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Performance Investigation on the High-Resolution
Wide-Swath SAR System Operating in Stripmap
Quad-Pol and Ultra-Wide ScanSAR Mode
F. Bordoni, M. Younis, G. Krieger
DLR - Institut für Hochfrequenztechnik und
Radarsysteme
IGARSS 2011, 24-29 July, Vancouver, Canada
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Outline

• Introduction
• HRWS (High-Resolution Wide-Swath) SAR (Synthetic
  Aperture Radar) System
• Reference Parameters
• Stripmap, Quad-Pol (Quadrature Polarimetric) Mode
• Timing Constraints
• Proposed Solution
• Performance
• NESZ (Noise Equivalent Sigma Zero)
• RASR (Range Ambiguity to Signal Ratio)
• AASR (Azimuth Ambiguity to Signal Ratio)
• ScanSAR Mode Ultra-Width Swath
• Timing Constraints
• Proposed Solution
• Performance (NESZ, RASR, AASR, Scalloping)

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HRWS (High-Resolution Wide-Swath) SAR System
The HRWS SAR system is conceived to overcome the
conventional trade-off between resolution and
swath width
Current SAR 1 m v.s. 10 km 16 m v.s. 100
km HRWS 1 m v.s. 70 km (stripmap single-pol)
Multichannel Antenna
Horb
SCORE algorithm gtgt high gain
Displaced Phase Center Antenna gtgt high spatial
resolution
R(t)
nadir
Wide transmit pattern gtgt wide swath
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HRWS Reference System Parameters

• Monostatic System
• Planar phased array antenna

8,75 m
Total Nr. TRMs (Transmit-Receive
Modules) Elevation 12 dig. chan. Azimuth 7
dig. chan.
0,088 m
12 Tile
1,25 m
...
1,06 m
2 Tile
1 Tile
Panel 1
Panel 2
Panel 7
...
Orbit Height 520 km Antenna Tilt Angle 34,3
deg RF Center Frequency 9,6 GHz Pulse
Bandwidth 408 194 MHz Processed Doppler
bandwidth 5950 Hz (stripmap) Averaged Tx Power
2171 W
Fully Polarimetric SCORE operation Tx patterns
in az. and elev. by Phase Spoiling
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HRWS Basic Performance
The basic performance of the HRWS has been
already investigated In Stripmap single-pol
Mode

• 6 subswaths cover the complete access range
• Swath width 70 - 80 km
• Spatial resolution 1 m x 1 m
• NESZ lt - 20.7 dB
• RASR lt - 28 dB
• AASR lt - 26 dB

How performs the HRWS in Quad-Pol, ScanSAR Modes?
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Stripmap Quad-Pol Timing Diagram
Transmit alternately vertical horizontal linear
polarized pulses ? Double PRF (Pulse Repetition
Frequency)
Timing Diagram
Single-pol
Quad-pol
PRF 1650 1780 Hz
PRF double 3400 3800 Hz
Spatial resolution 1 m x 1 m Nr. Subswaths
12 Swath width smaller 20 - 50 km
Spatial resolution 1 m x 1 m Nr. Subswaths
6 Subswath width 70 - 80 km
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Requirements Constraints
Severe requirements and constraints characterize
the Quad-pol mode

• Quad-pol High PRF
• RASR (critical especially in Cross-Pol)

• Multichannel Less degrees of freedom in the PRF
  choice (PRF uniformity)
• AASR (particularly low)
• NESZ (multichannel processing)
• Flexibility Design Elevation Patterns
• Mailobe _at_ subswath width (RASR, NESZ)
• Low sidelobe level (RASR)

PRF matched to the antenna length and No. of
apertures gt regular sampling in azimuth results
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Pattern Design RASR in Cross-Pol
Elev. pattern design crucial to meet the RASR
requirements in Cross-Pol
near range
NESZ
RASR
- 19 dB
far range
Hamming vs. Uniform improvement in far range - 4
dB

• RASR Cross-pol lt - 19 dB

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Stripmap Quadpol RASR in Co-Pol NESZ
Range Ambiguity Signal Ratio Co-Pol Noise
Equivalent Sigma Zero
- 19,5 dB
-27 dB
(spatial resolution 1 m x 1m)

• RASR Co-Pol lt - 27 dB
• NESZ lt - 19,5 dB

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Stripmap Quadpol Azimuth Performance
Azimuth Resolution Azimuth Ambiguity Signal Ratio

• Az. Res. lt 1,1 m
• AASR lt - 30,5 dB

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Ultra-Wide ScanSAR
Imaging of the complete acces range (375 km) in a
single pass
Swath width of 375 km ? complete imaging of the
Earth with a repeat time of 8 days
375 km
Swath width 375 km Spatial resolution 1m x ?m
6 bursts // 6 subswaths
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Pattern Design Performance
Azimuth pattern shape key influence on ScanSAR
performance The Phase Spoiling technique is
used to obtain the Tx pattern
- - - Rx Patt. ___ Tx Patt. ___
2-way Patt.
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UW ScanSAR Azimuth Performance
Azimuth Resolution Azimuth Ambiguity Signal
Ratio Scalloping
8,7 m
Stripmap 1 m Scansar 7 m gives high scalloping
(gt3.5dB)
-24 dB
2,1 dB

• Az. Res. lt 8,7 m
• AASR lt - 24 dB
• Scalloping lt 2,1 dB

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UW ScanSAR NESZ RASR
Noise Equivalent Sigma Zero Range Ambiguity
Signal Ratio

• NESZ lt - 22,6 dB
• RASR lt - 28 dB

ground range resolution 1 m
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Summary and Conclusions

• Quad-Pol, Stripmap Mode
• 12 subswaths, swath width 20 - 50 km
• Spatial resolution 1 m x 1 m
• NESZ lt - 19.5 dB
• RASR Cross-Pol lt - 19 dB, Co-Pol lt - 27 dB
• AASR lt - 30.5 dB
• ScanSAR Mode Ultra-Width Swath
• 1 swath, swath width 375 km
• Spatial resolution 1 m x 9 m
• NESZ lt - 22.6 dB
• RASR lt - 28 dB
• AASR lt - 24 dB
• Scalloping lt 2.1 dB