Range/azimuth/elevation ship imaging for ordnance control

• US 4,546,355 A
• Filed: 06/17/1982
• Issued: 10/08/1985
• Est. Priority Date: 06/17/1982
• Status: Expired due to Fees

• Current Assignee: Grumman Aerospace Corporation Bethpage NY 11714
• Original Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Inventors: Boles, Sol
• Primary Examiner(s): Tubbesing, T. H.
• Assistant Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US06/389,369
• Time in Patent Office: 1,209 Days
• Field of Search: 343/5 CM, 343/7 G, 343/10, 343/11 R, 343/17, 343/7 ED, 364/516, 364/517
• US Class Current: 342/179
• CPC Class Codes: G01S 13/66 Radar-tracking systems; Analogous systems
• CPC Class Codes: G01S 13/9092 combined with monopulse techniques

Abstract

Capability is provided for producing 3 scaled high resolution orthogonal image projections on a CRT of a ship under the influence of translational as well as rotational motions arising from sea state conditions, for the purpose of ship target identification and classification, and the subsequent carrying out of stand-off command weapon guidance to a designated resolution cell of the ship from an airborne platform. Doppler processed interferometric azimuth and elevation angle measurements of the ship scatterers derived from a coherent synthetic aperture radar are combined in a weighted multivariate regression fit using digital signal processing techniques to provide measures of ship translational and rotational motions essential to providing focussed high resolution imagery and precision standoff weapon delivery to the designated ship target resolution cell. The invention also provides a capability for scaling the cross-range (doppler) dimension of Inverse SAR Profile Imagery.

Claims

1. In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a display, a method for forming high resolution synthetic aperture radar imagery of a ship target under the influence of sea state conditions comprising the steps of:

(a) processing the received signals from the scatterers comprising the ship target to obtain estimates of (1) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (2) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship;

(b) determining from the estimated doppler producing velocities the values of predetermined system parameters to be used predictively in the succeeding integration interval in forming the high resolution image of the ship target; and

(c) displaying the formed imagery of the ship target including a range/azimuth projection, an azimuth/elevation profile projection, and a range/elevation profile projection.

2. In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a display, a method for forming high resolution synthetic aperture radar imagery of a ship target under the influence of sea state conditions comprising the steps of:

(a) processing the received signals from the scatterers comprising the ship target to obtain estimates of (1) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (2) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship;

(b) determining from the estimated doppler producing velocities the values of predetermined system parameters to be used predictively in the succeeding integration interval in forming the high resolution imagery of the ship;

(c) displaying the formed imagery of the ship target including a range/azimuth projection, an azimuth/elevation profile projection, and a range/elevation profile projection; and

(d) forming and displaying an inverse synthetic aperture radar profile image projection of the ship target.

3. In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a display, a method for forming and displaying high resolution synthetic aperture radar imagery of a ship target under the influence of sea state conditions comprising the steps of:

(a) compensating using an estimate of the net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship for phase variations in the received signals from the scatterers comprising the ship target resulting from the respective motions of the radar bearing aircraft and the ship;

(b) processing in conjunction with azimuth and elevation angle interferometric techniques the compensated received signals to obtain estimates of (1) the error in the estimated net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (3) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight to the center of rotation tracking point of the ship;

(c) determining from the estimated cross line-of-sight relative velocity and the estimated orthogonal velocity the values of predetermined system parameters to be used predictively in the succeeding integration interval in forming the high resolution imagery of the ship target; and

(d) displaying the formed imagery of the ship target.

4. A method as recited in claim 3 wherein the step of processing the compensated received signals includes:

(a) measuring interferometrically the azimuth and elevation angles of the received signal in each doppler filter in each range bin; and

(b) obtaining from predefined characteristics derived from a weighted multivariate regression fit to the doppler processed azimuth and elevation angle measurement data the estimates of (1) the error in the estimated net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (3) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship.

5. A method as recited in claim 4 wherein the displayed imagery of the ship target includes a range/azimuth projection, an azimuth/elevation profile projection, and a range/elevation profile projection.

6. A method as recited in claim 5 including the further steps of forming and displaying an inverse synthetic aperture radar profile image projection of the ship target.

7. A method as recited in claim 6 including the further step of scaling the cross-range dimension of the displayed inverse synthetic aperture radar profile image projection of the ship target.

8. A method as recited in claim 7 including the further step of converting the displayed scaled inverse synthetic aperture radar profile image projection of the ship target to a stretched inverse synthetic aperture radar profile image projection.

9. In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a display, a method for forming and displaying high resolution synthetic aperture radar imagery of a ship target under the influence of sea state conditions comprising the steps of:

(a) steering the pointing of the interferometer antenna boresight to provide radar illumination of the ship target;

(b) controlling the range sampling timing so that corresponding samples from pulse-to-pulse over the integration interval correspond to the same range increment of the ship target;

(c) compensating using an estimate of the net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship for phase variations in the received signals from the scatterers comprising the ship target resulting from the respective motions of the radar bearing aircraft and the ship;

(d) measuring interferometrically the azimuth and elevation angles of the compensated received signal in each doppler filter in each range bin;

(e) obtaining from selected regression constants derived from a weighted least squares multivariate regression fit to the doppler processed azimuth and elevation angle measurement data estimates of (1) the error in the estimated net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (3) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship;

(f) determining from the estimated cross line-of-sight relative velocity and the estimated orthogonal velocity the values of predetermined system parameters to be used predictively in the succeeding integration interval in forming the high resolution imagery of the ship target; and

(g) displaying the formed imagery including a range/azimuth projection, an azimuth/elevation profile projection, and a range/elevation profile projection of the ship target.

10. A method as recited in claim 9 including the further steps of cursoring a designated resolution cell of the displayed imagery of the ship target;

and tracking from aperture to aperture the range and interferometric azimuth angle of the designated resolution target cell.

11. A method as recited in claim 10 including the further step of applying to the cursor location on an aperture to aperture basis a tracking correction to compensate for the rotation of the ship about an axis orthogonal to both the horizontal ship rotational axis and the radar line-of-sight to the center of rotation tracking point of the ship.

12. A method as recited in claim 11 including the further steps of obtaining and utilizing smoothed elevation locational values in forming the displayed azimuth/elevation profile and range/elevation profile image projections of the ship target.

13. A method as recited in claim 12 including the further steps of

(a) smoothing using the doppler processed azimuth and elevation angle measurement data obtained over multiple apertures the estimates obtained for (1) the error in the estimated net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (3) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship;

(b) determining from the smoothed estimated cross line-of-sight relative velocity and the smoothed estimated orthogonal velocity the values of the predetermined system parameters including synthetic aperture radar integration time and pulse repetition frequency and doppler filter bandwidths and spacings to be used predictively in the succeeding integration interval in forming the high resolution imagery of the ship target; and

(c) displaying the formed imagery of the ship target.

14. A method as recited in claim 13 including the further steps of forming and displaying an inverse synthetic aperture radar profile image projection of the ship target.

15. A method as recited in claim 14 including the further step of scaling the cross-range dimension of the displayed inverse synthetic aperture radar profile image projection of the ship target.

16. A method as recited in claim 15 including the further step of converting the displayed scaled inverse synthetic aperture radar profile image projection of the ship target to a stretched inverse synthetic aperture radar profile image projection.

17. A method as recited in claim 16 including the further steps of:

(a) smoothing using the doppler processed azimuth and elevation angle measurement data obtained over multiple apertures the estimate obtained for (1) the error in the estimated net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (3) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship;

(b) determining from the smoothed estimated cross line-of-sight relative velocity and the smoothed estimated orthogonal velocity the values of the predetermined system parameters including synthetic aperture radar integration time and pulse repetition frequency and doppler filter bandwidths and spacings to be used predictively in the succeeding integration interval in forming the high resolution imagery of the ship target; and

(c) displaying the formed imagery of the ship target.

18. In combination with an airborne synthetic aperture radar system including a multiple section interferometer antenna operatively connected to the input to a two way channel receiver and doppler processing system, and a display operatively connected to the output of said two channel receiver and doppler processing system, image signal processing means for forming and displaying high resolution synthetic aperture radar imagery of a ship target under the influence of sea state conditions comprising:

(a) means for obtaining from a weighted multivariate regression fit to the doppler processed interferometric azimuth and elevation angle measurement data the estimates of (1) the error in the estimated net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (3) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship, and smoothing using velocities derived from the regression solutions obtained over mulitple apertures smoothed estimates for (1) the error in the net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, and (3) the net doppler producing velocity in the direction orthogonal to the cross line-of-sight relative velocity and the radar line-of-sight to the center of rotation tracking point of the ship, and for determining from the smoothed estimated cross line-of-sight relative velocity and the smoothed estimated orthogonal velocity the values of the predetermined system parameters including synthetic aperture radar integration time and pulse repetition frequency and doppler filter bandwidths and spacings to be used predictively in the succeeding integration interval in forming the high resolution imagery of the ship target;

(b) means for compensating using a smoothed estimate of the net doppler producing line-of-sight velocity of the radar bearing aircraft relative to the ship for phase variations in the received signals from the scatterers comprising the ship target resulting from the respective line-of-sight motions of the radar bearing aircraft and the ship;

(c) means for forming and displaying scaled range/azimuth, azimuth/elevation, and range/elevation projected images of the ship target, and obtaining and utilizing smoothed elevation locational values in forming the displayed azimuth/elevation and range/elevation image projections;

(d) means for forming and displaying an inverse synthetic aperture radar (ISAR) profile image projection of the ship target with scaled cross-range dimensions, and converting the scaled inversed synthetic aperture radar (ISAR) profile image projection of the ship target to a stretched ISAR profile image projection;

(e) means for cursoring a designated resolution cell of the displayed imagery of the ship target and for tracking from aperture to aperture the range and interferometrically determined azimuth of the designated resolution target cell, and applying to the cursor location on an aperture to aperture basis a tracking correction to compensate for the rotation of the ship about the axis orthogonal to both the horizontal ship rotational axis and the radar line-of-sight to the center of rotation tracking point of the ship;

(f) means for steering the pointing of the interferometer antenna boresight to provide optimum radar illumination of the ship target and image centering along the azimuth and elevation axis; and

(g) means for controlling the range sampling timing so that corresponding samples from pulse to pulse over the integration interval correspond to the same range increment of the ship target.