Yanyan Zhang

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Zhang

First Name

Yanyan

ORCID

0000-0002-3497-4474

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Publications 1 - 7 of 7

An Advanced Interferometric Baseline Estimation Method (IBEM) for Spaceborne Bistatic SAR
Zhang, Yanyan; Li, Junfeng; Lu, Pingping; et al. (2024)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Spaceborne bistatic synthetic aperture radar (BiSAR) employs single-pass cross-track interferometry (XTI) to invert digital elevation models (DEMs) of target areas. However, the accuracy of the inverted DEM is affected by various factors, especially interferometric baseline estimation. To this end, this article proposes an advanced interferometric baseline estimation method (IBEM) for spaceborne BiSAR. First, the IBEM compensates for the time synchronization deviation of BiSAR systems using the pulse exchange phase synchronization method. Subsequently, the time, position, and velocity vectors of satellites are input into a high-precision orbit propagator to derive the state vectors at the imaging time. Leveraging these state vectors, the interferometric baseline is calculated with the main satellite that transmits radar signals as the origin of the coordinate system. Eventually, interferometric baseline estimation and DEM generation are performed based on two sets of data from the LuTan-1 (LT-1) BiSAR system, and the generated DEMs are compared with the external reference DEM to evaluate the performance of the IBEM and the LT-1 system. Results indicate that the proposed IBEM can accurately estimate the interferometric baseline and has extensive application prospects in future spaceborne multibaseline Interferometric SAR missions.
New Insights Into Alternating Transmitting Mode (ATM) for Bistatic Multichannel SAR
Zhang, Yanyan; Lu, Pingping; Wang, Robert (2024)
IEEE Transactions on Geoscience and Remote Sensing
The bistatic synthetic aperture radar (BiSAR) employs the alternating transmitting mode (ATM) to capture multidimensional scattering information of the target. However, the drawback of the ATM lies in doubling the pulse repetition frequency (PRF) and reducing the echo window (i.e., swath width), consequently limiting the high-resolution and wide-swath (HRWS) imaging capabilities of BiSAR. To achieve HRWS imaging, the article proposes new insights into the ATM of bistatic multichannel synthetic aperture radar (SAR). First, multichannel signal models containing time and phase synchronization deviations are established for BiSAR. Then, the imaging mode, clock synchronization scheme, and imaging method to achieve HRWS imaging are detailed. Finally, a group of system parameters for the HRWS imaging of the ATM is designed based on the LuTan-1 (LT-1) BiSAR system, and the synchronization and imaging simulations of the ATM are conducted using the data of the LT-1. Simulation results demonstrate that the ATM can achieve the HRWS imaging mode of 3 m/60 km. In short, these new insights pave the way for the HRWS imaging of distributed SAR.
An Advanced Multiaperture Reconstruction Method for Distributed Array SAR
Zhang, Yanyan; Lu, Pingping; Liu, Lizhi; et al. (2024)
IGARSS 2024 - 2024 IEEE International Geoscience and Remote Sensing Symposium
Multiaperture echo signals collected by distributed array SAR can be reconstructed to realize High-Resolution and Wide-Swath (HRWS) imaging. To achieve the HRWS imaging of distributed SAR, an advanced Azimuth Multi-Aperture Reconstruction (AMAR) method is put forward for the first time. First, to eliminate the trajectory offset of distributed SAR, the first-order baseline deviation, second-order baseline deviation and azimuth space variation error are compensated in turn for the calibrated and undersampled echo signals, and the echoes containing distorted azimuth ambiguity can be obtained. Second, the distortion of ambiguity is corrected by range decompression, anti-migration correction, etc. Finally, the echoes satisfying the Nyquist theorem are derived by the AMAR of Train formation, and the bistatic SAR imaging is performed. In addition, some simulations are conducted to evaluate the performance of the proposed method, and the results demonstrate that the method can achieve AMAR and HRWS imaging of distributed array SAR.
Demonstration of Phase-Preserving Synchronization RFI Suppression for L-Band Spaceborne Bistatic Interferometric SAR
Zhang, Yanyan; Li, Junfeng; Lu, Pingping; et al. (2024)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Spaceborne bistatic synthetic aperture radar (BiSAR) systems utilize an intersatellite link to achieve phase synchronization. However, radio frequency interference (RFI) from communication satellites and ground-based radars often contaminates the synchronization signal, leading to inaccuracies in the inverted digital elevation model (DEM). Therefore, this article puts forward an advanced phase-preserving synchronization RFI suppression method and validates it using data from an L-band BiSAR system, LuTan-1 (LT-1). The method involves detecting and locating RFI within a monopulse synchronization signal, and the signal at the estimated RFI position is removed to obtain a preprocessed signal. Then, based on the preprocessed signal and the RFI model, RFI is estimated using a gradient-based approach. Finally, the estimated RFI is subtracted from the monopulse signal to obtain the desired signal. In addition, synchronization RFI suppression and DEM generation experiments are performed on the LT-1 data to verify the proposed method. Experimental results demonstrate that the method effectively suppresses synchronization RFI and improves DEM accuracy, and it has extensive application prospects in future low-band distributed interferometric synthetic aperture radar missions.
An Innovative Link-Free Permanent-C (LFPC) Phase Synchronization Scheme for Distributed SAR
Zhang, Yanyan; Lu, Pingping; Wang, Robert (2023)
IEEE Geoscience and Remote Sensing Letters
The distributed multiple-input-multiple-output synthetic aperture radar (MIMO-SAR) system composed of numerous separated transmitters and receivers can realize multiangle imaging, cross-and along-track interferometry through their high-precision cooperation. However, phase synchronization is a major factor affecting the cooperation of distributed MIMOSAR. As such, this letter proposes a Link-Free Permanent-C (LFPC) phase synchronization scheme for the first time. The designed system framework, basic principle, and error model of the scheme are described, and some simulations are performed to evaluate the synchronization accuracy of the LFPC scheme. The results demonstrate that the LFPC scheme has a frequency stability of 10(-15) when SNR >= 50 dB, and it is a candidate for the future distributed SAR mission.
A Doppler Frequency Estimation Method for Improved Spaceborne Bistatic SAR Synchronization
Zhang, Yanyan; Frey, Othmar; Lu, Pingping (2025)
IGARSS 2025 - 2025 IEEE International Geoscience and Remote Sensing Symposium
In the pulse-exchange phase synchronization scheme, as employedin the LuTan-1 (LT-1) spaceborne bistatic syntheticaperture radar (SAR) system, coarse knowledge of the satelliteorbits reduces the accuracy of the phase synchronization,as unknown residual relative motion affects the estimationaccuracy of the Doppler frequency. In this paper, we proposea synchronization-signal-driven method to estimate theDoppler frequency, and we show that the method improvesthe synchronization accuracy of the LT-1 data. First, the LT-1 data used for the experiments are introduced. Second, theproposed Doppler frequency estimation method is described.Finally, the relative velocity and Doppler frequency betweenthe two satellites are estimated based on the LT-1 data and theproposed method. The results show that the proposed methodaccurately estimates the Doppler frequency and improves theaccuracy of phase synchronization.
RFI Suppression Scheme for Complicated Low-Rank Violation Cases
Li, Junfeng; Cai, Yonghua; Zhang, Yanyan; et al. (2024)
IEEE Transactions on Geoscience and Remote Sensing
With the growing scarcity of spectrum resources, frequency sharing among different systems is becoming quite common, which causes radio frequency interference (RFI) to normal synthetic aperture radar (SAR) applications. Recently, in the RFI suppression field, algorithms based on the low-rank property (LRP) assumption have become a popular research topic. However, this assumption is not valid in complicated cases, especially when there are a wide variety of RFIs. To address this problem, in this article, factors that affect the LRP are studied through theoretical analysis and simulation verification, a general RFI model is established to fit complicated cases, and an advanced RFI suppression scheme based on LRP restoration (LRPR) is proposed. The LRPR scheme has three steps. The first step is RFI localization, which captures the rough profile of the RFI in the time-frequency domain for RFI spectrum separation and extraction. The second step is RFI clustering, in which a novel similarity evaluation metric and corresponding two-step clustering algorithm are designed. The final step is RFI suppression. Operations for LRP recovery in each RFI group are proposed, and consequently, classical low-rank approximation methods are applied for RFI suppression. The simulation results for various types of RFI show the robustness and performance improvement of the proposed scheme. In addition, in LuTan-1 data processing, the proposed scheme outperforms classical algorithms in both intensity image recovery and phase preservation.

Publications 1 - 7 of 7

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