The Space-Time Variation of Phase Imbalance for GF-3 Azimuth Multichannel Mode

Abstract

Azimuth multichannel (AMC) synthetic aperture radar (SAR) is an advance 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 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. Even though the space-time variation of phase imbalances is too tiny to make 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, etc. on the phase imbalance. On the other hand, some parameters, such as motion, can be retrieved by phase imbalance. This paper 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 paper makes some discussions and points out the direction for the future work.

Phase Imbalance Analysis of GF-3 Along-Track InSAR Data for Ocean Current Measurement

“…The phase imbalances between channels for ATI-SAR are caused by many factors, such as the radar electronic system, the phase mismatch of the antenna pattern, satellite attitude errors, antenna electronic miss-pointing, antenna phase center position errors, sampling time delay error, and target elevation [13]. Therefore, the interferometric phase directly obtained from the two SAR images cannot truly reflect the Doppler information of the radar irradiation area.…”

“…The phase imbalance between channels in the case of squint imaging caused by baseline error can be expressed as [13,24]:…”

“…It is the SAR satellite with the most imaging modes in the world. Besides, GF-3 also carried out multiple ATI test missions in 2018 and 2019, imaging by dual-receiving, and obtained two fine strip-map (FSI) mode images of the same scene with a time lag of milliseconds, which used an effective along-track antenna separation of 3.75 m. We analyzed the dualchannel space-time variability of phase imbalance in GF-3 ultra-fine strip-map (UFS) mode through simulation and a large amount of actual data [13], considering that the dual-channel space-time variability of phase imbalance is attributed to the antenna phase position error and phase mismatch of the antenna pattern.…”

Phase Imbalance Estimation for Azimuth Multi-Channel ScanSAR System

“…The image quality of the azimuth multi-channel system depends on ambiguity suppression technologies, including nonuniform signal reconstruction [15] [16] and channel imbalance calibration [17]- [22]. The inconsistency of multichannel hardware facilities will lead to channel mismatch, such as central electronic equipment, antenna array, satellite platform, and so on.…”

“…Moreover, Jin compared the TDCM with two subspace methods and pointed out that although the computational load of TDCM is lowest, it works worse than the subspace methods, for the deviation is cumulative when the phase error accumulates [20]. Shang proposed the correlation method in the two-dimensional frequency domain to estimate channel imbalance in [21] and analyzed the space-time variation of the channel phase error [22]. However, the above methods are all proposed for the multi-channel system in stripmap operation.…”