Adaptive SAR Results with the LiMIT Testbed

Transcription

1 Adaptive SAR Results with the LiMIT Testbed Gerald Benitz Adaptive Sensor Array Processing Workshop 7 June

2 Outline LiMIT collection platform SAR sidelobe recovery Electronic Protection (EP) Summary

3 LiMIT X-Band SAR Capability Lincoln Multi-mission ISR Testbed (LiMIT) Resolution Spot size (10 km alt, 25 km range) 2004 Capability 1.0 m (180 MHz, 2s)* 1.5 km 4 km *Bandwidth and integration time AESA Receivers and A/D 3.5 TB RAID IMU

4 LiMIT AESA Antenna Active Electronically Scanned Array (AESA) Beam Steering Computer (BSC) Phased Array Controller (PAC) Operating Band Inst Bandwidth Antenna Area Scan Range GHz) LMIT AESA X-Band, 4 GHz BW 1 sq ft # Channels 8 subarrays, 2 Aux (H/V) Beams Agility > 600 MHz ± 66 az,± 66 el # TR Modules 384 Avg Transmit Power (@20% Duty) DC Power (20% duty) 200 W 3.5kW Multiple simultaneous beams (up to 4) Antenna Mass (density) ~60kg (600 kg/m 2 ) 19 Subarray Details T/R module at every Element (0.6 in x 0.6 in)

5 Data Collection Campaigns Pease International Tradeport, (NH) Ft. Huachuca, (AZ) N E V A D A Las Vegas Nellis AFB Lowry Lane Test Track 3.5 km ft Runway Radar Checkout Instrumented Civilian Vehicles SAR / GMTI 15 C A L I F O R N I A M E X I C O 10 Phoenix 8 Ft. Huachuca 17 A R I Z O N A Tucson 19 Instrumented Military Vehicles Electronic Attack SAR / GMTI JUL AUG SEP OCT Pease International Tradeport, (NH) Navy Silent Hammer (SCI, CA) Checkout Automated Data Processing Instrumented Civilian Vehicles / Ships SAR / SMTI Military Experiment On-board Processing Off-board Dissemination Instrumented Military Vehicles / Ships SAR / SMTI

6 Outline LiMIT collection platform SAR sidelobe recovery Electronic Protection (EP) Summary

7 Aerial Photograph of Pease ITP with SAR Image Overlayed Pease International Tradeport Image Parameters 1 m x 1 m resolution 3.75 km x 2.55 km swath Display: 28 db dynamic range July 8, 2004 Maiden flight

8 AESA-Enabled Sidelobe Recovery LiMIT collection, July 8, 2004 (Pease International Tradeport) BW = 3.7 deg PRF = 2000 Hz Subarray Beam Transmit Beam Transmit sidelobes illuminate Doppler-ambiguous clutter that is visible to the subarrays -13 db PRF/2 0 PRF/2

9 AESA-Enabled Sidelobe Recovery LiMIT collection, July 8, 2004 (Pease International Tradeport) BW = 3.7 deg PRF = 2000 Hz Side Lobe Main Lobe Receive Beam Main Lobe Main Lobe Side Lobe -3BW -2BW 2BW 3BW -3/2PRF PRF -PRF/2 0 PRF/2 PRF 3/2PRF

10 Adaptive Sidelobe Recovery Algorithm Comparison AESA Conventional SAR 2 KHz-wide image X 2-D FFT Spotlight steering applied Tapered steering vector Adaptive Sidelobe Recovery Similar to post-doppler STAP Weight vector re-use reduces computation AESA Spotlight steering applied 8 Registered Images 8-Channel 2-D FFT Training w/ noise loading Range-Doppler cell Beamformer w = R -1 v w X 6 KHz-wide ambiguity-free image Steering vector for main lobe and sidelobes

11 Outline LiMIT collection platform SAR sidelobe recovery Electronic Protection (EP) Summary

12 Ft. Huachuca, AZ, EP Collection 24 July m/s 5 squint Blinking Mainlobe Jammer DSB-modulated noise w/carrier 32 db JNR 0.69 beamwidths off aim N Aim Point Jammer 1.3 km 26 km 8.7 km N W Magnitude (db) JammerSpectrum 9.72 GHz Carrier MHz Bandwidth Frequency (GHz) A/D Counts Jammer On Jammer 17 Hz Off Time History Full Scale: 128 Counts Clutter + Noise Pulse Number

13 EP Result: Single-Pulse DBU Blinking Mainlobe Jammer Non-Adaptive SAR Jammer 0.7 BW Target LiMIT Collection 24 July 2004 Ft. Huachuca 32 db JNR Image Parameters Beam deshading causes brightening 1 m x 1 m resolution 3.75 km x 2.4 km swath 28 db dynamic range 0.75 m pixels Jammer Carrier

14 EP Result: Single-Pulse DBU Blinking Mainlobe Jammer Non-Adaptive SAR Adaptive Beamformed SAR LiMIT Collection 24 July 2004 Ft. Huachuca 32 db JNR Image Parameters 1 m x 1 m resolution 3.75 km x 2.4 km swath 28 db dynamic range 0.75 m pixels Jammer Line-of-Sight

15 EP Result: Single-Pulse DBU Blinking Mainlobe Jammer Non-Adaptive SAR Adaptive Beamformed SAR LiMIT Collection Reflectors 2.5 Ton Truck Reflectors 2.5 Ton Truck 24 July 2004 Ft. Huachuca 32 db JNR Image Parameters 1 m x 1 m resolution 3.75 km x 2.4 km swath 28 db dynamic range 0.75 m pixels *EP = Electronic Protection Jammer Line-of-Sight

16 Single-Pulse DBU Algorithm Comparison AESA Conventional SAR 2 KHz-wide image X 2-D FFT Spotlight steering applied Tapered steering vector Polar format focus Single-Pulse DBU AESA Frequency domain pulse data x f Frequency-varying beamformer X 2-D FFT 2 KHz-wide image w f DBU: train over frequency w f = w0 + f w&, frequency-varying weights Novel beam constraint with noise loading Polar format focus

17 Motivating Post-Doppler EP Goal: Track Jammer Over CPI Beamwidths Jammer Line of Bearing Time (s) Avoid Beam Modulation Jammer Off Jammer On Pre-Doppler Jammer Relative Phase Change Domains Post-Doppler Jammer Relative Shift AESA Channel 1 Mid-AESA CPI 11 Image Doppler Transform Correlated Samples Image Doppler Axis Concept: Use Doppler-tap filters to restore jammer coherence

18 Range & Doppler Tap Filters Algorithm Comparison Old Adaptive Sidelobe Recovery Similar to post-doppler STAP Weight vector re-use reduces computation 8 registered images Range-Doppler cell AESA Spotlight steering applied 8-channel 2-D FFT Beamformer w = R -1 v w X 6 KHz-wide ambiguity-free image Training w/ noise loading Steering Vector for main lobe and sidelobes Polar format focus

19 Range & Doppler Tap Filters Algorithm Comparison New Range & Doppler Tap Filters Similar to adjacent-bin post-doppler STAP AESA (pairwise presum) Spotlight steering applied Tap Delays 2-D FFT, Apply tap delays of 0.1 bin Beamformer w = R -1 v Doppler Cell 16 registered images Range Cell Training Samples Range-Doppler cell w X Σ Steering Vector(s) for the Doppler bin, including sidelobes 3 KHz-wide jammer & ambiguity-free image Polar format focus

20 EP Result: Range & Doppler Tap Filter Blinking Mainlobe Jammer LiMIT July 24, 2004 collection at Ft. Huachuca 3070 Hz recovered from 2 KHz PRF Conventional Spotlight SAR (Doppler unwrapped and de-shaded for comparison) Image Parameters 1 m x 1 m resolution 1.3 km x 6.4 km swath 25 db dynamic range 32 db JNR 1535 Hz Doppler -1.9 Beamwidth Jammer Carrier 16 DOF Adaptive SAR 1535 Hz Doppler 1.9 Beamwidth Jammer Location (-0.69 beamwidths)

21 EP Result: Range & Doppler Tap Filter Blinking Mainlobe Jammer LiMIT July 24, 2004 collection at Ft. Huachuca Reflectors 3070 Hz recovered from 2 KHz PRF 2.5 Ton Conventional Spotlight SAR (Doppler unwrapped and de-shaded for comparison) Truck Image Parameters 1 m x 1 m resolution 1.3 km x 6.4 km swath 25 db dynamic range 32 db JNR 1535 Hz Doppler -1.9 Beamwidth Jammer Carrier Reflectors 16 DOF Adaptive SAR 1535 Hz Doppler 1.9 Beamwidth 2.5 Ton Truck Jammer Location (-0.69 beamwidths)

22 Summary The LiMIT testbed provides high quality AESA data TBytes collected over urban, desert and littoral areas AESA enables recovery of Doppler-ambiguous clutter Demonstrated 6 khz recovery using 2 khz PRF AESA enables main-lobe jammer cancellation (EP) Demonstrated 1 m SAR image recovery at 32 db JNR, along with recovery of Doppler-ambiguous clutter Algorithms are designed to preserve SAR quality Pulse-domain DBU over frequency using a novel gain constraint and noise loading preserves range-profile fidelity Image-domain tap-delay filters preserve both range- and Doppler-profile fidelity, and recovers Doppler ambiguities

23 EP Performance Metrics Range & Doppler Tap Approach 30 SINR before and after EP (simulated) 40 JNR before and after EP (simulated) db db Doppler Frequency (Hz) Noise gain Doppler Frequency (Hz) db Doppler Frequency (Hz)

24 Effect of Reduced Degrees of Freedom Range & Doppler Tap Approach Images show residual difference versus the 16 DOF result Using 12 DOF (combining DOFs below) shows negligible residual vs. 16 DOF No Delay Taps (4 DOF) Image Parameters Doppler Tap Only (8 DOF) 1 m x 1 m resolution 1.3 km x 6.4 km swath 3 db dynamic range Range Tap Only (8 DOF) Transmit Null Jammer Location Jammer Carrier