, Robert J.
• Primary Examiner(s): BUCZINSKI, STEPHEN C
• Application Number:
  US06/129,947
• Time in Patent Office: 859 Days
• Field of Search: 356/1, 356/4, 356/5, 356/28.5, 358/95, 358/96, 358/109, 343/5 CM
• US Class Current: 356/28.5
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems

Abstract

A homodyne laser of a first frequency is conically scanned on a surface from an elevated position and the beam is scattered by the surface. A return beam is formed from this scattered beam and is mixed with a single side band suppressed carrier laser beam at an offset frequency, producing an electrical signal whose frequency shifts from the offset frequency in proportion to the velocity relative to the surface. That shift is a function of the scan position and the direction of movement. Velocity components of the signal reflecting drift velocity and heading velocity are resolved from this signal by referencing it to the scan position at drift and heading positions. The signal component reflecting elevation velocity is resolved by removing those scan dependent components.

Claims

1. A method for generating indicia of movement relative to a surface at a position above the surface comprising the steps:

scanning a first laser beam and synchronously receiving, during the scan, the first laser beam scattered from the surface to produce a return laser beam,

generating a frequency difference electrical signal from the frequency difference between the return laser beam and the first laser beam after mixing it with a reference frequency,

generating movement signals that indicate electrical movement and horizontal movement in selected horizontal directions by splitting said frequency difference signal into its components that vary in proportion to movement in selected directions and that component which varies independently of the position of the scan, characterized by;

generating a scan position signal indicative of of the position of the scan from a reference position,

comparing the phase of said scan position signal with the phases of said frequency difference signals at quadrature phase angles the correspond to the quadrature angular positions of the scan to produce indicia of horizontal movements in selected directions resulting in signals proportional to the phase differences,

producing an indicia of elevational movement comprising a signal whose magnitude is proportional to the average level of the frequency difference signal.

2. A Doppler navigation system for generating indicia of movement relative to a surface at a position above the surface, said navigation system comprising:

a first laser for generating a first laser beam,

a laser beam scanning system for conically scanning the first laser beam on the surface and for producing a return laser beam by synchronously receiving, during the scan, the laser beam scattered from the surface,

means for generating a second laser beam at a frequency which is different than the frequency of said first laser beam and a reference frequency;

detector means for heterodyning said return beam and said second laser beam to produce a first electrical signal indicative of the difference between a frequency change of said return beam and said reference frequency,

a discriminator detector for providing a second electrical signal indicative of the frequency change of said return laser beam,

said scanning system including means for synchronously generating a scan position signal that is indicative of the position of the scan relative to a reference position,

vector resolving means comprising;

means for splitting said scan position signal into two quadrature components,

means for generating a first indicia of movement in one horizontal direction from the phase difference between one of said quadrature components and said second electrical signal,

means for generating a second indicia of movement in another horizontal direction from the phase difference between said second electrical signal and the second of said quadrature components, and

means for generating an indicia of elevational movement from the average level of the second electrical signal.

3. A Doppler navigation system according to claim 2, characterized in that:

said scan position generating means comprises an oscillator for producing a repetitive signal at the scan frequency and means for phase shifting a portion of said repetitive signal 90°

to produce one of said components.