Victor C. Chen & Baokun Liu

ANCORTEK INC. USAwww.ancortek.com

HYBRID SAR/ISARFOR DISTRIBUTED ISAR IMAGING

OF MOVING TARGETS

I. Concept of Hybrid SAR/ISARII. Arbitrarily Distributed ISARs with Same

Grazing AnglesIII. Arbitrarily Distributed ISARs with Different

Grazing AnglesIV. Spotlight SAR with Curved Aperture Path V. 3-D Feature Extraction Using Curved Aperture

PathVI. Conclusion and Discussion

OUTLINE

R.J.A. Tough and K.D. Ward, A Theory for Hybrid SAR/ISAR Radar Imaging, Memorandum no. 4532, Defense Research Agency, Malvern, U.K. 1991

“… a theory of hybrid SAR/ISAR imaging …… to identify ways in which these hybrid images

may be processed optimally.”

HYBRID SAR/ISAR CONFIGURATIONS:

1. The Use of ISAR Processing to Focus Moving Target in SAR

2. The Use of SAR processing to Enhance Image Resolution or to Extract 3-D Target Feature in ISAR

I. THE CONCEPT OF HYBRID SAR/ISAR

Ship 2

Ship 1

APPLY ISAR PROCESSING TO FOCUS MOVING TARGET IN SAR

X-band Stripmap SAR3-15 m resolution

M. Martorella, F. Berizzi, E. Giusti, and A. Bacci, " Refocusing of moving targets in SAR images based on inversion mapping and ISAR processing," IEEE 2011 Radar Conference, 2011.

ISAR ISAR ISARISAR

ISARISAR ISARISAR

ISAR

Moving target

APPLY SAR PROCESSING TO ENHANCE RESOLUTION IN ISAR

D. Pastina, M. Bucciarelli and P Lombardo, "Multistatic and MIMO distributed ISAR for enhanced cross-range resolution of rotating targets", IEEE Trans. on Geoscience and Remote Sensing, vol. 48, no. 8, pp. 3300-3317, 2010.

LINEARLY FLYING IN FORMATION

Tx/RxTx/Rx Tx/RxTx/RxTx/Rx

ARBITRARILY DISTRIBUTED GROUND-BASED ISARs FOR IMAGING OF MOVING TARGETS

ARBITRARILY DISTRIBUTED GROUND-BASED ISARs

MOVING TARGET

A NUMBER OF NEARBY RADARS DISTRIBUTED WITHIN A LIMITED AREA ALONG COAST, SHORE OR MOUNTAIN

II. ARBITRARILY DISTRIBUTED ISARS WITH SAME GRAZING ANGLES

ISAR no.1

ISAR no.2ISAR no.N

Elevation

AzimuthSame grazing angles

All ISARs are time synchronized and collect data during the same time frame

FROM ARBITRARILY DISTRIBUTION TO CIRCULAR ARC DISTRIBUTION

ISAR no.1

ISAR no.2

ISAR no.N

Elevation

Azimuth

Arbitrarily distributed

Circular distributed

RE-ARRANGE ISAR VIEW ANGLES TO FORM A LARGE SAR VIEW ANGLE

ISAR no.1

ISAR no.2

ISAR no.N

Elevation

Azimuth

Circular distributed

T T T T

ISAR-1 ISAR-2 ISAR-3 ISAR-4 ISAR-5

Integration Time

View Angle

T1 T2 T 3 T 4 T 5

T1 T2

T

T4

NTTN

nn

1

TNTN

nn

1

Overlapped

ξ1 ξ2 ξ4 ξ5ξ 3

T3 T5

t1 t2 t3 t4 t5

0

5

10

15

-4

-2

0

2

4

0

0.2

0.4

0.6

0.8

1

YX

Z

ISAR no.5 ISAR no.4

ISAR no.3ISAR no.2

ISAR no.1

Target

GEOMETRY OF ARBITRARILY DISTRIBUTED ISARs AND TARGET CENTER

SIMULATION STUDY

-1.5 -1 -0.5 0 0.5 1 1.5-1

0

1

-0.1

-0.05

0.05

0.1

0.15

0.2

0.25

0.3

X

Target Model

Y

Z

0

SAME HEIGHTS

-1.5 -1 -0.5 0 0.5 1 1.5-1

0

1

-0.1

-0.05

0.05

0.1

0.15

0.2

0.25

0.3

X

Target Model

Y

Z

0

-15 -10 -5 0 5 10 15-60

-50

-40

-30

-20

-10

0

Doppler (Hz)

Inte

nsity

(dB

)

Doppler Resolution

Combined ISARs

ISAR no.3

Ra

ng

e (m

ete

r)

Doppler (Hz)

(b) Combined full aperture range-Doppler image

-3 -2 -1 0 1 2 3-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Ra

ng

e (m

ete

r)

Doppler (Hz)

(a) Range-Doppler image of ISAR no.3

-3 -2 -1 0 1 2 3-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Enhanced resolution in cross-range domain

3-D TARGET LAYOVER PHENOMENA IN 2-D ISAR IMAGERY

Cro

ss-R

ang

e

Image Projection Plane

Slant-Range

3-D Target Model

2-D ISAR Image

Layoverphenomena

III. ARBITRARILY DISTRIBUTED ISARS WITH DIFFERENT GRAZING ANGLES

ISAR no.1

ISAR no.2

ISAR no.N

1

2

N

Elevation

Azimuth

A NUMBER OF NEARBY ISARS DISTRIBUTED WITHIN A LIMITED AREA ALONG COAST, SHORE OR MOUNTAIN.

SAR WITHCURVED APERTURE PATH

Different grazing angles

Ra

ng

e (m

ete

r)

Doppler (Hz)

Range-Doppler Image of combined ISARs with different grazing angles

-3 -2 -1 0 1 2 3-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Ra

ng

e (m

ete

r)

Doppler (Hz)

Range-Doppler image of combined ISARs with same grazing angles

-3 -2 -1 0 1 2 3-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

(a) (b)

2-D image becomesBlurred and geometric

distorted

Spotlight SARaperture path

i = 1,2,3,…

Elevation

Azimuth

targetρ(x,y,z)

ξi

i

x

y

z

uihielevation

angle

azimuthangle

i

PROJECTION SLICE THEOREM

IV. SPOTLIGHT SAR WITH CURVED APERTURE PATHDistributed ISARs with different grazing angles is similar to

a SAR with curved aperture path

ξ

X

Y

Z

0

u

vw

Observation direction

ξ

kx

0

kuky

kz

pξ(u)

Projection(observed

radar return)

g(x,y,z)

Target RCS density

3-D observation space 3-D Fourier space

Pξ(ku)

Fourier transformof the projection

dwdvwvuzwvuywvuxgup )],,(),,,(),,,([)( duedvdwzyxg

dueupkP

ujk

ujku

u

u

),,(

)()(

SAR

DATA FREQUENCY SPACE

2-D SAR ImageElevation

Azimuth

3-D Target

APERTURE PATH

SPOTLIGHT SAR WITH LINEAR APERTURE PATH

AT THE SAME HEIGHT

2-DDATA SURFACE

PROJECTION SLICE

THEOREM

Elevation

Azimuth

2-D SARImage Plane

2-D APERTURE ARRAY

3-DDATA CUBE

V. 3-D FEATURE EXTRACTION USING CURVED APERTURE PATH

SAR DATA FREQUENCY SPACE

3-D SAR ImageElevation

Azimuth

3-D Target

APERTURE PATH

Elevation

Azimuth

3-D SARImage Cube

PROJECTION SLICE THEOREM

elevation

azimuth

SPOTLIGHT SAR WITH CURVED APERTURE

PATH

3-DDATA SURFACE

Spotlight SAR

DATA FREQUENCY SPACE

3-D Data in Frequency SpaceElevation

Azimuth

3-D Target

CURVED APERTURE PATH

elevation

azimuth

Elevation

Azimuth

3D SAR Data Surface

RE-ARRANGE ISAR APERTURE ELEVATIONS TO FORM A 2-D APERTURE ARRAY

Spotlight SAR

DATA FREQUENCY SPACE

3-D Data in Frequency SpaceElevation

Azimuth

3-D Target

CURVED APERTURE PATH

Elevation

Azimuth

3D SAR Data Surface

elevation

azimuthelevation

total elevationcoverage

view angle of an ISAR

total elevationcoverage

view angle of an ISAR

From CURVED APERTURE PATH to 2-D APERUTRE ARRAY

From 3-D SAR DATA SURFACE to 3-D SAR DATA CUBE

3-D ISARdata cube

-1.5 -1 -0.5 0 0.5 1 1.5-1

0

1

-0.1

-0.05

0.05

0.1

0.15

0.2

0.25

0.3

X

Target Model

Y

Z

0

TARGET MODEL

3-D SAR IMAGERY OF THE TARGETFROM A CURVED APERTURE PATH

60

80

30 40 50 60 70 80 90

65

70

75

80

85

90

95

100

Y

X

Zz

Y

X

3-D Tomographic Imaging3-D Filtered-Backprojection Algorithm

Same cross-range resolutionBut gain 3-D information

Curved Aperture Path

Ground Truth

3-D SAR imagery

Field Trial Data reported by Naval Surface Warfare Center, Carderock Division.

X-band Radar was carried on a helicopter. Data was captured with a curved aperture

path. Ground target at 300 m distance. The target consists of 13 corner reflectors

on the ground plane and 7 corner reflectors mounted on a tripod.

* Ken Knaell, Three-dimensional SAR from curvilinear aperture, 1996 IEEE Radar Conference, pp. 2230-2238.

7 corner reflectors

13 corner reflectors

18 corner reflectorsare reconstructed.2 corner reflectors are missing due to shadowing.

3-D Projection Slice Theorem 3-D Backprojection Algorithm

tripod

• If ISAR platforms are at different heights, the combined SAR data is equivalent to the data generated by SAR with curved aperture path.

• Different grazing view angles make 2-D image blurring and geometric distortion.

• In the case of ground-based ISARs with different grazing view angles, we should take the advantage of the curved aperture path to capture 3-D feature of the target.

VI. CONCLUSION AND DISCUSSION