A Hybrid SAR/ISAR Approach for Refocusing Maritime Moving Targets with the GF-3 SAR Satellite
Abstract
:1. Introduction
- We use the DCT algorithm in the IROPE method to improve the SNR of the data and render the subsequent estimation more accurate, which also makes the data more consistent with the model of the ROPE method.
- We avoid the averaging of phase vectors with different linear components and maximize the accuracy of the phase compensation by using the circular shift of the prominent point in each range bin to zero frequency to rationalize the initialization of the Doppler center.
- Moreover, better estimates are obtained through iteration. Multiple iterative algorithms improve the SNR, which further improves the accuracy of the Doppler circular shift and the estimation of phase error.
- The proposed method focuses the blurred images well and exhibits the superiority of robustness, reduced sidelobes, and suitability for various phase errors, which does not require time-consuming parameter adjustment procedures to achieve improved performance and allows a long coherent processing interval.
2. Moving Signal Model
2.1. SAR Signal Model
2.1.1. Analysis of Moving Echo Characteristics
2.1.2. Analysis of Moving Target Response
2.2. ISAR Signal Model
3. Improved Rank-One Phase Estimation Algorithm
3.1. Problems of the Rank-One Phase Estimation Algorithm
3.2. Principle of IROPE
Algorithm 1: The IROPE algorithm for phase compensation |
Input: The range-aligned echo , , , number of iterations l, threshold value T |
1: I. Preliminary Phase Compensation |
2: for |
3: |
4: end |
5: IV. Iteration |
6: for (Image entropy is further applied to control the iteration process) |
7: II. Two-step Convergence |
8: III. Circular Shifting |
9: while > T |
10: for |
11: Update calculated by Equation (19) |
12: end |
13: for |
14: Update calculated by Equation (19) |
15: end |
16: |
17: end while |
18: |
19: |
20: end |
Output: Compensated range-Doppler echo , phase error |
3.3. Performance of IROPE
3.4. The Whole Process of the Refocusing Method
4. Experiments and Performance Comparisons
4.1. Results of Spotlight Simulation
4.1.1. Ship Target with Velocity and Acceleration
4.1.2. Ship target with Translation and Rotation
4.2. Spaceborne SAR Data Experiments
4.2.1. Real Data Corrupted by Phase Error
4.2.2. Intrinsically Corrupted Real Data
5. Discussion
6. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Parameter | Value |
---|---|
Mode | Spotlight |
Radar Center Frequency (GHz) | 5.4 |
Wavelength (m) | 0.0555 |
Bandwidth (MHz) | 50 |
Azimuth Resolution (m) | 1.5 |
Range Resolution (m) | 2.6562 |
PRF (Hz) | 3125 |
Upsampled PRF (Hz) | 9950.2398 |
Upsampled Doppler Bandwidth (Hz) | 6188.7356 |
Slant-Range (m) | 1,067,731.2395 |
Synthetic Aperture Time (s) | 2.3342 |
SAR Velocity (m/s) | 7500 |
squint angle () | 0 |
Parameter | Value |
---|---|
Mode | Spotlight |
Radar Center Frequency (GHz) | 5.400012 |
Bandwidth (MHz) | 240.000000 |
Azimuth Resolution (m) | 1 |
Range Resolution (m) | 0.6 |
PRF (Hz) | 3125.164062 |
Synthetic Aperture Time (s) | 8.58 |
Satellite Velocity (m/s) | 7570.962970 |
IQEMs | Corrupted image | MD | ROPE | IROPE |
---|---|---|---|---|
Contrast increase | −4.08 | −3.86 | −0.47 | −0.09 |
Entropy reduction | −1.69 | −1.58 | −0.21 | 0.08 |
IP increase | −20.01 | −16.82 | −2.58 | 0.77 |
Ship | Ship1 | Ship2 | Ship3 | ||||||
---|---|---|---|---|---|---|---|---|---|
IQEMs | MD | ROPE | IROPE | MD | ROPE | IROPE | MD | ROPE | IROPE |
Contrast increase | 0.42 | 0.23 | 0.49 | 0.01 | 0.01 | 0.02 | 0.23 | −0.12 | 0.93 |
Entropy reduction | 0.40 | 0.25 | 0.47 | 0.16 | 0.15 | 0.24 | 0.20 | −0.02 | 0.47 |
IP increase | 6.08 | 5.21 | 6.78 | 3.05 | 2.60 | 4.82 | 4.18 | 1.53 | 4.69 |
Works | Schemes | Application | Phase Error Estimation | Accuracy |
---|---|---|---|---|
MD | Sub-aperture correlation | Limited | Unsatisfactory | Unsatisfactory |
ROPE | Two-step convergence | Limited | Unsatisfactory | Unsatisfactory |
IROPE | Preprocessing+ Circular Shifting +Two-step convergence+Iteration | Wide | Good | Good |
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Yan, Z.; Zhang, Y.; Zhang, H. A Hybrid SAR/ISAR Approach for Refocusing Maritime Moving Targets with the GF-3 SAR Satellite. Sensors 2020, 20, 2037. https://doi.org/10.3390/s20072037
Yan Z, Zhang Y, Zhang H. A Hybrid SAR/ISAR Approach for Refocusing Maritime Moving Targets with the GF-3 SAR Satellite. Sensors. 2020; 20(7):2037. https://doi.org/10.3390/s20072037
Chicago/Turabian StyleYan, Zhishuo, Yi Zhang, and Heng Zhang. 2020. "A Hybrid SAR/ISAR Approach for Refocusing Maritime Moving Targets with the GF-3 SAR Satellite" Sensors 20, no. 7: 2037. https://doi.org/10.3390/s20072037
APA StyleYan, Z., Zhang, Y., & Zhang, H. (2020). A Hybrid SAR/ISAR Approach for Refocusing Maritime Moving Targets with the GF-3 SAR Satellite. Sensors, 20(7), 2037. https://doi.org/10.3390/s20072037