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| Citation: | LI Zhongyu, GUI Liang, HAI Yu, et al. Ultrahigh-resolution ISAR micro-Doppler suppression methodology based on variational mode decomposition and mode optimization[J]. Journal of Radars, 2024, 13(4): 852–865. doi: 10.12000/JR24043
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Ultrahigh-resolution ISAR Micro-Doppler Suppression Methodology Based on Variational Mode Decomposition and Mode Optimization
DOI: 10.12000/JR24043
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Abstract
The imaging of aerial targets using Inverse Synthetic Aperture Radar (ISAR) is affected by micro-Doppler effects resulting from localized micromotions, such as rotation and vibration. These effects introduce additional Doppler frequency modulation into the echo, leading to spectral broadening. Under ultrahigh-resolution conditions, these micromotions interfere with the focusing process of subject scatterers, resulting in images with poor focus showing significantly reduced quality. Furthermore, micro-Doppler signals exhibit temporal variability and nonstationary characteristics, posing difficulties in their estimation and differentiation from the echo. To address these challenges, this paper proposes a nonparametric method based on Variational Mode Decomposition (VMD) and mode optimization to separate the echo of the subject from micro-Doppler components. This separation is achieved by utilizing differences in their respective time-frequency distributions. This methodology mitigates the effect of micro-Doppler signals on the echo and obtains imaging results of a drone with ultrahigh-resolution. The VMD algorithm is introduced and subsequently extended to the complex domain. The method entails the decomposition of the ISAR echo along the azimuth direction into several mode functions distributed uniformly across the Doppler sampling bandwidth. Subsequently, image entropy indices are employed to optimize the decomposition parameters and select the imaging modes. This ensures the effective suppression of micro-Doppler signals and preservation of the subject echo. Compared to existing methods based on Empirical Mode Decomposition (EMD) and Local Mean Decomposition (LMD), the proposed method exhibits superior performance in suppressing image blurring caused by micro-Doppler effects while ensuring complete retention of fuselage details. Furthermore, the effectiveness and advantages of the proposed method are validated through simulations and processing of ultrawideband microwave photonic data obtained from drone measurements. -
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References
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- Figure 1. Variation of the number of range cells for several typical targets with bandwidth
- Figure 2. Turntable model of ISAR
- Figure 3. ISAR geometric model of targets with micro-motion components
- Figure 4. STFT spectrogram and spectrum of the micro-Doppler signal
- Figure 5. Schematic diagram of the extended VMD
- Figure 6. Flow diagram of the proposed micro-Doppler suppression method
- Figure 7. Multi-point target layout and direct imaging diagram
- Figure 8. Comparison of the imaging results processed by various algorithms
- Figure 9. Comparison of the STFT spectrogram processed by various algorithms
- Figure 10. Comparison of simulated imaging results at different SNR
- Figure 11. Radar system and target diagram
- Figure 12. Comparison of the effects of different algorithms on the processing of measured data
- Figure 13. STFT spectrogram of the center point on the rotor after processing
- Figure 14. Azimuth residual phase and profile comparison of the center point on the rotor