Study of Polarimetric Calibration for Circularly Polarized Synthetic Aperture Radar

Transcription

1 Study of Polarimetric Calibration for Circularly Polarized Synthetic Aperture Radar CEOS WORKSHOP 2016 Yuta Izumi, Sevket Demirci, Mohd Zafri Baharuddin, and Josaphat Tetuko Sri Sumantyo JOSAPHAT MICROWAVE REMOTE SENSING LABORATORY CENTER FOR ENVIRONMENTAL REMOTE SENSING, JAPAN 1

2 Contents 1 Background 2 Polarimetric calibration method 3 Calibration experiment and result 4 Discussion and Future work 2

3 L Band CP-SAR onboard JX-1 Chirp Pulse Generator JX-1 RF-System Hyperspectral camera Josaphat Tetuko Sri Sumantyo, Chapter 12. Circularly Polarized Synthetic Aperture Radar onboard Unmanned Aerial Vehicle (CP-SAR UAV), Kenzo Nonami et al. edn., Autonomous Control Systems and Vehicles, Springer, December 2012.

4 X Band CP-SAR System for Aircraft Antenna RX0 Antenna RX1 Antenna 9.4G RF Unit (RX) Work Station TX0 TX1 Antenna SSD MEM DAC ADC Oscillator 9.4G RF Unit (TX)

5 Principle of Circularly Polarized Synthetic Aperture Radar (CP-SAR) L-RHCP Top +Z L-LHCP L-RHCP Forward +X Bottom -Z (EP-SAR & CP-SAR : Patent Pending : )

6 Rice paddy observation Background Category Specification Frequency [GHz] 4.5 to 7.5 Polarization CP and LP Number of samples 801 Number of azimuth point 359 Off-nadir angle [deg] 70 and 50 7

7 Background Rice paddy observation Off nadir angle: 70deg 6 rice paddy LL LR RL RR 8

8 Background Full polarimetric calibration for Circularly polarized Radar system Concept Well developed conventional calibration Objective technique in linear polarization (LP) basis is used for calibration of circular polarization (CP) radar system. We utilize the two conventional calibration technique and modified it for CP full polarimetric calibration. The performance of the two calibration techniques in CP basis are validated by experiment inside an anechoic chamber. 9

9 Polarimetric calibration method The LP polarimetric calibration techniques used for CP polarimetric calibration LP calibration technique CP calibration technique Wiesbeck et al. technique Gau et al. technique 10

10 Polarimetric calibration method The typical relationship between measured and theoretical scattering matrix Receive system Rx Target Transmit system Tx theoretical scattering matrix m m S S ILL ILR RLL RLR SLL SLR TLL TLR m m IRL I S S RR RRL R RR SRL S RR TRL T RR LL LR RL RR Measured scattering matrix Isolation matrix Distortion matrix 11

11 Polarimetric calibration method Wiesbeck et al. technique modified for CP calibration technique This technique solves the complete polarimetric error model, where every error coefficients of the distortion matrices can be solved by three calibration targets. m m S S ILL ILR RLL RLR SLL SLR TLL TLR m m IRL I S S RR RRL R RR SRL S RR TRL T RR LL LR RL RR 1. Wiesbeck, W., et al. Single reference, three target calibration and error correction for monostatic, polarimetric free space measurements, in Proceedings of the IEEE, vol. 79, no. 10, , Oct

12 Polarimetric calibration method Calibration targets LP calibration Cal 1 Cal 2 Cal 3 CP calibration Cal 1 Cal 2 Cal 3 Sphere/ circular disk Dihedral Dihedral 45 Calibration process Start Dihedral Dihedral 45 Sphere/ circular disk Calculate [S] of Circular plate, Dihedral, and Dihedral45 Measure [I] Measure Cal1 Measure Cal2 Measure Cal3 Derive error coeficients End 13

13 Polarimetric calibration method Gau et al. technique modified for CP calibration technique This technique separate the channel effect and cross-talk coefficients in the model. Two calibration targets are utilized. Channel effect: Axy Cross-talk coefficients: dx, dy M LL ALL M 1 LL ALR d y SLL SLR 1 d x M A M A d 1 S S d 1 LL RL LL RR x RL RR y 1. Gau, J. R., et al. New polarimetric calibration technique using a single calibration dihedral, in IEE Proceedings - Microwaves, Antennas and Propagation, vol. 142, no. 1, 19-25, Feb

14 Polarimetric calibration method Calibration targets LP calibration CP calibration Cal 1 Cal 2 Cal 1 Cal 2 Dihedral Dihedral 45 Calibration process Start Sphere/ circular disk Dihedral Calculate [S] of Circular plate, Dihedral Measure [I] Measure Cal1 Measure Cal2 Derive dx, dy and Axy End 15

15 Polarimetric calibration method Modified parts Calculating theoretical scattering matrix in CP-basis Use of basis transformation matrix. SLL SLR 1 1 j SHH SHV 1 j S S 2 j 1 S S j 1 RL RR VV VV Calibration targets Combination of the calibration targets are different. 16

16 PC Vector network analyzer (VNA) Calibration experiment and results Experimental setup Frequency: 4.5~7.5 GHz Number of samples for each frequency: 801 Anechoic chamber(6.6 4m) Phase shifter Rx antenna Range distance 4.7m Target Tx antenna 17

17 Calibration experiment and results Calibration targets Circular plate (Single scattering) Dihedral (Double scattering) Dihedral (45 ) (Double scattering) SLL SLR 0 j SRL S RR j 0 SLL SLR 1 0 SRL S RR 0 1 j90 SLL SLR e 0 -j90 RL RR S S 0 e CT1: Wiesbeck et al. technique modified for CP. Targets CT 1 CT2 Cal target 1 Vertical dihedral Vertical dihedral CT2: Gau et al. technique modified for CP. Cal target 2 Dihedral 45 None Cal target 3 Circular plate Circular plate 18

18 Calibration experiment and results Calibration reflectors Circular plate 200mm (Diameter) (Large circular plate) 150mm (Small circular plate) Dihedral 180x180x400mm (Large dihedral) 150x150x200mm (Small dihedral) 19

19 Calibration experiment and results Measured target Cal1, Cal2 Cal3 Large circular plate Small dihedral Small circular plate 2 M LL 10 2 M LR 10log SLL SLR 0 j SRL S RR j 0 2 M LR 10 2 M RL 10log M M LR RL 20

20 Calibration experiment and results Measured target Cal1, Cal2 Cal3 Small dihedral 45 Large dihedral Large circular plate j90 SLL SLR e 0 -j90 RL RR S S 0 e 10log 2 M LR 10 2 M LL 2 M LL 10 2 M RR 10log M M LL RR 21

21 Conclusion Conclusion and Future work For basic study of CP GB-SAR system, we assessed the performance of the CP full polarimetric calibration techniques. Two calibration techniques are validated by experiment. Future work The CP calibration technique for UAV, aircraft, and satellite will be investigated for next laboratory s experiment. 22

22 Study of Polarimetric Calibration for Circularly Polarized Synthetic Aperture Radar Thank you for your attention 23

23 Benefit of CP-SAR Circular polarizations (CP) performs better than the HH polarization at lower incidence angles [1-2]. CP exhibits multiple benefits over linear polarization including CP avoids polarization losses due to misalignment CP is no need to keep the transmitting and receiving antenna in the same alignment; It has the ability to decrease interference between direct and reflected signal due to multipath propagation The CP has the advantage of compactness and low power requirement, since the transmission of CP microwave is not affected by the Faraday rotation effect in the ionosphere [3] etc References [1] S. Angelliaume, P. Martineau, P. Durand, and T. Cussac, Ship Detection and Sea Clutter Characterisation Using X&L-Band Full- Polarimetric Airborne SAR Data, Proceedings of SeaSAR Norway, 2012, pp [2] R. Touzi, On the use of polarimetric SAR data for ship detection, Proceedings of Geoscience and Remote Sensing Symposium, vol. 2, 1999, pp [3] J. T. Sri-Sumantyo, Development of Circularly Polarized Synthetic Aperture Radar (CP-SAR) Onboard Small Satellite, PIERS Proceedings, Marrakesh, Morocco, 2011, pp

24 Specification CB-SAR: Altitude (h): < 4,000 m Frequency operation (f): 5.3 GHz Single polarization: LP / CP Pulse length (t): ms Pulse bandwidth (B): MHz Off nadir angle (g m ): degrees Platform (UAV) speed (v): m/s Signal to Noise ratio (SNR): 20 db Antenna length (l): 0.75 m Antenna width (w): 0.2 m Antenna efficiency : 80% Noise temperature (T): 500 K Noise Figure (F): 3 db Pulse repetition frequency (PRF): 1000 Hz Swath width (Wg): < 600 m Best azimuth resolution: 0.67 m Best range ground resolution: 0.67 m Duty cycle (Dc): 1.1% - 1.6% Peak transmit power (Pt): < 400 Watts Backscattering coefficient (s ): -30 db TX Attenuator 0 db to -20 db (1 db stepped setting by computer) RX Attenuator -20 db (fixed switch) 25

25 X Band SAR : Specification Items Center Frequency Spec 9.4GHz Frequency Bandwidth 800MHz Transmit Power 1500W peak X Band Antenna Slant Range Resolution Azimuth Resolution Flight Altitude 1m 5m ~5,000m Spectrum analyzer Local Unit 19inch size AWG CP-SAR Antenna : Tilted 30 degrees for downward Oscilloscope TX Unit RX Unit X Band CP-SAR System [Instruments] 26

26 Specification of Microsatellite SAR Altitude Microsatellite SAR Polar Orbit, 500~900 km Mission Devices Mission Period Payload Power Altitude Control Data rate Telecommunication Memory Size Circular Polarized SAR (CP-SAR) Electron Density Temperature Probe (EDTP) 1-3 Year 100kg 150 kg Average < 600W 3 axis, accuracy 0.1 CSS,IRU,STT,MAGS,GPSR,RWA,MTQ 120Mbps S Band(TLM/CMD) X Band (Mission Data, 20 Mbps) 10 GBytes About 700ⅹ800ⅹ1850 mm(launch) Top +Z Forward +X Bottom -Z

27 Boeing CP-SAR Antenna : Tilted 30 degrees for downward Radome

28 Polarimetric calibration method The technique modified from Wiesbeck et al. m S I RR RR M R T R T R T R T S m S I LL M R T R T R T R T S m S I M R T R T R T R T S RL RL M R T R T R T R T S S LR RR RR RR RL LR RR LR RL RR RR LL LL LR RL LL LL LR LL LL RL LL LL RL RR RL RL LL RR LL RL RL RL m LR LR RR LL LR LR LR LL RR LR ILR SRR S SRL S LR Calibration requirement Three calibration targets should be utilized. Linearly independent each other Error matrix S S S S RR LL RL LR 29

29 Polarimetric calibration method The technique modified from Gau et al. Channel effect: Axy Cross-talk coefficients: dx, dy M LL ALL M 1 LL ALR d y SLL SLR 1 d x M A M A d 1 S S d 1 LL RL LL RR x RL RR y Calibration requirement Two calibration targets should be utilized Linearly independent 30