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IGARSS 2011, Vancouver Octavio.Ponce@dlr.de
Octavio Ponce, Pau Prats, Marc Rodriguez-Cassola, Rolf Scheiber, Andreas Reigber
Microwave and Radar Institute (HR)
German Aerospace Center
Processing of Circular SAR TrajectoriesProcessing of Circular SAR Trajectorieswith Fast Factorized Back-Projectionwith Fast Factorized Back-Projection
July 28th, 2011Microwaves and Radar Institute Slide 2
Outline
Circular SAR (CSAR)
Fast Factorized Back Projection (FFBP)
FFBP for Circular SAR
Experimental Results
Conclusions
July 28th, 2011Microwaves and Radar Institute Slide 3
Acquisition Geometry
.
h
x
y
z
R
July 28th, 2011Microwaves and Radar Institute Slide 4
2D Sinc
Resolution – Stripmap 2D IRF
Kx
Kr
r
az
y
xTime Domain Frequency Domain
July 28th, 2011Microwaves and Radar Institute Slide 5
Resolution – CSAR 2D IRFy
xTime Domain
y Kx
Ky
x
Frequency Domain
Soumekh et al, IEEE TIP, 1996
July 28th, 2011Microwaves and Radar Institute Slide 6
Resolution – CSAR 1D IRF
CSAR L-Band
Stripmap L-Band
July 28th, 2011Microwaves and Radar Institute Slide 7
Tomography CSAR
Similar to Computer-aided Tomography 360°
Resolves altitude ambiguities
Shadow “removal”
a
b
Terrain
y x
z
July 28th, 2011Microwaves and Radar Institute Slide 8
Tomography CSAR– Simulated 3D IRF
yx
3D
2D Slice
Surface – 2D Slice
y x
z
Ishimaru, IEEE TGRS, 1998
July 28th, 2011Microwaves and Radar Institute Slide 9
Outline
Circular SAR (CSAR)
Fast Factorized Back Projection (FFBP)
FFBP for Circular SAR
Experimental Setup and Results
Conclusions
July 28th, 2011Microwaves and Radar Institute Slide 10
Challenges of CSAR Processing
Topography accommodation
Real Track
Time efficient algorithm
High accuracy in amplitude and phase
July 28th, 2011Microwaves and Radar Institute Slide 11
Fast Factorized Back Projection (FFBP)
Key points of FFBP (L. Ulander et al., IEEE TAES 2003):
Recursive division of the synthetic aperture (no cost)
After the division, the smallest sub-apertures are back-projected on a polar grid centred on each sub-aperture (~N3/2k)
Recursive addition of the sub-apertures by means of interpolations between polar grids (quality-dependent)
July 28th, 2011Microwaves and Radar Institute Slide 12
Fast Factorized Back Projection (FFBP)
L/8 L/8 L/8 L/8 L/8 L/8
L/4 L/4
L/2
L/4 L/4
L/2
L/8 L/8
L
FOCUSED IMAGE
Lm BP
P2P
P2P
P2P
P2Final Grid
k2 Lmk=1
k=2
k=3
k2 Lm
k2 Lm
k2 Lm k2 Lm
k2 Lm
k2 Lm
Ulander et al, IEEE TAES, 2003
July 28th, 2011Microwaves and Radar Institute Slide 13
Why Polar Coordinates?
kr
krr
rx
kr
kx
Spatial Domain (small sub-aperture) Frequency Domain
Polar to Cartesian
2D FFT
2D FFT
July 28th, 2011Microwaves and Radar Institute Slide 14
x…
y x
z
FFBP for Spotlight/Stripmap – P2P
July 28th, 2011Microwaves and Radar Institute Slide 15
Outline
Circular SAR (CSAR)
Fast Factorized Back Projection (FFBP)
FFBP for Circular SAR
Experimental Setup and Results
Conclusions
July 28th, 2011Microwaves and Radar Institute Slide 16
Modifications of FFBP for CSAR
The orientation of the polar grid for each sub-aperture changes following the circular trajectory.
The polar-to-polar interpolation needs to project first to ground coordinates and then back to the new polar centre.
The DEM must be generated (interpolated) for each polar centre.
July 28th, 2011Microwaves and Radar Institute Slide 17
FFBP for CSAR - Geometry
Top View
x
y
July 28th, 2011Microwaves and Radar Institute Slide 18
FFBP for CSAR - Geometry
Top View
x
y
July 28th, 2011Microwaves and Radar Institute Slide 19
FFBP CSAR - P2P Interpolation
Zoom Top View
to
Ground range
Project
Translate
Rotate
Get and
July 28th, 2011Microwaves and Radar Institute Slide 20
FFBP for CSAR - Geometry
Top View
.
July 28th, 2011Microwaves and Radar Institute Slide 21
Outline
Circular SAR (CSAR)
Fast Factorized Back Projection (FFBP)
FFBP for Circular SAR
Experimental Results
Conclusions
July 28th, 2011Microwaves and Radar Institute Slide 22
FFBP CSAR - Simulation
PRF 400Hz
Band L
BW 94MHz
Radius 4500m
Height 4000m
Terrain 700m
.
July 28th, 2011Microwaves and Radar Institute Slide 23
FFBP CSAR - Simulation
*Interpolator Knab Pulse of 21 points
BP vs FFBP
Knab, IEEE TIT, 1979
July 28th, 2011Microwaves and Radar Institute Slide 24
FFBP CSAR - Performance Speed Up
System, Geometry, Hardware, Interpolator
BP CPU ~238days
25000 x 25000 pixels
Speed up factor
BP GPU ~3 days
FFBP CPU ~11 hrs
FFBP GPU ~3 hrs
July 28th, 2011Microwaves and Radar Institute Slide 25
DLR’s (German Aerospace Center) E-SAR SystemLidar DEM availableKaufbeuren, Germany (2008)Fully Polarimetric: HH-HV-VV Carrier Frequency: 1.3GHz (L-Band)Bandwidth: 94MHzHeight Mean: ~3,200mCircle Radius: ~4,500mRoll Angle: ~10°Depression Angle: ~30°
Experimental Setup
July 28th, 2011Microwaves and Radar Institute Slide 26
Experimental Results - BP vs FFBP
Optical Image CSAR Image
150 x 150 m; Δφ=360°
July 28th, 2011Microwaves and Radar Institute Slide 27
Experimental Results - BP vs FFBP
1.0
0.99
10°
-10°
0°
Coherence Interferogram
Coh. Std. Dev. 0.000599 Phase Std. Dev. 1.7 °
July 28th, 2011Microwaves and Radar Institute Slide 28
Polarimetric Results - Subapertures
Pauli
1240 x 1240 m; Δφ=10°
July 28th, 2011Microwaves and Radar Institute Slide 29
CSAR vs Strimap SAR
1500 x 1500 mE-SAR L-band, 94MHz bandwidth
July 28th, 2011Microwaves and Radar Institute Slide 30
CSAR vs Strimap SAR
E-SAR L-band, 94MHz bandwidth
July 28th, 2011Microwaves and Radar Institute Slide 31
E-SAR L-band, 94MHz bandwidth
CSAR vs Strimap SAR
July 28th, 2011Microwaves and Radar Institute Slide 32
E-SAR L-band, 94MHz bandwidth
CSAR vs Strimap SAR
180 x 180 m
July 28th, 2011Microwaves and Radar Institute Slide 33
E-SAR L-band, 94MHz bandwidth
Circular SAR vs Strimap SAR
180 x 180 m
July 28th, 2011Microwaves and Radar Institute Slide 34
DEM + 0m
Tomography CSAR
DEM + 2m DEM + 3m DEM + 4m
E-SAR L-band, 94MHz bandwidth
July 28th, 2011Microwaves and Radar Institute Slide 35
Luneberg Lens
1500 x 1500 m
July 28th, 2011Microwaves and Radar Institute Slide 36
Tree
E-SAR L-band, 94MHz bandwidth
Tomography CSAR -5m < H < 15m
300 x 300 m
July 28th, 2011Microwaves and Radar Institute Slide 37
FFBP adapted to CSAR successfully:Topography accommodation Real trackHigh improvement in the Speed-up FactorHigh accuracy
Implementation in a graphic processor unit (GPU)
Experimental results with DLR’s E-SAR data have been used to validate the algorithm
Currently processing new “multi-circular” F-SAR campaign
Conclusions
July 28th, 2011Microwaves and Radar Institute Slide 38
Thanks for your attention!
Octavio Ponce: octavio.ponce@dlr.de
Pau Prats: pau.prats@dlr.de
DLR (German Aerospace Center)
HR (Microwaves and Radar Institute)
July 28th, 2011Microwaves and Radar Institute Slide 39
References
H. Oriot, H. Cantalloube, “Circular SAR imagery for urban remote sensing” ,EUSAR 2008.
A. Ishimaru, Chan, Kuga, “An Imaging Technique Using Confocal Circular Synthetic Aperture Radar”, IEEE Transactions on Geoscience and Remote Sensing, Vol. 36, No.5, Septemper 1998.
M. Soumekh, “Synthetic Aperture Radar Signal Processing with Matlab Algorithms”, John Wiley & Sons, Inc.
M. Pinheiro, P. Prats, R. Scheiber, M. Nannini, and A. Reigber, “Tomographic 3D reconstruction from airborne circular SAR,” in Geoscience and Remote Sensing Symposium, 2009 IEEE International, IGARSS 2009, 2009, vol. 3, pp. III–21 – III–24.
Lars M. H. Ulander and et. al., “Synthetic-Aperture Radar Processing Using Fast Factorized Back-Projection,” IEEE Transactions on Aerospace and Electronic Systems, vol. 39, no. 3, pp. 760–776, July 2003.
M. Rodriguez-Cassola, P. Prats, G. Krieger, and A. Moreira, “Efficient Time-Domain Focussing for General Bistatic SAR Configurations: Bistatic Fast Factorised Backprojection,” in European Conference on Synthetic Aperture Radar (EUSAR), Jun 2010.
July 28th, 2011Microwaves and Radar Institute Slide 40
FFBP for CSAR – Computational Load
July 28th, 2011Microwaves and Radar Institute Slide 41
Knab Pulse Band-Limited Interpolation
Knab, IEEE TIT, 1979
July 28th, 2011Microwaves and Radar Institute Slide 42
Hardware
CPU GPU
Processor Intel® Xeon® Tesla® C2070
RAM 24GB 6GB
Cores 8 488
Clock 2.4GHz 1.15GHz
CC 2.0
July 28th, 2011Microwaves and Radar Institute Slide 43
Acquisition Geometry
Integratedreflectivity
= reflectivityfunction
* transmitted radarsignal
July 28th, 2011Microwaves and Radar Institute Slide 44
Experimental Results
IlluminationFlight Track
-60dB
0dB-6000
[m] 0
6000
-6000 0 6000 [m]
July 28th, 2011Microwaves and Radar Institute Slide 45
FFBP for CSAR – 2D Spectrum Polar
0.70° 1.40° 2.81° 5.62° 11.25°
22.5° 45° 90° 180°
kkr
July 28th, 2011Microwaves and Radar Institute Slide 46
FFBP for CSAR – Flow diagram
Cartesian DEM
Polar DEM
Translation
Rotation
Interpolate to regular (r,α)
Stop splitting
Split Data
Range Compressed Data Final cartesian grid
Compute polar grids (r,α,DEM)
Perform DBP
FFBP CSAR Recursive Kernel
FFBP CSARRecursive Kernel
P2P Interp
Compute polar grids (r,α,DEM)
Interpolate Subimage final grid
P2C Interp
Interpolate Subimages
A
A
Focused Image
No Yes
No No
YesYes