T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 1 Bistatic SAR imaging using Non-Linear Chirp Scaling By Y. L. Neo Supervisor : Prof. Ian Cumming Industrial Collaborator : Dr. Frank Wong

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 2 Agenda Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 3 Bistatic SAR In a Bistatic configuration, the Transmitter and Receiver are spatially separated and can move along different paths. Bistatic SAR is important as it provides many advantages –Cost savings by sharing active components –Improved observation geometries –Passive surveillance and improved survivability

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 4 Current Research Several European radar research institutes - DLR, ONERA, QinetiQ and FGAN have embarked on bistatic airborne experiments. Majority of the experiments uses two existing monostatic sensors to synthesize bistatic images. Satellite missions are also proposed TanDEM – X : proposal for TerraSAR-X single pass interferometry for accurate DEM DTED-3. Interferometric Cartwheel. Excellent paper – Multistatic SAR Satellite Formations: Gerhard Krieger. Other research involves the use of Bistatic Parasitic SAR. Where a ground based receiver pairs up with a non-cooperative satellite transmitter.

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 5 Agenda Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 6 Image Reconstruction Issues Bistatic SAR data, unlike monostatic SAR data, is inherently azimuth-variant. Difficult to derive the spectrum of bistatic signal due to the double square roots term. Traditional monostatic SAR algorithms based on frequency domain methods are not able to focus bistatic SAR imagery, since targets having the same range of closest approach do not necessarily collapse into the same trajectory in the azimuth frequency domain.

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 7 Image Reconstruction Issues Bistatic SAR has many configurations –parallel tracks, –non-parallel tracks, –stationary receiver etc. These different configurations make the derivation of the spectrum difficult –Analytical solution is not available, however approximate solution exist – Loffeld’s bistatic equation –Restricted the scope of research to focusing parallel and slightly non-parallel cases

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 8 Imaging geometry of bistatic SAR

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 9 Agenda Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 10 Existing Algorithms Time Domain Correlation Back Projection Algorithm  K Algorithm Loffeld’s Bistatic Equations –RDA –Rocca’s Smile

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 11 Agenda Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 12 Non-Linear Chirp Scaling Existing Non-Linear Chirp Scaling –Based on paper by F. H. Wong, and T. S. Yeo, “New Applications of Nonlinear Chirp Scaling in SAR Data Processing," in IEEE Trans. Geosci. Remote Sensing, May –Assumes negligible QRCM (for SAR with short wavelength) –shown to work on Monostatic case and the Bistatic case where receiver is stationary –Limitations of this method is unknown –May be extended to other geometries – parallel tracks, non-parallel tracks

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 13 Advantages NLCS can be used to focused bistatic data by finding the perturbation function for each bistatic configurationNLCS can be used to focused bistatic data by finding the perturbation function for each bistatic configuration NLCS requires no interpolationNLCS requires no interpolation NLCS can be used in non-parallel casesNLCS can be used in non-parallel cases The Linear RCMC step in NLCS eliminates most of the RCM and the range/azimuth phase coupling.The Linear RCMC step in NLCS eliminates most of the RCM and the range/azimuth phase coupling. Computational load is comparable to traditional monostatic algorithms.Computational load is comparable to traditional monostatic algorithms.

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 14 Main Processing Steps of NLCS Algorithm Range Compression Linear RCMC Non-Linear Chirp Scaling Azimuth Compression Baseband Signal Focused Image

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 15 Monostatic Case Az time Range time A B C –The trajectories of three point targets in a squinted monostatic case is shown –Point A and Point B has the same Closest range of approach and the same chirp rate. –After Range Compression and LRCMC, Point A and Point C now lie in the same range gate. Although they have different chirp rates

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 16 Chirp Rate Equalization (monostatic)

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 17 After LRCMC, trajectories at the same range gate do not have the same chirp rates, an equalizing step is necessary Once the Azimuth Chirp Rate is equalized, the image can be focused by an azimuth matched filter. Chirp rates are equalized by phase multiply with a perturbation function h pert (η) along azimuth time. –Monostatic Case Bistatic Case with Stationary Receiver

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 18 Agenda Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 19 Research work done Added residual QRCMC Extended the processing to parallel tracks and non-parallel tracks Azimuth Frequency Matched filter Secondary Range Compression Current work –Invariance Region Analysis –Registration to ground plane

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 20 We have added a QRCMC to improve the impulse response Residual QRCM Correction can be performed in the range Doppler domain after the Chirp Rate has been equalized Range Compression LRCMC / Linear Phase Correction Azimuth Compression Baseband Signal Focused Image Non-Linear Chirp Scaling Residual QRCMC

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 21 Residual QRCMC Uncorrected QRCM will lead to Broadening in Range and Azimuth The Cubic RCM is very small compared to Quadratic RCM, can be ignored in most cases Without residual QRCMC With residual QRCMC Resolution and PSLR Improves

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 22 Perturbation Function We have extended the NLCS algorithm to Non-Parallel Tracks with the Same Velocity Using the method similar to the monostatic case and correction of the phase term up to the cubic term, the perturbation function is found to be a cubic function of azimuth time and the coefficient is found to be Limited to short and medium wavelength system

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 23 Azimuth Frequency Matched Filter Initially used time domain matched filter – correlation (inefficient) Frequency matched filter is derived using the reversion of power series Linear phase term has to be removed before applying the reversion of power series

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 24 Azimuth Matched Filter Freq matched filter can be obtained by doing a FT of the equalized Az signal A relation between azimuth time and azimuth frequency can be obtained by using the Principle of Stationary Phase

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 25 Azimuth Matched Filter The Frequency matched filter is the conjugate of FT signal Expansion up to third order phase is necessary - e.g. C band 55deg squint 2m resolution

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 26 Limitations Restriction on patch size, residual RCM difference < 1 range resolution cell – restrict the range extent The Non-linear chirp scaling uses some approximations – leading to restriction in azimuth extent Range Doppler Coupling for large QRCM – Secondary Range Compression is necessary Algorithm suitable for shorter wavelengths (S, C, X, K band ) and cases where QRCM is not too significant

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 27 Invariance Region Analysis Wavelength (Frequency) Resolution0.01m (30GHz)0.03m (10GHz)0.06m (5GHz)0.2m (1.5GHz) 10 mFull size 3 mFull size 3.4 km 1 mFull size4.5km2.1km0.6km Bistatic case, Tx imaging at 30 deg squint, Tx slant range of 40km, lateral separation of 20km and squint of 30 deg. Bistatic case, Tx imaging at 30 deg squint, Tx slant range of 40km, lateral separation of 20km and squint of 30 deg. Wavelength (Frequency) Resolution0.01m (30GHz)0.03m (10GHz)0.06m (5GHz)0.2m (1.5GHz) 10 mFull size 3 mFull size 4.0 km 1 mFull size2.7km1.3km0.4km The range invariance region to keep range and azimuth resolution degradation less than 10% for a 10 km by 10km patch. Bistatic case, imaging at broadside with Tx slant range of 40km, lateral separation of 20km and a bistatic angle of 9 deg. Bistatic case, imaging at broadside with Tx slant range of 40km, lateral separation of 20km and a bistatic angle of 9 deg.

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 28 Secondary Range Compression Range Doppler Coupling occurs for large QRCM i.e. longer wavelength and higher resolution cases Secondary Range Compression must be performed before Quadratic Range Cell Migration for these cases Additional processing required will reduce the efficiency of the algorithm Still investigating this part. Preliminary results shows that quadratic range migration of 6 range resolution cells does not produce significant range Doppler coupling Diagram referenced from “the BOOK” – Digital Processing of Synthetic Aperture Radar Data

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 29 Illustration of SRC

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 30 Agenda Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 31 Non-parallel flight, dissimilar velocity Transmitter squinted at 40 degrees and both platforms moving in a non-parallel configuration with lateral separation of 3km and with Vt = 200m/s and Vr =220m/s1 parallel to Transmitter. It is a C- band system with wavelength = 0.06m, 3dB beamwidth = 1.9degree, PRF = 185Hz. Range bandwidth of 75MHz and Azimuth bandwidth about 160Hz. The imaged area has 25 point targets

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 32 Before Registration to Ground Plane

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 33 After Registration to Ground Plane

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 34 Impulse response

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 35 Agenda Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 36 Conclusions Illustrated the use of NLCS to focus bistatic SAR Show the extensions to the NLCS to improve its processing capabilities Simulated a non-parallel track example and the results

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 37 Future work Invariance Region Analysis. Secondary Range Compression. Registration. Comparison with existing algorithms. How the existing algorithms relate to one another.

T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A 20 Dec 2005Bistatic SAR Imaging using Non-Linear Chirp Scaling 38 Questions?