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,Folie
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
Digital
Beamforming
Current SAR: 1 m v.s. 10 km; 16 m v.s. 100 km
Displaced Phase Center Antenna
>> high spatial resolution
Horb
SCORE algorithm
>> high gain
score (t )  1(t )
R(t)
nadir
Multichannel Antenna
HRWS: 1 m v.s. 70 km (stripmap single-pol)
Wide transmit pattern
>> wide swath
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HRWS Reference System Parameters
Monostatic System
Planar phased array antenna
8,75 m
1,06 m
0,088 m
12 Tile
1,25 m
Total Nr. TRMs
(Transmit-Receive Modules)
...
Panel 1
Panel 2
2 Tile
Elevation: 12 dig. chan.
1 Tile
Azimuth: 7 dig. chan.
Panel 7
...
Orbit Height: 520 km
Antenna Tilt Angle: 34,3 deg
Fully Polarimetric
RF Center Frequency: 9,6 GHz
Pulse Bandwidth: 408 ÷ 194 MHz
Processed Doppler bandwidth: 5950 Hz (stripmap)
SCORE operation
Tx patterns in az. and elev. by Phase Spoiling
Averaged Tx Power: 2171 W
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HRWS Basic Performance
The basic performance of the HRWS has been already investigated
In Stripmap single-pol Mode:
o
6 subswaths cover the complete access range
o
Swath width: 70 - 80 km
o
Spatial resolution: 1 m x 1 m
o
NESZ < - 20.7 dB
o
RASR: < - 28 dB
o
AASR < - 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: 6
Subswath width: 70 - 80 km
Spatial resolution: 1 m x 1 m
Nr. Subswaths: 12
Swath width smaller: 20 - 50 km
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Requirements & Constraints
Severe requirements and constraints characterize the Quad-pol mode
1)
Quad-pol: High PRF

2)

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 @ subswath width (RASR, NESZ)

Low sidelobe level (RASR)
*PRF matched to the antenna length and No. of apertures
> 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

Tx
Phase Spoiling and uniform tapering
(mainlobe  subswath width)
- - - Rx
Hamming window ( side lobe level)
- 19 dB
far range
Hamming vs. Uniform:
improvement in far range - 4 dB
 RASR Cross-pol < - 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 < - 27 dB
 NESZ < - 19,5 dB
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Stripmap Quadpol: Azimuth Performance
Azimuth Resolution
Azimuth Ambiguity Signal Ratio
- 30,5 dB
1,1 m
 Az. Res. < 1,1 m
 AASR < - 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
Mainlobe-width:
azimuth resolution
Mainlobe-level:
NESZ
Ripple:
Scalopping
Side Lobe Level:
AASR
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--Rx Patt.
___
Tx Patt.
___
2-way Patt.
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UW ScanSAR: Azimuth Performance
Azimuth Resolution
8,7 m
Azimuth Ambiguity Signal Ratio
Scalloping
Stripmap: 1 m
Scansar: 7 m gives high scalloping (>3.5dB)
-24 dB
2,1 dB
 Az. Res. < 8,7 m
 AASR < - 24 dB
 Scalloping < 2,1 dB
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UW ScanSAR: NESZ & RASR
Noise Equivalent Sigma Zero
Range Ambiguity Signal Ratio
- 28 dB
- 22,6 dB
 NESZ < - 22,6 dB
 RASR < - 28 dB
ground range resolution: 1 m
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Summary and Conclusions
o
o
Quad-Pol, Stripmap Mode
o
12 subswaths, swath width: 20 - 50 km
o
Spatial resolution: 1 m x 1 m
o
NESZ < - 19.5 dB
o
RASR: Cross-Pol < - 19 dB, Co-Pol < - 27 dB
o
AASR < - 30.5 dB
ScanSAR Mode: Ultra-Width Swath
o
1 swath, swath width 375 km
o
Spatial resolution: 1 m x 9 m
o
NESZ < - 22.6 dB
o
RASR < - 28 dB
o
AASR < - 24 dB
o
Scalloping < 2.1 dB
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