1、20 Dec 2005,Bistatic 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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,2,Agenda,Bistatic SAR Bistatic Im
2、age Reconstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,3,Bistatic SAR,In a Bistatic configuration, the Transmitter and Receiver are spatially separated and can m
3、ove 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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,4,Current Research,Several Eur
4、opean 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 interferom
5、etry 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.,20 Dec 2005,Bistatic SAR Imag
6、ing 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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,6,Image Reconstruction Issues,Bistatic
7、 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
8、same range of closest approach do not necessarily collapse into the same trajectory in the azimuth frequency domain.,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,7,Image Reconstruction Issues,Bistatic SAR has many configurations parallel tracks, non-parallel tracks, stationary rec
9、eiver etc. These different configurations make the derivation of the spectrum difficult Analytical solution is not available, however approximate solution exist Loffelds bistatic equation Restricted the scope of research to focusing parallel and slightly non-parallel cases,20 Dec 2005,Bistatic SAR I
10、maging using Non-Linear Chirp Scaling,8,Imaging geometry of bistatic SAR,20 Dec 2005,Bistatic 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,
11、20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,10,Existing Algorithms,Time Domain Correlation Back Projection Algorithm K Algorithm Loffelds Bistatic Equations RDA Roccas Smile,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,11,Agenda,Bistatic SAR Bistatic Image Reco
12、nstruction Issues Existing Algorithms Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions,20 Dec 2005,Bistatic 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 Ap
13、plications of Nonlinear Chirp Scaling in SAR Data Processing,“ in IEEE Trans. Geosci. Remote Sensing, May 2001. 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 ext
14、ended to other geometries parallel tracks, non-parallel tracks,20 Dec 2005,Bistatic 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 configuration NLCS requires no interpolation NLCS can be used
15、in non-parallel cases 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.,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,14,Main Processing Steps of NLCS Algorithm,Range
16、Compression,Linear RCMC,Non-Linear Chirp Scaling,Azimuth Compression,Baseband Signal,Focused Image,20 Dec 2005,Bistatic 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 Po
17、int B has the same Closest range of approach and the same chirp rate.,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,16,Chirp Rate Equalization (monostatic),20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,17,After LRCMC, trajectories at the same range gate do not hav
18、e 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 hpert() along azimuth time . Monostatic CaseBistatic Case with Stationary
19、Receiver,20 Dec 2005,Bistatic 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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling
20、,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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Sca
21、ling,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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,21,Residual QRCMC,Uncorrected QRCM will lead to Broadening in Ra
22、nge 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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,22,Perturbation Function,We have extended the NLCS algorithm to
23、 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 syste
24、m,20 Dec 2005,Bistatic 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 re
25、version of power series,20 Dec 2005,Bistatic 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 Ph
26、ase,20 Dec 2005,Bistatic 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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Sca
27、ling,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 Algor
28、ithm suitable for shorter wavelengths (S, C , X, K band ) and cases where QRCM is not too significant,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,27,Invariance Region Analysis,Bistatic case, Tx imaging at 30 deg squint, Tx slant range of 40km, lateral separation of 20km and squin
29、t of 30 deg.,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.,20 Dec 2005,Bistatic SAR Imaging using Non-Lin
30、ear 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 efficien
31、cy 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,20 Dec 2005,Bistatic SAR
32、Imaging using Non-Linear Chirp Scaling,29,Illustration of SRC,20 Dec 2005,Bistatic 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,20 Dec 200
33、5,Bistatic 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
34、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,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,32,Before Registration to Ground Plane,20 Dec 2005,Bistatic SAR Ima
35、ging using Non-Linear Chirp Scaling,33,After Registration to Ground Plane,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,34,Impulse response,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,35,Agenda,Bistatic SAR Bistatic Image Reconstruction Issues Existing Algorithm
36、s Non-Linear Chirp Scaling Algorithm Extension to NLCS Simulation Results Conclusions,20 Dec 2005,Bistatic 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 no
37、n-parallel track example and the results,20 Dec 2005,Bistatic 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.,20 Dec 2005,Bistatic SAR Imaging using Non-Linear Chirp Scaling,38,Questions?,
