US 6,603,424 B1 · System, method and computer program product for reducing errors in synthetic aperture radar signals

Abstract

A system is provided for reducing errors in synthetic aperture radar signals from a plurality of range lines where each range line includes a plurality of azimuth positions. The system comprises an autofocus processor for receiving a plurality of slow-time samples. The autofocus processor can estimate a phase error for each slow-time sample by a maximum likelihood technique and thereafter compensate the plurality of slow-time samples by the estimated phase errors to obtain a plurality of range-line samples. The implementation of the maximum likelihood technique is done by a superresolution technique along slow-time samples which also estimates a plurality of Doppler frequencies and amplitudes for a plurality of point scatterers at each range line. Further, the autofocus processor can also predict the performance of the autofocus technique by computing a resulting root mean square error of the estimated phase error which is derived form the corresponding Cramer Rao bound.

Claims39

Dependent claims

A method of reducing errors in synthetic aperture radar signals from a plurality of range lines where each range line includes a plurality of azimuth positions, said method comprising:

receiving a plurality of slow-time samples representing radar signals for a plurality of azimuth positions for a plurality of range lines;
estimating a phase error for each slow-time sample;
compensating the plurality of slow-time samples by the estimated phase errors to obtain a plurality of range-line samples;
processing the range-line samples according to a superresolution signal processing technique to thereby obtain a plurality of Doppler frequencies for a plurality of point scatterers at each range line;
reconstructing a true signal for each range line based upon the plurality of Doppler frequencies;
and
obtaining a correction to the estimated phase error for each slow-time sample based upon the range-line samples and the true signals.

4 more elements

A method of determining an accuracy of estimated phase errors in synthetic aperture radar signals, wherein the signals are from a plurality of range lines that each includes a plurality of azimuth positions, said method comprising:

calculating true signals for a plurality of slow-time samples for the plurality of range lines, wherein the plurality of slow-time samples represent radar signals for a plurality of azimuth positions for a plurality of range lines;
determining a true signal power for each slow-time sample summed over the plurality of range lines and a total true signal power, wherein the true signal powers are based upon the true signals and the total true signal power is based upon amplitudes of the scatterers;
determining a Cramer Rao Bound (CRB) based upon a clutter-plus-receiver noise power, the true signal powers, a dominate scatterer power, the number of slow time samples and the total true signal power;
and
determining a root mean square error based upon the CRB.

2 more elements

A system for reducing errors in synthetic aperture radar signals from a plurality of range lines where each range line includes a plurality of azimuth positions, said system comprising:

an autofocus processor capable of receiving a plurality of slow-time samples representing radar signals for a plurality of azimuth positions for a plurality of range lines, wherein said autofocus processor is also capable of estimating a phase error for each slow-time sample and thereafter compensating the plurality of slow-time samples by the estimated phase errors to obtain a plurality of range-line samples, wherein said autofocus processor is further capable of processing the range-line samples according to a superresolution signal processing technique to thereby obtain a plurality of Doppler frequencies for a plurality of point scatterers at each range line, wherein said autofocus processor is further capable of reconstructing a true signal for each range line based upon the plurality of Doppler frequencies and thereafter obtaining a correction to the estimated phase error for each slow-time sample based upon the range-line samples and the true signals.

A system for determining an accuracy of estimated phase errors in synthetic aperture radar signals, wherein the signals are from a plurality of range lines that each includes a plurality of azimuth positions, said system comprising:

a processing element capable of calculating true signals for a plurality of slow-time samples for the plurality of range lines, wherein the plurality of slow-time samples represent radar signals for a plurality of azimuth positions for a plurality of range lines, wherein said processing element is also capable of determining a true signal power for each slow-time sample summed over the plurality of range lines and a total true signal power, wherein the true signal powers are based upon the true signals and the total true signal power is based upon amplitudes of the scatterers, said processing element additionally being capable of determining a Cramer Rao Bound (CRB) based upon a clutter-plus-receiver noise power, the true signal powers, a dominant scatterer power, the number of slow time samples and the total true signal power, and wherein said processing element is further capable of determining a root mean square error based upon the CRB.

A computer program product for reducing errors in synthetic aperture radar signals from a plurality of range lines where each range line includes a plurality of azimuth positions, said computer program product comprising a computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program portions comprising:

a first executable portion for receiving a plurality of slow-time samples representing radar signals for a plurality of azimuth positions for a plurality of range lines;
a second executable portion for estimating a phase error for each slow-time sample;
a third executable portion for compensating the plurality of slow-time samples by the estimated phase errors to obtain a plurality of range-line samples;
a fourth executable portion for processing the range-line samples according to a superresolution signal processing technique to thereby obtain a plurality of Doppler frequencies for a plurality of point scattersers at each range line;
a fifth executable portion for reconstructing a true signal for each range line based upon the plurality of Doppler frequencies;
and
a sixth executable portion for obtaining a correction to the estimated phase error for each slow-time sample based upon the range-line samples and the true signals.

4 more elements

A computer program product for determining an accuracy of estimated phase errors in synthetic aperture radar signals, wherein the signals are from a plurality of range lines that each includes a plurality of azimuth positions, said computer program product comprising a computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program portions comprising:

a first executable portion for calculating true signals for a plurality of slow-time samples for the plurality of range lines, wherein the plurality of slow-time samples represent radar signals for a plurality of azimuth positions for a plurality of range lines;
a second executable portion for determining a true signal power for each slow-time sample summed over the plurality of range lines and a total true signal power, wherein the true signal powers are based upon the true signals and the total true signal power is based upon amplitudes of the scatterers;
a third executable portion for determining a Cramer Rao Bound (CRB) based upon a clutter-plus-receiver noise power, the true signal powers, a dominant scatterer power, the number of slow time samples and the total true signal power;
and
a fourth executable portion for determining a root mean square error based upon the CRB.

2 more elements

Dependencies are inferred from the claim text.

System, method and computer program product for reducing errors in synthetic aperture radar signals

Life of this patent

System, method and computer program product for reducing errors in synthetic aperture radar signals

Life of this patent

Abstract

Claims39