Range/azimuth angle ship imaging 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 with improved azimuth resolution a range/azimuth image 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 coherent integration interval in forming the range/azimuth image.

Claim 3

A method as recited in Claim 1 including the further step of displaying the formed range/azimuth image of the ship target on the range versus azimuth angle display.

Claim 4

A method as recited in Claim 2 including the further steps of cursoring a designated range/azimuth resolution cell of the displayed image of the ship target; and tracking from aperture to aperture the range and interferometric azimuth angle of the designated resolution target cell.

Claim 5

A method as recited in Claim 3 including the further step of compensating for phase variations in the received signals due to the respective motions of the radar bearing aircraft and the ship.

Claim 6

A method as recited in Claim 4 including the further step of steering the pointing of the interferometer antenna boresight to provide radar illumination of the ship target.

Claim 7

A method as recited in Claim 5 including the further step of controlling the range sampling timing so that corresponding range samples from pulse-to-pulse over the coherent integration interval correspond to the same range increment of the ship target.

Claim 8

A method as recited in Claim 6 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 aircraft horizontal cross line-of-sight velocity and the radar line-of-sight to the centre of rotation tracking point of the ship.

Claim 9

A method as recited in Claim 7 wherein the step of processing the compensated received signals includes: a) measuring interferometrically the compensated received signals for each doppler filter in each range bin; b) plotting as interferometer azimuth angle versus filter doppler frequency the measured data for each doppler filter in each range bin; c) performing a straight line fit to the plotted data points of the azimuth angle/doppler distribution for each range bin; d) determining the slope of the straight line fit to the azimuth angle/doppler distribution for each range bin; e) averaging the slope values determined over all range bins; and f) obtaining from the averaged slope value an estimate of the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship.

Claim 10

A method as recited in Claim 8 including the further steps of excluding any data points located outside of a prescribed threshold band about the straight line fit formed from all available data points of the azimuth angle/doppler distribution for each range bin; and refitting to the data after such exclusion.

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 with improved azimuth resolution a scaled range/azimuth image 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 coherent integration interval correspond to the same range increment of the ship target; c) compensating for phase variations in the received signals due to the respective motions of the radar bearing aircraft and the ship; d) measuring interferometrically the compensated received signals for each doppler filter in each range bin; e) plotting as interferometer azimuth angle versus filter doppler frequency the measured data for each doppler filter in each range bin; f) performing a weighted least squares linear regression straight line fit to the plotted data points of the azimuth angle/doppler distribution for each range bin; g) determining the slope of the straight line fit to the azimuth angle/doppler distribution for each range bin; h) averaging the slope values determined over all range bins; and i) determining from the averaged slope value the values of predetermined system parameters including synthetic aperture radar integration time and doppler filter bandwidths and spacings to be used predictively in the succeeding coherent integration interval in forming the range/azimuth image.

Claim 12

In conjunction with an airborne synthetic aperture radar system having an interferometer antenna and a range versus azimuth angle display, a method for forming with improved azimuth resolution a scaled range/azimuth image 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 coherent integration interval correspond to the same range increment of the ship target; c) compensating for phase variations in the received signals due to the respective motions of the radar bearing aircraft and the ship; d) measuring interferometrically the compensated received signals for each doppler filter in each range bin; e) plotting as interferometer azimuth angle versus filter doppler frequency the measured data for each doppler filter in each range bin; f) performing a weighted least squares linear regression straight line fit to the plotted data points of the azimuth angle/doppler distribution for each range bin; g) determining the slope of the straight line fit to the azimuth angle/doppler distribution for each range bin; h) averaging the slope values determined over all range bins; and i) determining from the averaged slope value the values of predetermined system parameters including synthetic aperture radar integration time and doppler filter bandwidths and spacings to be used predictively in the succeeding coherent integration interval in forming the range/azimuth image.

Claim 13

A method as recited in Claim 10 including the further steps of: a) displaying the formed range/azimuth image of the ship target on the range versus azimuth angle display; b) cursoring a designated range/azimuth resolution cell of the displayed image of the ship target; and c) tracking from aperture to aperture the desic- nated resolution cell of the ship target.

Claim 14

A method as recited in Claim 11 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 aircraft horizontal cross line-of-sight velocity and the radar line-of-sight to the center of rotation tracking point of the ship.

Claim 15

A method as recited in Claim 12 including the further steps of excluding any data points located outside of a prescribed threshold band about the least squares fit formed from all available data points of the azimuth angle/doppler distribution for each range bin; and refitting to the data after such exclusion.

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 with improved azimuth resolution a range/azimuth image 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 coherent integration interval in forming the range/azimuth 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 with improved azimuth resolution a range/azimuth image 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 coherent integration interval in forming the range/azimuth image.

Claim 18

A combination as recited in Claim 14 wherein the image signal processing means further include means for displaying the formed range/azimuth image of the ship target on the range versus azimuth angle display.

Claim 19

A bombination as recited in Claim 15 wherein the image signal processing means further include means for cursoring a designated range/azimuth resolution cell of the displayed image of the ship target; and means for tracking from aperture to aperture the range interferometric azimuth angle of the designated resolution target cell.

Claim 20

A combination as recited in Claim 16 wherein the image signal processing means further include means for compensating for phase variations in the received signals due to the respective motions of the radar bearing aircraft and the ship.

Claim 21

A combination as recited in Claim 17 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 22

A combination as recited in Claim 18 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 coherent integration interval correspond to the same range increment of the ship target.

Claim 23

A combination as recited in Claim 19 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 aircraft horizontal cross line-of-sight velocity and the radar line-of-sight to the center of rotation tracking point of the ship.

Claim 24

A combination as recited in Claim 20 wherein the processing means includes: a) means for measuring interferometrically the compensated received signals for each doppler filter in each range bin; b) means for plotting as interferometer azimuth angle versus filter doppler frequency the measured data for each doppler filter in each range bin; c) means for performing a straight line fit to the plotted data points of the azimuth angle/doppler distribution for each range bin; d) means for determining the slope of the straight line fit to the azimuth angle/doppler distribution for each range bin; e) means for averaging the slope values determined over all range bins; and f) means for obtaining from the averaged slope value an estimate of the net doppler producing cross line-of-sight velocity of the radar bearing aircraft relative to the ship.

Claim 25

A combination as recited in Claim 21 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 azimuth angle/doppler distribution for each range bin; and means for refitting to the data after such exclusion.

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 with improved azimuth resolution a scaled range/azimuth image 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 coherent integration interval correspond to the same range increment of the ship target; c) means for compensating for phase variations in the received signals due to the respective motions of the radar bearing aircraft and the ship; d) means for measuring interferometrically the compensated received signals for each doppler filter in each range bin; e) means for plotting as interferometer azimuth angle versus filter doppler frequency the measured data for each doppler filter in each range bin; f) means for performing a weighted least squares linear regression straight line fit to the plotted data points of the azimuth angle/doppler distribution for each range bin; g) means for determining the slope of the straight line fit to the azimuth angle/doppler distribution for each range bin; h) means for averaging the slope values determined over all range bins; and i) means for determining from the averaged slope value the values of predetermined system parameters Including synthetic aperture radar integration time and doppler filter bandwidths and spacings to be used predictively in the succeeding coherent integration intervals in forming the range/azimuth image.

Claim 27

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 with improved azimuth resolution a scaled range/azimuth image 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 coherent integration interval correspond to the same range increment of the ship target; c) means for compensating for phase variations in the received signals due to the respective motions of the radar bearing aircraft and the ship; d) means for measuring interferometrically the compensated received signals for each doppler filter in each range bin; e) means for plotting as interferometer azimuth angle versus filter doppler frequency the measured data for each doppler filter in each range bin; f) means for performing a weighted least squares linear regression straight line fit to the plotted data points of the azimuth angle/doppler distribution for each range bin; g) means for determining the slope of the straight line fit to the azimuth angle/doppler distribution for each range bin; h) means for averaging the slope values determined over all range bins; and i) means for determining from the averaged slope value the values of predetermined system parameters Including synthetic aperture radar integration time and doppler filter bandwidths and spacings to be used predictively in the succeeding coherent integration intervals in forming the range/azimuth image.

Claim 28

A combination as recited in Claim 23 wherein the image signal processing means further include: a) means for displaying the formed range/azimuth image of the ship target on the range versus azimuth angle display; b) means for cursoring.a designated range/azimuth resolution cell of the displayed image of the ship target; c) means for tracking from aperture to aperture the designated resolution cell of the ship target; and d) 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 an axis orthogonal to both the aircraft horizontal cross line-of-sight velocity and the radar line-of-sight to the centre of rotation tracking point of the ship.

Claim 29

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