1 Nonlinear Range Cell Migration (RCM) Compensation Method for Spaceborne/Airborne Forward-Looking Bistatic SAR Nonlinear Range Cell Migration (RCM) Compensation Method for Spaceborne/Airborne Forward-Looking Bistatic SAR Zhe Liu, Jianyu Yang, Xiaoling Zhang School of Electronic Engineering, University of Electronic Science and Technology of China, Chengdu, , China Presentation by Zhe Liu

2 Outline Introduction to the SA-FBSAR and its nonlinear RMC Nonlinear RCM compensation method Simulation results Conclusions and further work

3 Introduction － What is SA-FBSAR Spaceborne/Airborne Forward- Looking Bistatic SAR (SA-FBSAR) Platforms: Transmitter and receiver of SA-FBSAR are low earth orbit (LEO) satellite and aircraft, respectively. Working Modes: Transmitter antenna works in side-looking or squint-looking mode; receiver antenna in forward- looking mode. Target imaging scene: Target scene is along the receiver’s forward-looking direction transmitter receiver Imaging scene

4 Introduction － Emergence of SA-FBSAR MonostaticSAR Bistatic/Multistatic SAR(B/M SAR) SAR(B/M SAR) Spaceborne B/M SAR Airborne S-A B/M SAR Commu.satellite Broadcastsatellite Radarsatellite Diversity of target information High immunity to attacks Low cost Wide coverage, high SNR Platform flexibility Power saving wide band repeated observation SA-BSAR with radar satellite SA-FBSAR attractive potential for aircraft landing and navigation

5 Introduction － Emergence of SA-FBSAR In Nov. 2009, FGAN (German Aerospace Center) launched the first experiment to test the feasibility of SA-FBSAR. Fig.1 Imaging result of the first SA-FBSAR feasibility experiment in 2009

6 Introduction － Challenges of SA-FBSAR imaging · Dramatic geometric difference · Dramatic geometric difference Satellite height ： km Aircraft height ： 1 - 5km · Essential velocity difference · Essential velocity difference Satellite velocity ： km/s Aircraft velocity ： 100m/s · Different working mode · Different working mode Satellite : side-looking Aircraft : forward-looking

7 Introduction － Challenges of SA-FBSAR imaging · Dramatic geometric difference · Dramatic geometric difference · Essential velocity difference · Essential velocity difference · Different working mode · Different working mode Range cell migration (RCM) features are :  Vary with the target’s range and azimuth location  exhibits significant nonlinearity with target’s range location Severe distortion and nonlinear misregistration will occur, if such RCM is not properly compensated

8 Introduction － effect of nonlinear RCM on imaging results Fig2. Imaging result of point targets (a) original point scatterers (b) without RCM compensation

9 x y (a) original area target (b) Without RCMC Introduction － effect of nonlinear RCM on imaging results Fig3. Imaging result of area targets

10 Introduction － Our work  Purpose: find a nonlinear two-dimensional RCM compensation method for SA-FBSAR in frequency domain  Main idea: 1. Set up SA-FBSAR response spectrum model 2. Deduce nonlinear RCM analytic formula 3. Propose SA-FBSAR nonlinear RCM compensation method

11 Nonlinear RCM Compensation for SA-FBSAR － system geometric model Fig.4 SA-FBSAR system geometry

12. Origin of nonlinear RCM

13 Nonlinear RCM Compensation for SA-FBSAR － system signal spectrum model

14 Nonlinear RCM Compensation for SA-FBSAR － nonlinear RCM analytic formula

15 Nonlinear RCM Compensation for SA-FBSAR － nonlinear RCM analytical formula

16 Nonlinear RCM Compensation for SA-FBSAR － nonlinear RCM compensation method Fig.5 flow chart of nonlinear RCM compensation method for SA-FBSAR,

17 Simulation － Simulation － Parameters ParametersTransmitterReceiver Height (km)5143 velocity (m/s) azimuth beam width(degree) maximum steering angle(degree) depression angle (degree)3768 beam velocity(m/s) integration duration (s)0.43 pulse width (μs)2 central frequency of transmitting signal (GHz) 9.65 bandwidth of transmitting signal (MHz) 60 pulse repetition frequency(Hz)2500

18 Simulation － Simulation － Point scatterers (a) original point scatterers (b) without RCM compensation (d) with the proposed method (c) with RCMC Method in Ref[1] Ref[1]: X.Qiu, D. Hu and C. Ding, IEEE Geosci. Remote Sens. Lett., 4, , Fig.6 Imaging results of 15 point scatters

19 Simulation － Simulation － Point scatterers (a) error in range position (b) error in azimuth position

20 Simulation － Simulation － area target x y Fig. 7 Imaging results of area target (a) original area target (b) Without RCMC (c) With the proposed RCM compensation

21 Fig.8 two-dimensional resolution performance (a) Contour of ideal resolution cell’s area (unit: m 2 ) (b) target located at (500,100) (c) target located at (0,0)

22 Simulation From the above simulation results, we could find that: Uncompensated RCM could deteriorate imaging result severely, cause nonlinear distortion RCM compensation method designed for other FBSAR system could not compensate the nonlinear RCM, thus could not be applied to SA-FBSAR. The proposed RCM compensation method could effectively compensate the nonlinear RCM in SA-FBSAR, and all targets are arranged in their originally correct positions.

23 Conclusions & Further work RCM in SA-FBSAR not only depends on the target’s two- dimensional space location, but also varies with its range location nonlinearly. If not properly corrected, RCM would cause nonlinear distortion in the image and greatly degrade the imaging quality. We propose a two-dimensional nonlinear RCMC method for SA-FBSAR. The validity of the proposed method is verified.  Further improvement on resolution performance is under research

24 Thank you