Range/Doppler ship imagine for ordnance control

Claim 2

In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, a method for forming a range/doppler image having improved azimuth resolution 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 an estimate of the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship; and b) determining from the estimated cross line-of-sight relative velocity the values of predetermined system parameters to be used predictively in the succeeding integration interval in forming the range/doppler image.

Claim 3

A method as recited in claim 1 including the further step of displaying in a range versus azimuth angle coordinate frame the formed range/doppler image of the ship target.

Claim 4

A method as recited in claim 1 or 2 including the further steps of removing the isodop distortion in the formed range/doppler image and centering the displayed range/doppler image of the ship target.

Claim 10

In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, a method for forming and displaying a range/doppler image having improved azimuth resolution 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 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 angle of the compensated received signal in each doppler filter in each range bin; e) plotting measured interferometric azimuth angle as a function of a predefined doppler cell index and a predefined range cell index for all range and doppler cell indices; f) fitting in conjunction with a weighted least squares linear regression technique straight lines to the plotted doppler/azimuth angle distributions for each of the range bins; g) obtaining from selected regression constants derived from the family of fitted straight lines estimates of (1) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing velocity in the direction orthogonal to the relative cross line-of-sight velocity to the center of rotation tracking point of the ship, and (3) the error in the line of sight velocity; h) determining from the measured cross line-of-sight relative velocity the values of 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 range/doppler image; i) displaying in a range versus azimuth angle coordinate frame the formed range/doppler image of the ship target; j) removing using the estimated orthogonal velocity,,the isodop distortion in the formed range/ doppler image of the ship target; and k) centering using the estimated error in the line-of-sight velocity, the displayed range/doppler image of the ship target.

Claim 11

In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, a method for forming and displaying a range/doppler image having improved azimuth resolution 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 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 angle of the compensated received signal in each doppler filter in each range bin; e) plotting measured interferometric azimuth angle as a function of a predefined doppler cell index and a predefined range cell index for all range and doppler cell indices; f) fitting in conjunction with a weighted least squares linear regression technique straight lines to the plotted doppler/azimuth angle distributions for each of the range bins; g) obtaining from selected regression constants derived from the family of fitted straight lines estimates of (1) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing velocity in the direction orthogonal to the relative cross line-of-sight velocity to the center of rotation tracking point of the ship, and (3) the error in the line of sight velocity; h) determining from the measured cross line-of-sight relative velocity the values of 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 range/doppler image; i) displaying in a range versus azimuth angle coordinate frame the formed range/doppler image of the ship target; j) removing using the estimated orthogonal velocity,,the isodop distortion in the formed range/ doppler image of the ship target; and k) centering using the estimated error in the line-of-sight velocity, the displayed range/doppler image of the ship target.

Claim 13

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 the axis orthogonal to both the relative cross line-of-sight velocity and the radar line-of-sight to the center of rotation tracking point of the ship.

Claim 16

In combination with an airborne synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, image signal processing means for forming a range/doppler image having improved azimuth resolution of a ship target under the influence of sea state conditions comprising: a) means for processing the received signals from the scatterers comprising the ship target to obtain an estimate of the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship; and b) means for determining from the estimated cross line-of-sight relative velocity the values of predetermined system parameters to be used predictively in the succeeding integration interval in forming the range/doppler image.

Claim 17

In combination with an airborne synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, image signal processing means for forming a range/doppler image having improved azimuth resolution of a ship target under the influence of sea state conditions comprising: a) means for processing the received signals from the scatterers comprising the ship target to obtain an estimate of the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship; and b) means for determining from the estimated cross line-of-sight relative velocity the values of predetermined system parameters to be used predictively in the succeeding integration interval in forming the range/doppler image.

Claim 18

A combination as recited in claim 14 wherein the image signal processing means further include means for displaying in a range versus azimuth angle coordinate frame the formed range/doppler image of the ship target.

Claim 19

A combination as recited in claim 14 or 15 wherein the image signal processing means further include means for removing the isodop distortion in the formed range/doppler image; and means for centering the displayed range/doppler iamge of the ship target.

Claim 20

A combination as recited in any of claims 14 to 16 wherein the image signal processing means further include means for steering the pointing of the interferometer antenna boresight to provide radar illumination of the ship target.

Claim 21

A combination as recited in any of claims 14 to 17 wherein the image signal processing means further include means for controlling the range sampling timing so that corresponding range samples from pulse-to-pulse over the integration interval correspond to the same range increment of the ship target.

Claim 22

A combination as recited in any of claims 14 to 18 wherein the image signal processing means further include means for 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 relative cross line-of-sight velocity and the radar line-of-sight to the center of rotation tracking point of the ship target.

Claim 23

A combination as recited in any of claims 14 to 19 wherein the processing means include: a) means for measuring interferometrically the azimuth angle of the received signal in each dopper filter in each range bin; b) means for plotting measured interferometric azimuth angle as a function of a predefined doppler cell index and a predefined range cell index for all range and doppler cell indices; c) means for fitting straight lines to the plotted'doppler/azimuth angle distributions for each of the range bins; and d) means for obtaining from predefined characteristics derived from the family of fitted straight lines an estimate of the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship.

Claim 24

A combination as recited in any of claims 14 to 20 wherein the image signal processing means further include: a) means for obtaining from predefined characteristics derived from the family of fitted straight lines an estimate of (1) the net doppler producing velocity in the direction orthogonal to the relative cross line-of-sight velocity and the radar line of sight to the center of rotation tracking point of the ship; and (2) the error in the line-of-sight velocity; b) means for removing using the estimated orthogonal velocity the isodop distortion in the formed range/doppler image of the ship target; and c) means for centering using the estimated error in the line-of-sight velocity the displayed range/ doppler image of the ship target.

Claim 25

In combination with an airborne synthetic aperture radar system including a two section interferometer antenna operatively connected to the input to a two channel receiver and doppler processing system, and a display of range versus azimuth angle operatively connected to the output of said two channel receiver and doppler processing system, image signal processing means for forming and displaying a range/ doppler image having improved azimuth resolution of a ship target under the influence of sea state conditions comprising: a) means for steering the pointing of the interferometer antenna boresight to provide radar illumination of the ship target; b) 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; c) means for compensating 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) means for measuring interferometrically the azimuth angle of the compensated received signal in each doppler filter in each range bin; e) means for plotting measured interferometric azimuth angle as a function of a predefined doppler cell index and a predefined range cell index for all range and doppler cell indices; f) means for fitting in conjunction with a weighted least squares linear regression technique straight lines to the plotted doppler/azimuth angle distributions for each of the range bins; g) means for obtaining from selected regression constants derived from the family of fitted straight lines estimates of (1) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing velocity in the direction orthogonal to the relative cross line-of-sight velocity and the radar line-of-sight to the center of rotation tracking point of the ship, and (3) the error in the line-of-sight velocity; h) means for determining from the estimated cross line-of-sight relative velocity the values of predetermined system paramaters 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 range/doppler image; i) means for displaying in a range versus azimuth angle coordinate frame the formed range/doppler image of the ship target; j) means for removing using the estimated orthogonal velocity the isodop distortion in the formed range/doppler image of ship target; and k) means for centering usingthe-eatimated error in the line-of-sight velocity the displayed range/ doppler image of the ship target.

Claim 26

In combination with an airborne synthetic aperture radar system including a two section interferometer antenna operatively connected to the input to a two channel receiver and doppler processing system, and a display of range versus azimuth angle operatively connected to the output of said two channel receiver and doppler processing system, image signal processing means for forming and displaying a range/ doppler image having improved azimuth resolution of a ship target under the influence of sea state conditions comprising: a) means for steering the pointing of the interferometer antenna boresight to provide radar illumination of the ship target; b) 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; c) means for compensating 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) means for measuring interferometrically the azimuth angle of the compensated received signal in each doppler filter in each range bin; e) means for plotting measured interferometric azimuth angle as a function of a predefined doppler cell index and a predefined range cell index for all range and doppler cell indices; f) means for fitting in conjunction with a weighted least squares linear regression technique straight lines to the plotted doppler/azimuth angle distributions for each of the range bins; g) means for obtaining from selected regression constants derived from the family of fitted straight lines estimates of (1) the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship, (2) the net doppler producing velocity in the direction orthogonal to the relative cross line-of-sight velocity and the radar line-of-sight to the center of rotation tracking point of the ship, and (3) the error in the line-of-sight velocity; h) means for determining from the estimated cross line-of-sight relative velocity the values of predetermined system paramaters 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 range/doppler image; i) means for displaying in a range versus azimuth angle coordinate frame the formed range/doppler image of the ship target; j) means for removing using the estimated orthogonal velocity the isodop distortion in the formed range/doppler image of ship target; and k) means for centering usingthe-eatimated error in the line-of-sight velocity the displayed range/ doppler image of the ship target.

Claim 27

A combination as recited in any of claims 14 to 22 wherein the image signal processing means further include means for cursoring a designated range/doppler resolution cell of the displayed image of the ship target; and means for tracking from aperture to aperture the range and interferometric azimuth angle of the designated resolution target cell.

Claim 28

A combination as recited in claim 23 wherein the image signal processing means further include means for 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 relative cross line-of-sight velocity and the radar line-of-sight to the center of rotation tracking point of the ship.

Claim 29

A combination as recited in any of claims 14 to 24 wherein the image signal processing means further include means for excluding any data points located outside of a prescribed threshold band about the straight line fit formed from all available data points of the doppler/azimuth angle distribution for each range bin; and means for refitting to the data after such exclusion.

Claim 30

A combination as recited in any of claims 14 to 25 wherein the image signal processing means further include means for tracking utilizing the range/doppler/ azimuth angle measurement data obtained from all the scatterers comprising the ship target with substantially improved azimuth resolution the designated range/doppler resolution cell.