Abstract
Azimuth multichannel (AMC) synthetic aperture radar (SAR), which contains multiple receiving antennas along the azimuth, can prevent the minimum antenna area constraint and provide high-resolution and wide-swath (HRWS) SAR images. Channel calibration and along-track baseline estimation are important topics in an AMC SAR system, since they have a great impact on image quality. Based on the signal model for stationary target of AMC SAR, this paper first analyses the influence of the along-track baseline and channel imbalances on SAR images by simulation. Then, a novel method to simultaneously estimate the along-track baseline, phase imbalance and range sample time imbalance (RSTI) based on the azimuth cross-correlation in the two-dimensional frequency domain is addressed. In addition, with the help of simulations and real data acquired by Gaofen-3 (GF-3), the effectiveness of this method is verified by comparing with some existing methods. Finally, this paper analyzes the estimation accuracy of this method under different scenarios and signal-to-noise ratios (SNRs), and points out the direction for future research.
Highlights
Since the first spaceborne synthetic aperture radar (SAR) SEASAT was launched in 1978, SAR has been an effective means of earth observation with an excellent capability to work in all-weather and all-time
The method proposed by this paper has been confirmed by processing the simulation and real data, and the real data of GF-3 in ultrafine stripmap (UFS) mode are used to illustrate the estimation results in different scenarios
Taking the 20th image in Figure 11 as an example, the azimuth spectrums of the two channel signals after amplitude imbalance correction are shown in Figure 15a, where the ordinate is the normalized spectrum and the abscissa is the beam width corresponding to the imaging scene
Summary
Since the first spaceborne synthetic aperture radar (SAR) SEASAT was launched in 1978, SAR has been an effective means of earth observation with an excellent capability to work in all-weather and all-time. A method for estimating the along-track baseline is proposed, and its reliability has been verified by simulation and real data required by GF-3 in UFS mode. Based on the azimuth cross-correlation in the two-dimensional frequency domain, this paper proposed a novel method to simultaneously estimate the along-track baseline and channel imbalances including phase imbalance and RSTI without estimating the Doppler centroid. Using the real data acquired by GF-3 in UFS mode, the estimation results of this method under different scenarios and SNR are given, and the images before and after channel imbalances correction are compared. After describing and analyzing the channel imbalances and along-track baseline, Section 3 proposes the general estimation method based on the interferometric phase in the two-dimensional frequency domain.
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