Abstract
Azimuth multichannel (AMC) synthetic aperture radar (SAR) is an advanced technology that can prevent the minimum antenna area constraint and provide high-resolution and wide-swath SAR images. The calibration of phase imbalance is an important topic in the AMC SAR signal processing since it has a significant impact on the image quality. For one SAR image, the phase imbalance is usually considered as a constant. However, because of the attitude errors, antenna position errors, target elevation, target motion, and phase mismatch of the antenna pattern, the actual phase imbalance is time-varying in azimuth and space-varying in range. Although the space-time variation of phase imbalances is too tiny to make a little effect on the product quality, it is still meaning to study the variation. On the one hand, it is possible to quickly estimate the phase imbalance of the whole observing operation and eliminate the influences of target motion, on the phase imbalance. On the other hand, some parameters, such as motion, can be retrieved by the phase imbalance. This article first establishes the signal models between phase imbalances and attitude errors, antennal position errors, and target elevation. Then, the signal model is verified by some simulations based on the parameters of Gaofen-3 (GF-3). In addition, the phase imbalance of the real data acquired by GF-3 is processed. Finally, based on the procession results of GF-3 real data, this article makes some discussions and points out the direction for the future work.
Highlights
S INCE the first spaceborne synthetic aperture radar (SAR) was launched in 1978, SAR has been an effective means of earth observation with the excellent capability of working in all weather and all time
Based on the real data acquired by Gaofen-3 (GF-3), we proposed the correlation method in the 2-D frequency domain to estimate the phase imbalance, range sampling time imbalance (RSTI), and along-track baseline, in the former work [17]
If it is only to suppress the false targets in SAR images, it is not necessary to consider the space-time variation of the phase imbalance for the ultrafine strip-map (UFS) mode of GF-3 because it has been proved through simulations, when the phase imbalance is 10°, the intensity of the false targets is still lower than −50 dB [17]
Summary
S INCE the first spaceborne synthetic aperture radar (SAR) was launched in 1978, SAR has been an effective means of earth observation with the excellent capability of working in all weather and all time. Based on the real data acquired by Gaofen-3 (GF-3), we proposed the correlation method in the 2-D frequency domain to estimate the phase imbalance, range sampling time imbalance (RSTI), and along-track baseline, in the former work [17]. All these methods treat the phase imbalance as a constant without considering the time-varying in azimuth and the space-varying in range. SHANG et al.: SPACE-TIME VARIATION OF PHASE IMBALANCE FOR GF-3 AZIMUTH MULTICHANNEL MODE on the SAR images. Similar to the interferogram of ATI, the phase imbalance of the AMC SAR contains the motion information of the imaging scene.
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