EARLY DEVELOPMENT IN SYNTHETIC APERTURE LIDAR SENSING FOR ON-DEMAND HIGH RESOLUTION IMAGING

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2 EARLY DEVELOPMENT IN SYNTHETIC APERTURE LIDAR SENSING FOR ON-DEMAND HIGH RESOLUTION IMAGING ICSO 2012 Ajaccio, Corse, France, October 11th, 2012 Alain Bergeron, Simon Turbide, Marc Terroux, Bernd Harnisch*, Linda Marchese INO 2740 rue Einstein Québec, QC G1P 4S4 Canada ESA, ESTEC - TEC-MMO2200 AG Noordwijk, Keplerlaan 1, The Netherlands alain.bergeron@ino.ca

3 Outline Overview of Synthetic Aperture Radar SAR Optronic Processor Introduction to Synthetic Aperture Lidar All Optronic SAL System Summary 3

4 SYNTHETIC APERTURE RADAR OVERVIEW A SAR system can take images of the earth s surface, through clouds and dense atmosphere, day or night, in adverse conditions x (Azimuth) y (Ground range) By translating the aperture, SAR overcomes the diffraction limit of the system Synthetized aperture much larger than the physical aperture in the azimuth direction 4

5 SAR DATA A synthetized large antenna generates large amounts of complex-valued raw data SAR Raw Data Block These large data sets are not easily transferred from satellite to ground (difficult to compress) The processing (raw data to image) is time-consuming.

6 SAR: data processing An optical SAR processor has been developped at INO (Performed under an ESA contract) The optical SAR processor generates in real-time SAR images from SAR raw data. SAR images are easier to compress and transmit to the ground SAR images can be compressed SAR raw data can be compressed 50X 4X Compact lightweight SAR optical processor prototype High Definition active components: 1920 x 1080 pixels Real-time processing of Envisat ASAR raw data 6

7 Optronic SAR Processor Mass: SAR and Relay = 6.1 kg Power consumption: 17 W Extern Dimensions: L x H x W = 621 mm x 207mm x 140 mm 7

8 On-Demand Image Reconstruction Image Section Raw Data Amplitude Camera SLM #1 Complex Raw Data Raw Data Phase Laser SLM #2 The amplitude raw data pattern is superimposed onto the phase raw data pattern The complex raw data are propagated through the optronic processor where the lenses refocus the raw data to form an image The final image is captured on the CMOS camera 8

9 Taormina & Santa Margherita, Sicily Google Maps Visible Image Optronically Processed Envisat/ASAR Image 9

10 Synthetic Aperture Lidar (SAL) SAL is the extension of SAR to much shorter wavelengths (1.5 μm vs 5 cm) SAL can achieve higher resolution than SAR with small size aperture: images are more easily interpreted Could potentially provide centimeter-class resolution for observation range of thousand kilometers (resolution depends on real aperture) Active sensor: day/night operation Generate large data sets: the high resolution of SAL generates even higher data throughput than a SAR. The optronic processor would still allow real-time image processing 10

11 Applications of SAL SAL could act as a complementary tool for SAR: large area coverage with SAR zoom over an area of interest with SAL Urban surveillance Civilian security monitoring (ex: monitoring of area during flood period) Small platform: short deployment time 11

12 Synthetic Aperture Lidar Laboratory demonstration λ sweep from nm Pulse duration = 0.32 s (~ µs for SAR) Pulse bandwidth=4thz (~ MHz for SAR) Distance lens-target : up to 3 m Laser power = 22 mw Eye safe 12

13 SAL Acquistion Set-Up Target on a translation stage Target Lens Beam collimator Beam size vs target Detector 13

14 Optronic Processing The INO optronic processor has been designed to reconstruct SAR images from ENVISAT/ASAR data Parameters of ENVISAT/ASAR and SAL prototype are different SAL data must thus be reformatted to match the SAR data format prior to sending it into the SAR processor 14

15 SAL Reconstructed Image: target #1 : range = 1.26 m 14 mm Digital processing 4.5 mm Target made of white paper Raw results, no focusing technique applied Optronic processing 15

16 SAL Reconstructed Image: target #2 : range = 3 m Optronic processing Target made of white paper Image following retroreflective tape removal from 14-bit data and contrast enhancement Focusing performed digitally (based on the retroreflector signals) with PGA 16

17 SAL Resolution Based on feature evaluation: Ground-range resolution: r SAL ~ 80 μm Azimuth resolution: x SAL ~ 280 μm Roughly equivalent to theoretical values The resolution of a real aperture system operating at the same wavelength with the same lens diameter would be, at a range of 3 m, about 440 μm A SAL system would maintain the same resolution with increasing distance 17

18 Summary Early development showed the feasibility of synthetic aperture lidar and optronic SAL processing SAL demonstration with diffusive non-metallic targets Achieved a resolution of about 280 m in azimuth and 80 m in ground range SAL system could allow for timely high-resolution imaging Next step: optronical focus, using the wavefront compensation technique (already implemented in the SAR processor) 18

19 MERCI!

20 Digital Processing SAR FFT along range direction Range match filter IFFT along range direction FFT along azimuth direction Azimuth match filter IFFT along azimuth direction SAL FFT along range direction FFT along azimuth direction Azimuth match filter IFFT along azimuth direction Phase gradient autofocus 20