Abstract
In a multichannel geosynchronous spaceborne–airborne bistatic synthetic aperture radar (GEO-SA-BiSAR) system, the airborne receiver can obtain high-resolution microwave images with good signal-to-noise ratios (SNRs) by passively receiving echoes from the desired area. Since the Doppler modulation and range history of a moving target are obviously different from a stationary target, a signal geometry model for moving targets in multichannel GEO-SA-BiSAR is established in this paper. According to simulation results, the along track velocity introduces target defocusing in azimuth, and the slant range velocity mainly causes multiple false targets. To resolve these problems, a modified multichannel reconstruction method in azimuth channel GEO-SA-BiSAR is proposed according to the azimuth multichannel impulse response of the imaged moving target. Before azimuth multichannel raw data combination, both spatial-variant range cell migration correction (RCMC) and azimuth nonlinear chirp scaling (ANLCS) should be performed to reduce the influence of the range offset and lower the Doppler bandwidth of the whole raw data, respectively. Afterward, a novel azimuth multichannel reconstruction algorithm is carried out via the modified reconstruction matrix based on the estimated target velocity. The target slant range velocity estimation is implemented by introducing the signal intensity ratio (SIR). Compared with the conventional method for the stationary target to handle the raw data of the moving target, the false targets could be obviously suppressed by using the proposed approach. Imaging results on both simulated point and distributed scene targets validate the proposed multichannel reconstruction approach.
Highlights
Synthetic aperture radar (SAR) can get microwave images of the desired scene under all weather conditions, day and night [1]
The introduced signal intensity ratio (SIR) Γ varying with the estimated slant range velocity is shown in Figure 12, and all SIRs reach the maximum value only when the accurate slant range velocity is adopted for azimuth multichannel reconstruction
The operating pulse repetition frequency (PRF) of a GEO-SA-BiSAR system is less than the wide Doppler bandwidth determined by the airborne receiver, which leads to azimuth spectrum aliasing
Summary
Synthetic aperture radar (SAR) can get microwave images of the desired scene under all weather conditions, day and night [1]. If azimuth multichannel reconstruction and imaging approaches for stationary scenes were adopted to handle the echoes of moving targets, imaging quality would be seriously reduced To resolve this issue, the geometry model of the moving target in GEO-SA-BiSAR is analyzed in this paper, and the effects of the target velocity including the along track and slant range components on the focusing quality are analyzed. For a GEO SAR with a high orbit, a fourth-order approximation of RT(t) is usually modeled and established to accurately estimate the actual slant range between the GEO SAR system and the target with a long synthetic aperture time [28], and it is written as RT(t) ≈ R1T + k1Tt + k2Tt2 + k3Tt3 + k4Tt4. Combining (6) and (12) together, the total slant range can be rewritten as follows: RT(t) + Rm(t) ≈
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
