1. A KU-BAND GEOSYNCHRONOUS SYNTHETIC APERTURE RADAR MISSION ANALYSIS WITH MEDIUM TRANSMITTED POWER AND MEDIUM-SIZED ANTENNA
Josep Ruiz Rodon, Antoni Broquetas, Andrea Monti Guarnieri, Fabio Rocca
07/27/2011
IGARSS’11 Vancouver

2. Outline Introduction to GEOSAR
System description: synthetic aperture formation.
GEOSAR constraints and system features.
Image reconstruction for simulated GEOSAR raw data.
The APS correction for long term acquisitions.
Conclusions.
07/27/2011
IGARSS’11 Vancouver

3. Introduction to GEOSAR (I)
What?: Ku-Band monostatic SAR mission to get high resolution images from a radar system placed in a geosynchronous satellite.
How?: relative motion achieved by the slight perturbations (eccentricity and/or inclination) of the non-perfect geostationary orbit → Synthetic Aperture formation.
Why?: constant monitoring of a wide Earth’s area (revisit time limited only by the synthetic aperture integration time). North-South illumination.
07/27/2011
IGARSS’11 Vancouver

4. Introduction to GEOSAR (II)
Drawbacks: low power echo → increase integration time and/or the resolution cell (degrade resolution). Possible Atmospheric Phase Screen artefacts and target coherence loss due to long integration time.
Configurations:
Monostatic: transceiver on a communications satellite or dedicated geosynchronous satellite.
Bistatic: illuminator of opportunity + receiver tuned to one of the downlink channels or receiver on ground station.
07/27/2011
IGARSS’11 Vancouver

5. System description (I): Synthetic Aperture Formation
Satellite motion with respect to the Earth’s surface governed by eccentricity and inclination of the orbit.
Longitude and latitude histories with respect to an Earth’s centered rotating reference system:
Typically, elliptical tracks are obtained by tuning the orbital parameters.
(1)
(2)
07/27/2011
IGARSS’11 Vancouver

6. System description (II): Obit design parameters
Orbit design flexibility:
07/27/2011
IGARSS’11 Vancouver

7. GEOSAR constraints and system features (I): timing and PRF selection
PRF selection: avoid transmission interferences and nadir eclipses.
Dartboard diagram PRF=30Hz
Dartboard diagram PRF=100Hz
07/27/2011
IGARSS’11 Vancouver

8. GEOSAR constraints and system features (II): SNR requirements
SNR after SAR processing (pulse compression and integration):
(3)
@12GHz
Compressed
07/27/2011
IGARSS’11 Vancouver

9. GEOSAR constraints and system features (III): APS retrieval
Meteorological applications of GEOSAR: Atmospheric Phase Screen (APS) monitoring. Fast temporal evolution (~minuntes) but high spatial correlation (~Km).
@12GHz
Compressed
07/27/2011
IGARSS’11 Vancouver

10. GEOSAR image reconstruction (I): Doppler behavior
Non-perfect circular orbit → variable Doppler centroid during the acquisition.
Doppler centroid track/compensation from the information of a reference position.
07/27/2011
IGARSS’11 Vancouver

11. GEOSAR image reconstruction (II): Doppler behavior
Example: e= and inc.: 0.046º
Scene: 1 x 1 Km.
Reference target: central scene point.
07/27/2011
IGARSS’11 Vancouver

12. GEOSAR image reconstruction (III): TDBP focusing
Raw data simulation: 1 x 1 Km scene with centered point target during 1 hour.
No atmospheric artifacts and noise considered.
Perfect reconstruction via TDBP algorithm: 50 x 50 meters resolution.
07/27/2011
IGARSS’11 Vancouver

13. APS correction for long term acquisitions (I)
Short term GBSAR acquisitions for long integration time synthetic aperture assessment.
07/27/2011
IGARSS’11 Vancouver

14. APS correction for long term acquisitions (II)
APS correction from phase information of a stable point target (corner reflector).
07/27/2011
IGARSS’11 Vancouver

15. Conclusions
Monostatic GEOSAR configuration with typical LEOSAR parameters with long integration.
Synthetic Aperture formation, timing analysis and SNR requirements shows the feasibility of geosynchronous satellites for SAR applications.
TDBP algorithm to focus simulated raw data from a GEOSAR configuration with Doppler centroid compensation.
Atmospheric phase stability in long term acquisition as well as target coherence loss have to be deeply studied in further analysis.
07/27/2011
IGARSS’11 Vancouver

16. Thank you Josep Ruiz Rodon e-mail: josep.ruiz@tsc.upc.edu
Phone:
07/27/2011
IGARSS’11 Vancouver