Simultaneous triple aperture radar

• US 5,579,011 A
• Filed: 09/30/1982
• Issued: 11/26/1996
• Est. Priority Date: 11/02/1979
• Status: Expired due to Fees

• Current Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Original Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Inventors: Smrek, Walter J.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US06/436,747
• Time in Patent Office: 5,171 Days
• Field of Search: 343/7.7, 343/5 CM, 343/17.7, 342/113, 342/156
• US Class Current: 342/113
• CPC Class Codes: G01S 13/9023 combined with interferometric techniques
• CPC Class Codes: G01S 13/9029 specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time

Abstract

An improved radar system and technique are disclosed for use in detecting and tracking moving or stationary targets within the antenna field of view. Precise correction of doppler induced location errors is provided by the use of raw sensor data. Return signals are doppler processed, phase shifted and compared in a manner which preserves the angle of arrival of a moving target irrespective of the boresight direction. Stationary target return signals are constructively combined so as to augment the target signal gain independent of the antenna boresight direction.

Claims

1. In conjunction with an airborne synthetic aperture radar system having at least a first, second and third receiving antenna element, a method for detecting a moving target comprising the steps of:

a) positioning said first, second and third receiving antenna elements in a spaced relationship;

b) compensating the radar return signals received during a given aperture by said spaced first, second and third antenna elements to account for the motion of the radar bearing aircraft;

c) processing the motion compensated received radar return signals to form a first, second and third doppler processed signal, respectively;

d) phase shifting said first doppler processed signal by a predetermined amount;

e) phase shifting said second doppler processed signal by a predetermined amount;

f) differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

g) differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal; and

h) detecting using said first and second difference signals the presence or absence of a moving target.

2. In conjunction with an airborne synthetic aperture radar system having at least a first, second and third receiving antenna element, a method for detecting and tracking a moving target comprising the steps of:

a) positioning said first, second and third receiving antenna elements in a spaced relationship;

b) compensating the radar return signals received during a given aperture by said spaced first, second and third antenna elements to account for the motion of the radar bearing aircraft;

c) processing the motion compensated received radar return signals to form a first, second and third doppler processed signal, respectively;

d) phase shifting said first doppler processed signal by a predetermined amount;

e) phase shifting said second doppler processed signal by a predetermined amount;

f) differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

g) differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal;

h) detecting using said first and second difference signals the presence or absence of a moving target; and

i) determining when the presence of a moving target is detected the interferometric phase angle between said first and second difference signals, said interferometric phase angle being representative of the azimuth angle of the detected moving target.

3. In conjunction with an airborne synthetic aperture radar system having at least a first, second and third receiving antenna element, and a display, a method for detecting, tracking and displaying a moving target comprising the steps of:

a) positioning said first, second and third receiving antenna elements in a spaced relationship;

b) compensating the radar return signals received during a given aperture by said spaced first, second and third antenna elements to account for the motion of the radar bearing aircraft;

c) processing the motion compensated received radar return signals to form a first, second and third doppler processed signal, respectively;

d) phase shifting said first doppler processed signal by a predetermined amount;

e) phase shifting said second doppler processed signal by a predetermined amount;

f) differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

g) differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal;

h) detecting using said first and second difference signals the presence or absence of a moving target;

i) determining when the presence of a moving target is detected the interferometric phase angle between said first and second difference signals, said interferometric phase angle being representative of the azimuth angle of the detected moving target; and

j) positioning using said interferometric phase angle the detected moving target on said display.

4. In conjunction with an airborne synthetic aperture radar system having at least a first, second and third receiving antenna element, a method for detecting a moving target comprising the steps of:

a) positioning said first, second and third receiving antenna elements in a linear spaced relationship;

b) compensating the radar return signals received during a given aperture by said linearly spaced first, second and third antenna elements to account for the motion of the radar bearing aircraft;

c) processing the motion compensated received radar return signals to form a first, second and third doppler processed signal, respectively;

d) phase shifting said first doppler processed signal by a predetermined amount;

e) phase shifting said second doppler processed signal by a predetermined amount;

f) differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

g) differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal;

h) combining in a predefined manner said first and second difference signals to form a moving target return signal; and

i) detecting by comparing the magnitude of said moving target return signal to a predetermined moving target detection threshold the presence or absence of a moving target.

5. In conjunction with an airborne synthetic aperture radar system having at least a first, second and third receiving antenna element, a method for detecting and tracking a moving target comprising the steps of:

a) positioning said first, second and third receiving antenna elements in a linear spaced relationship;

b) compensating the radar return signals received during a given aperture by said linearly spaced first, second and third antenna elements to account for the motion of the radar bearing aircraft;

c) processing the motion compensated received radar return signals to form a first, second and third doppler processed signal, respectively;

d) phase shifting said first doppler processed signal by a predetermined amount;

e) phase shifting said second doppler processed signal by a predetermined amount;

f) differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

g) differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal;

h) combining in a predefined manner said first and second difference signals to form a moving target return signal;

i) detecting by comparing the magnitude of said moving target return signal to a predetermined moving target detection threshold the presence or absence of a moving target; and

j) determining when the presence of a moving target is detected the interferometric phase angle between said first and second difference signals, said interferometric phase angle being representative of the azimuth angle of the detected moving target.

6. In conjunction with an airborne synthetic aperture radar system having at least a first, second and third receiving antenna element, and a display, a method for detecting, tracking and displaying a moving target comprising the steps of:

a) positioning said first, second and third receiving antenna elements in a linear spaced relationship;

b) compensating the radar return signals received during a given aperture by said linearly spaced first, second and third antenna elements to account for the motion of the radar bearing aircraft;

c) processing the motion compensated received radar return signals to form a first, second and third doppler processed signal, respectively;

d) phase shifting said first doppler processed signal by a predetermined amount;

e) phase shifting said second doppler processed signal by a predetermined amount;

f) differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

g) differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal;

h) combining in a predefined manner said first and second difference signals to form a moving target return signal;

i) detecting by comparing the magnitude of said moving target return signal to a predetermined moving target detection threshold the presence or absence of a moving target;

j) determining when the presence of a moving target is detected the interferometric phase angle between said first and second difference signals, said interferometric phase angle being representative of the azimuth angle of the detected moving target;

k) determining using said interferometric phase angle the doppler filter index of the detected moving target;

l) determining using said interferometric phase angle and one of said first and second difference signals the signal strength of the detected moving target;

m) determining using said interferometric phase angle, one of said first and second difference signals, and one of said first, second and third doppler processed signals the signal strength of the stationary clutter underlying the detected moving target; and

n) displaying using said signal strength and said doppler filter index of the detected moving target, and said signal strength and known doppler filter index of the stationary clutter the detected moving target on said display.

7. A method as recited in claim 6 further including when the absence of a moving target is detected the steps of:

a) phase shifting said third doppler processed signal by a predetermined amount;

b) summing said phase shifted first doppler processed signal said second doppler processed signal and said phase shifted third doppler processed signal to form an enhanced stationary clutter return signal; and

c) displaying using the known doppler filter index of the stationary clutter and said enhanced stationary clutter return signal the stationary clutter on said display.

8. A method as recited in claim 6 further including the step of applying phase and amplitude corrections to the radar return signals received during a given aperture, the amount of said phase and amplitude corrections having been determined during the preceding aperture using said first and second difference signals, and said first and third doppler processed signals.

9. A method as recited in claim 8 wherein said signal strength of the detected moving target is determined using said interferometric phase angle and said first difference signal, and said signal strength of the stationary clutter underlying the detected moving target is determined using said interferometric phase angle, said first difference signal and said first doppler processed signal.

10. A method as recited in claim 8 wherein said signal strength of the detected moving target is determined using said interferometric phase angle and said first difference signal, and said signal strength of the stationary clutter underlying the detected moving target is determined using said interferometric phase angle, said second difference signal and said second doppler processed signal.

11. An airborne synthetic aperture radar system comprising:

a) first, second and third receiving antenna means positioned in a spaced relationship;

b) means for compensating the radar return signals received by said spaced first, second and third receiving antenna means to account for the motion of the radar bearing aircraft;

c) means for processing the motion compensated received radar return signals to form a first, second and third doppler processed signal, respectively;

d) means for phase shifting said first doppler processed signal by a predetermined amount;

e) means for phase shifting said second doppler processed signal by a predetermined amount;

f) means for differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

g) means for differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal; and

h) means for detecting using said first and second difference signals the presence or absence of a moving target.

12. An airborne synthetic aperture radar system as recited in claim 11 including means for determining when the presence of a moving target is detected the interferometric phase angle between said first and second difference signals, said interferometric phase angle being representative of the azimuth angle of the detected moving target.

13. An airborne synthetic aperture radar system as recited in claim 12 including means for positioning using said interferometric phase angle the detected moving target on a display.

14. An airborne synthetic aperture radar system comprising:

a) first, second and third receiving antenna means positioned in a linear spaced relationship;

b) means for compensating the radar return signals received by said linearly spaced first, second and third receiving antenna means to account for the motion of the radar bearing aircraft;

c) receiving and doppler processing means operatively connected to said linearly spaced first, second and third receiving antenna means, and to said motion compensating means, said receiving and doppler processing means including means for forming a first, second and third doppler processed signal, respectively;

d) moving target detecting means operatively connected to said receiving and doppler processing means, said moving target detecting means including;

1) means for phase shifting said first doppler processed signal by a predetermined amount;

2) means for phase shifting said second doppler processed signal by a predetermined amount;

3) means for differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

4) means for differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal; and

5) means for detecting using said first and second difference signals the presence or absence of a moving target.

15. An airborne synthetic aperture radar system as recited in claim 14 including moving target processing means operatively connected to said moving target detecting means, said moving target processing means including means for determining when the presence of a moving target is detected the interferometric phase angle between said first and second difference signals, said interferometric phase angle being representative of the azimuth angle of the detected moving target.

16. An airborne synthetic aperture radar system as recited in claim 15 wherein said moving target processing means further includes means for determining the doppler filter index of the detected moving target, and means for determining the signal strength of the detected moving target.

17. An airborne synthetic aperture radar system as recited in claim 16 including:

a) fixed target processing means operatively connected to said receiving and doppler processing means, said moving target detecting means and said moving target processing means, said fixed target processing means including means for determining the signal strength of the stationary clutter underlying the detected moving target; and

b) display and target cursor processing means operatively connected to said moving target processing means and said fixed target processing means, said display and target cursor processing means including means for displaying the detected moving target and the underlying stationary clutter.

18. An airborne synthetic aperture radar system as recited in claim 17 wherein said fixed target processing means further includes means for enhancing when the absence of a moving target is detected the stationary clutter, said stationary clutter enhancing means including:

a) means for phase shifting said third doppler processed signal by a predetermined amount; and

b) means for summing said phase shifted first doppler processed signal, said second doppler processed signal and said phase shifted third doppler processed signal to form an enhanced stationary clutter return signal, said signal being utilized to enhance in the absence of a detected moving target the displayed stationary clutter.

19. An airborne synthetic aperture radar system as recited in claim 18 wherein said receiving and doppler processing means further include multiplexing means for sampling in alternating pairs the radar return signals received by said linearly spaced first, second and third receiving antenna means.

20. An airborne triple synthetic aperture radar system comprising:

a) first, second and third receiving antenna means positioned in a linear spaced relationship;

b) first, second and third receiving means operatively connected to and responsive to the radar return signals received by said linearly spaced first, second and third receiving antenna means, respectively.;

c) means for compensating the received radar return signals to account for the motion of the radar bearing aircraft;

d) first, second and third doppler processing means operatively connected and responsive to said first, second and third receiving means, respectively, and to said motion compensating means, said first, second and third doppler processing means including means for forming a first, second and third doppler processed signal, respectively;

e) moving target detecting means operatively connected and responsive to said first, second and third doppler processing means, said moving target detecting means including;

1) means for phase shifting said first doppler processed signal by a predetermined amount;

2) means for phase shifting said second doppler processed signal by a predetermined amount;

3) means for differencing said phase shifted first doppler processed signal and said second doppler processed signal to form a first difference signal;

4) means for differencing said phase shifted second doppler processed signal and said third doppler processed signal to form a second difference signal;

5) means for combining said first and second difference signals to form a moving target return signal; and

6) means for comparing the magnitude of said moving target return signal to a predetermined moving target detection threshold to detect the presence or absence of a moving target;

f) moving target processing means operatively connected and responsive to said moving target detecting means, said moving target processing means including;

1) means operative when the presence of a moving target is detected for determining the interferometric phase angle between said first and second difference signals;

2) means for determining using said interferometric phase angle the doppler filter index of the detected moving target; and

3) means for determining using said interferometric phase angle and one of said first and second difference signals the signal strength of the detected moving target;

g) fixed target processing means operatively connected and responsive to said first, second and third doppler processing means, said moving target detecting means, and said moving target processing means, said fixed target processing means including means for determining using said interferometric phase angle, one of said first and second difference signals, and one of said first, second and third doppler processed signals the signal strength of the stationary clutter underlying the detected moving target; and

h) display and target cursor processing means operatively connected and responsive to said moving target processing means and said fixed target processing means, said display and target cursor processing means including means for displaying using said signal strength and said doppler filter index of the detected moving target, and said signal strength and known doppler filter index of the stationary clutter the detected moving target and the underlying stationary clutter.

21. An airborne triple synthetic aperture radar system as recited in claim 20 wherein said fixed target processing means further include means operative when the absence of a moving target is detected for enhancing the stationary clutter, said stationary clutter enhancing means including:

a) means for phase shifting said third doppler processed signal by a predetermined amount; and

b) means for summing said phase shifted first doppler processed signal, said second doppler processed signal and said phase shifted third doppler processed signal to form an enhanced stationary clutter return signal, said signal being utilized to enhance in the absence of a detected moving target the displayed stationary clutter.

22. An airborne triple synthetic aperture radar system as recited in claim 21 including means for applying phase and amplitude corrections to the received radar return signals.

23. An airborne triple synthetic aperture radar system as recited in claim 22 wherein the amount of said phase and amplitude corrections being determined during the preceding aperture using said first and second difference signals, and said first and third doppler processed signals.