SAR image formation

Patent metadata

Field	Value
Publication number	US-9329264-B2
Application number	US-201313768046-A
Country	US
Kind code	B2
Filing date	Feb 15, 2013
Priority date	Feb 15, 2013
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

SAR imaging method that includes applying PRF decimation to range-compressed IQ data to generate PRF-decimated range-compressed IQ data for each image block of an image and applying motion compensation to the PRF-decimated range-compressed IQ data to generate motion-compensated data for each image block. The method includes computing first stage image values at image grid point intersections of iso-range lines and vertical grid lines for each image bock based on the motion-compensated data for each image block. The method also includes computing second stage image values for the image grid point intersections by interpolation using the first stage image values at the image grid point intersections and correcting image phase of the second stage image values for the image grid point intersections to generate phase-corrected image values for each image block. The method includes generating a full-resolution SAR image by summing the phase-corrected image values for each image block.

First claim

The invention claimed is:

1. A synthetic aperture radar (SAR) imaging method for processing moving air borne radar acquired images for multiple performance matrices, the method comprising:
physically acquiring SAR in-plane and quadratic data from a scan of an image grid
applying range pulse compression to SAR in-phase and quadrature (IQ) data for each image block of a SAR image grid to generate range-compressed IQ data for each image block;
applying pulse range frequency (PRF) decimation to the range-compressed IQ data to generate PRF-decimated range-compressed IQ data for each image block;
applying motion compensation to the PRF-decimated range-compressed IQ data to generate motion-compensated data for each image block;
computing first stage image values at image grid point intersections of iso-range lines and vertical grid lines for each image block based on the motion-compensated data for each image block;
computing second stage image values for the image grid point intersections by interpolation using the first stage image values at the image grid point intersections;
correcting image phase of the second stage image values for the image grid point intersections to generate phase-corrected image values for each image block; and
generating a full-resolution SAR image by summing the phase-corrected image values for each image block.

2. The method of claim 1 , wherein the step of applying motion compensation comprises performing a fast Fourier transform in the SAR image grid range dimension.

3. The method of claim 2 , wherein the fast Fourier transform in the SAR image grid range dimension is performed in accordance with:

S
′

⁡

(

n
,
i

)

=

∑

k
=
0

Nfft
-
1

⁢

S
⁡

(

k
,
i

)

·

ⅇ

-
j2π

·
n

⁢

⁢

k
Nfft

⁢

⁢
for
⁢

⁢
i

∈

[

1
,
2
,
3
,
…
⁢

,

N
p

]

where S(k,i) is a two-dimensional range compressed SAR response with k being range bin index and i being pulse index, N p is number of pulses in a processing pulse group, and Nfft is the least integer power of 2 greater than the number of slant range bins covering the processed image block.

4. The method of claim 3 , comprising calculating
S 1 ( n,i )= S′ ( n,i )·Ref( n )

by multiplying S′(n,i) with a reference function of the form:
Ref( n )==exp(− i 2π· n 1·Δ R ( i )/Δ r s ),

where n=[1,2,3 . . . , Nfft], n1=[0,1,2 . . . , Nfft/2−1,−Nfft/2,−Nfft/2+1, . . . , −1], ΔR(i)=R(i)−R(i c ), where R(i) is distance between a reference scatter and the SAR at pulse i which is within a range of [1,2,3, . . . , N p ], and i c =N p /2+1.

5. The method of claim 4 , wherein the motion-compensated data for each image block is determined by performing a fast Fourier transform in the range dimension in accordance with:

S
mocomp

⁡

(

k
,
i

)

=

∑

n
=
0

Nfft
-
1

⁢

S
1

⁡

(

n
,
i

)

·

ⅇ

-
j2π

·
k

⁢

⁢

n
Nfft

⁢

⁢
for
⁢

⁢
i

∈

[

1
,
2
,
3

Assignees

• Raytheon Co

Inventors

• Jin Michael Y

Classifications

• G01S13/9035 Primary

  Physics · mapped topic

• G01S2007/2883

  Physics · mapped topic

• G01S13/90

  using synthetic aperture techniques {, e.g. synthetic aperture radar [SAR] techniques} · CPC title

• G01S2007/2886

  Physics · mapped topic

• G01S13/5242 Primary

  with means for platform motion or scan motion compensation, e.g. airborne MTI · CPC title