Apparatus and method for producing three-dimensional images

• US 5,394,151 A
• Filed: 09/30/1993
• Issued: 02/28/1995
• Est. Priority Date: 09/30/1993
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Heidbreder, Glen R., Knaell, Kenneth K.
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US08/129,499
• Time in Patent Office: 516 Days
• Field of Search: 342/25
• US Class Current: 342/25.00F
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/9019 Auto-focussing of the SAR signals
• CPC Class Codes: G01S 13/904 SAR modes
• CPC Class Codes: G01S 13/9089 SAR having an irregular aperture
• CPC Class Codes: G01S 7/4021 of receivers

Abstract

An apparatus and method is capable of acquiring useful three-dimensional ar images from an aircraft which travels in a curvilinear path to generate only a sparsely filled synthetic array. A motion measurement unit outputs position measurements as the aircraft travels in the curvilinear path. The system includes a motion compensation and timing unit and a wave transmitter which outputs chirped radar signals. An antenna coupled to the wave generator sends the chirped radar signals to a region to be imaged and receives scattered chirped radar return signals from scatterers in the region. These scattered signals are coherently mixed to baseband and digitized before being input to a processor. The processor includes a range processing unit, a memory unit and an estimator. The range processor receives and Fourier transforms the digitized return signals to obtain range profiles. The estimator completes the image formation process by three-dimensional back projection of the range profiles. It also estimates the location and complex strengths of scatterers and uses these to generate a side lobe free image.

Claims

1. A system for generating three-dimensional radar image data from radar target return signals generated by aperture elements of a synthetic aperture radar on a vehicle moving along a path that is curvilinear with respect to said target, which system discriminates against spurious responses associated with the sparseness of the synthetic array, comprising in combination;

means for generating line of sight angle values from said curvilinear path to said target;

processor means for;

a) generating phase and amplitude values of scattering points from said radar return signals by Fourier transforming said radar return signals from said target to generate three-dimensional image data and identifying a highest peak of said three-dimensional image data as a scattering point of said target;

b) subtracting a Fourier transform of a weighted, shifted point spread function based on said line of sight angle values and element weights from said radar returned digital data to yield, as a result of said subtraction process, modified digital data; and

c) iteratively identifying highest peaks of three-dimensional image data as scattering points of said target; and

d) subtracting a Fourier transform of a weighted, shifted point spread function from said modified digital data to yield estimated scattering element positions and strengths from target scattering points in three dimensions.

2. A method for generating three-dimensional radar image data from radar target return signals generated by aperture elements of a synthetic aperture radar on a vehicle moving along a path that is curvilinear with respect to said target, which method discriminates against the spurious responses associated with the sparseness of the synthetic array, comprising the steps of;

generating line of sight angle values from said curvilinear path to said target;

generating phase and amplitude values of scattering points from said radar return signals by Fourier transforming said radar return signals from said target to generate three-dimensional image data;

identifying highest peaks of three-dimensional image data as scattering points of said target;

subtracting a Fourier transform of a weighted, shifted point spread function based on said line of sight angle values and element weights from radar returned digital data to yield, as a result of said subtraction process, modified digital data; and

iteratively identifying highest peaks of three-dimensional image data as scattering points of said target; and

subtracting a Fourier transform of a weighted, shifted point spread function from said modified digital data to yield estimated scattering element positions and strengths from target scattering points in three dimensions.

3. A system for generating three-dimensional radar image data from radar target return signals generated by aperture elements of a synthetic aperture radar on a vehicle moving along a path that is curvilinear with respect to said target, which system discriminates against spurious responses associated with the sparseness of the synthetic array, comprising in combination;

motion compensation and timing unit for receiving the motion information and for outputting a timing signal and a motion compensation signal in accordance with said motion information;

a wave transmitter coupled to said motion compensation and timing unit for receiving said timing signal and for repeatedly outputting chirped radar signals synchronized with said timing signal;

an antenna coupled to said wave transmitter for transmitting said chirped radar signals and receiving scattered chirped radar return signals as a result of said chirped radar signals;

antenna pointing controller coupled to said motion compensation and timing unit for receiving the motion information and for outputting antenna pointing commands in accordance with the motion information;

an antenna pointer connected to said antenna and coupled to said antenna pointing controller for receiving said antenna pointing commands and pointing said antenna in accordance with said pointing commands;

coherent receiver coupled to said motion compensation and timing unit and said antenna for receiving and mixing said scattered chirped radar return signals down to baseband return signals;

analog-to-digital converter coupled to said coherent receiver, said antenna pointing controller and said motion compensation and timing unit for receiving said baseband return signal, said timing signal and said motion compensation signal from said motion compensation and timing unit, digitizing said baseband return signal and outputting digitized return signals;

processor means for;

a) generating phase and amplitude values of scattering points from said radar return signals by Fourier transforming said radar return signals from said target to generate three-dimensional image data and identifying a highest peak of said three-dimensional image data as a scattering point of said target;

b) subtracting a Fourier transform of a weighted, shifted point spread function based on said line of sight angle values and element weights from said radar returned digital data to yield, as a result of said subtraction process, modified digital data;

c) iteratively identifying highest peaks of three-dimensional image data as scattering points of said target; and

d) subtracting a Fourier transform of a weighted, shifted point spread function from said modified digital data to yield estimated scattering element positions and strengths from target scattering points in three dimensions; and

squaring device for receiving and three dimensional image values and outputting display data which can be used to display a three dimensional image.