# US 12,111,394 B2 · Method and device for improved range tracking for inverse synthetic aperture radar

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- Number: US 12,111,394 B2
- Document ID: US12111394B2
- Status: Granted
- Kind: B2
- Application number: 17/326,412
- Filed: 2021-05-21
- Published: 2022-11-24
- Granted: 2024-10-08
- Earliest claimed: 2021-05-21
- Assignees: Kabushiki Kaisha Toshiba
- Applicants: Kabushiki Kaisha Toshiba
- Inventors: Seifallah Jardak
- Web page: https://patentgrep.com/patent/US12111394B2

## CPC

- G01S 13/9019: {Auto-focussing of the SAR signals}
- G01S 13/9064: {Inverse SAR [ISAR]}
- G01S 7/41: using analysis of echo signal for target characterisation; Target signature; Target cross-section
- G01S 13/58: Velocity or trajectory determination systems; Sense-of-movement determination systems
- G01S 13/9029: {specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time}
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

The present application presents various techniques for improving the performance of range tracking motion compensation method for high resolution radar imaging. Three improved techniques are described herein: improved cross-correlation alignment through updates to the reference range profile to follow the target's changing illumination angle; improved cross-correlation alignment through local peak boosting; and, improved polynomial smoothing through subdivision into multiple windows.

## Claims

### Claim 1

A computer implemented method comprising:
obtaining a plurality of range profiles each representing a plurality of return measurements from a corresponding pulse;
selecting one or more sets of range profiles from the plurality of range profiles;
for a selected set of range profiles, selecting a reference range profile from the plurality of range profiles;
for a selected reference range profile, applying motion compensation to a corresponding set of range profiles based on the reference range profile, wherein applying motion compensation comprises:
for a range profile of the selected set of range profiles in the corresponding set of range profiles, correlating the range profile with the reference range profile to produce a corresponding correlation distribution;
determining for a first correlation distribution of the correlation distributions a range shift corresponding to a maximum correlation in the correlation distribution, the maximum correlation indicating correlation values that are within a predefined threshold of a peak value in the correlation distribution;
for a subsequent correlation distribution from the correlation distributions:
determining a region of range shifts around a determined range shift corresponding to a maximum correlation of a previous correlation distribution;
increasing correlation values for the correlation distribution across the region of range shifts to produce a boosted correlation distribution; and
determining a range shift corresponding to a maximum correlation in the boosted correlation distribution;
adjusting the range profile to compensate for the range shift corresponding to the maximum correlation; and
outputting the adjusted range profile to an inverse synthetic aperture radar to determine a feature of a target.

### Claim 2 (depends on 1)

The computer implemented method according to claim 1, wherein a size of the region of range shifts is based on a shape of the previous correlation distribution.

### Claim 3 (depends on 2)

The computer implemented method according to claim 2, wherein the region of range shifts includes all range shifts with correlation values that are within a predefined threshold of a peak value of the previous correlation distribution.

### Claim 4 (depends on 1)

The computer implemented method according to claim 1, wherein a size of the region of range shifts is based on a range resolution of the range profiles or an expected velocity of a target.

### Claim 5 (depends on 1)

The computer implemented method according to claim 1, wherein adjusting the range profile to compensate for the range shift comprises shifting the range profile by the range shift corresponding to the maximum correlation.

### Claim 6 (depends on 1)

The computer implemented method according to claim 1, wherein selecting the reference range profiles from the plurality of range profiles comprises selecting a plurality of reference range profiles from the plurality of range profiles.

### Claim 7 (depends on 1)

The computer implemented method according to claim 1, wherein the reference range profile is selected from the corresponding set of range profiles.

### Claim 8 (depends on 1)

The computer implemented method according to claim 1, wherein selecting the set of range profiles is based on an expected target velocity.

### Claim 9 (depends on 1)

The computer implemented method according to claim 1, wherein selecting each the set of range profiles is based on a frequency of the corresponding pulses.

### Claim 10 (depends on 1)

The computer implemented method according to claim 1, wherein adjusting each the range profile to compensate for the range shift comprises:
subdividing the range shifts into a plurality of windows;
for each window, fitting a polynomial distribution to the range shifts in the window;
combining the polynomial distributions into a combined distribution;
obtaining a smoothed range shift for each a range profile by sampling from the combined distribution; and
adjusting the range profile to compensate for the smoothed range shift.

### Claim 11 (depends on 10)

The computer implemented method according to claim 10, wherein the method further comprises removing range shifts that exceed a previous or following range shift by a threshold.

### Claim 12 (depends on 10)

The computer implemented method according to claim 10, wherein the plurality of windows partially overlap.

### Claim 13 (depends on 12)

The computer implemented method according to claim according to claim 12, wherein combining the polynomial distributions into a combined distribution comprises taking an average between polynomial distributions within overlapping regions of the plurality of windows.

### Claim 14 (depends on 10)

The computer implemented method according to claim 10, wherein a size of each of the plurality of windows is based on an expected target velocity.

### Claim 15 (depends on 10)

The computer implemented method according to claim 10, wherein a size of each of the plurality of windows is based on a frequency of corresponding pulses.

### Claim 16

A non-transitory machine-readable storage medium storing instructions which, when executed, cause a processing device to perform a method including:
obtaining a plurality of range profiles each representing a plurality of return measurements from a corresponding pulse;
selecting one or more sets of range profiles from the plurality of range profiles;
for a selected set of range profiles, selecting a reference range profile from the plurality of range profiles;
for a selected reference range profile, applying motion compensation to a corresponding set of range profiles based on the reference range profile, wherein applying motion compensation comprises:
for a range profile of the selected set of range profiles in the corresponding set of range profiles, correlating the range profile with the reference range profile to produce a corresponding correlation distribution;
determining for a first correlation distribution of the correlation distributions a range shift corresponding to a maximum correlation in the correlation distribution, the maximum correlation indicating correlation values that are within a predefined threshold of a peak value in the correlation distribution;
for a subsequent correlation distribution from the correlation distributions:
determining a region of range shifts around a determined range shift corresponding to a maximum correlation of a previous correlation distribution;
increasing correlation values for the correlation distribution across the region of range shifts to produce a boosted correlation distribution; and
determining a range shift corresponding to a maximum correlation in the boosted correlation distribution;
adjusting the range profile to compensate for the range shift corresponding to the maximum correlation; and
outputting the adjusted range profile to an inverse synthetic aperture radar to determine a feature of a target.

### Claim 17

A system comprising:
a memory; and
a processing device, operatively coupled with the memory, to:
obtain a plurality of range profiles each representing a plurality of return measurements from a corresponding pulse;
select one or more sets of range profiles from the plurality of range profiles;
for a selected set of range profiles, select a reference range profile from the plurality of range profiles;
for a selected reference range profile, apply motion compensation to a corresponding set of range profiles based on the reference range profile, wherein applying motion compensation comprises:
for a range profile of the selected set of range profiles in the corresponding set of range profiles, correlate the range profile with the reference range profile to produce a corresponding correlation distribution;
determine for a first correlation distribution of the correlation distributions a range shift corresponding to a maximum correlation in the correlation distribution, the maximum correlation indicating correlation values that are within a predefined threshold of a peak value in the correlation distribution;
for a subsequent correlation distribution from the correlation distributions:
determine a region of range shifts around a determined range shift corresponding to a maximum correlation of a previous correlation distribution;
increase correlation values for the correlation distribution across the region of range shifts to produce a boosted correlation distribution; and
determine a range shift corresponding to a maximum correlation in the boosted correlation distribution;
adjust the range profile to compensate for the range shift corresponding to the maximum correlation; and
output the adjusted range profile to an inverse synthetic aperture radar to determine a feature of a target.

### Claim 18 (depends on 1)

The computer implemented method according to claim 1, wherein adjusting the range profile to compensate for the range shift comprises:
subdividing the range shifts into a plurality of windows;
for each window, fitting a polynomial distribution to the range shifts in the window; and
combining the polynomial distributions into a combined distribution, wherein combining the polynomial distributions into a combined distribution comprises taking an average between polynomial distributions within overlapping regions of the plurality of windows.