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A Synthetic Bandwidth Method for High-Resolution SAR Based on PGA in the Range Dimension.

Li J, Chen J, Liu W, Wang P, Li C - Sensors (Basel) (2015)

Bottom Line: The synthetic bandwidth technique is an effective method to achieve ultra-high range resolution in an SAR system.Furthermore, an improved cut-paste method is proposed to combine the signals in the frequency domain.Imaging results based on both simulated and real data are presented to validate the proposed approach.

View Article: PubMed Central - PubMed

Affiliation: School of Electronic and Information Engineering, Beihang University, Beijing 100191, China. lijincheng_buaa@163.com.

ABSTRACT
The synthetic bandwidth technique is an effective method to achieve ultra-high range resolution in an SAR system. There are mainly two challenges in its implementation. The first one is the estimation and compensation of system errors, such as the timing deviation and the amplitude-phase error. Due to precision limitation of the radar instrument, construction of the sub-band signals becomes much more complicated with these errors. The second challenge lies in the combination method, that is how to fit the sub-band signals together into a much wider bandwidth. In this paper, a novel synthetic bandwidth approach is presented. It considers two main errors of the multi-sub-band SAR system and compensates them by a two-order PGA (phase gradient auto-focus)-based method, named TRPGA. Furthermore, an improved cut-paste method is proposed to combine the signals in the frequency domain. It exploits the redundancy of errors and requires only a limited amount of data in the azimuth direction for error estimation. Moreover, the up-sampling operation can be avoided in the combination process. Imaging results based on both simulated and real data are presented to validate the proposed approach.

No MeSH data available.


Imaging results based on collected real SAR data: (a) imaging result of sub-band signal; (b) imaging result of reconstruction with relative calibration; (c) imaging result of reconstruction of first-order TRPGA; (d) imaging result of reconstruction of two-order TRPGA; (e) range profile of point target in (b,c,d).
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f9-sensors-15-15339: Imaging results based on collected real SAR data: (a) imaging result of sub-band signal; (b) imaging result of reconstruction with relative calibration; (c) imaging result of reconstruction of first-order TRPGA; (d) imaging result of reconstruction of two-order TRPGA; (e) range profile of point target in (b,c,d).

Mentions: Simulations are first performed to demonstrate the effectiveness of the first two steps of the proposed method. The filter error is chosen according to the real error calculated from the target point circled in Figure 9a. The timing error between the sub-bands is 4.05 ns and 1.2828 ns, respectively, identical to the timing deviation extracted from the internal calibration data. Figure 8a shows the compressed result when the standard matched filtering is applied to the simulated sub-band data directly. It can be seen that the impulse response function has deteriorated seriously with the side lobes raised and asymmetric, which means that impulse response width (IRW), peak side-lobe ratio (PSLR) and integrated side-lobe ratio (ISLR) cannot meet the imaging requirement any more. After error correction using the first step of the proposed method, the IRW becomes 0.443 m and the PSLR is 13.26 dB, as shown by the solid line. As for the performance of the combination processing, we consider three cases: Case 1, ignoring timing error; Case 2, applying the conventional cut-paste method; and Case 3, implementing the improved cut-paste technique. The blue line represents the construction result without compensation of the timing errors. The timing deviations between the sub-bands split the compressed pulse into several peaks, conforming to the analysis given by Equation (13). After removal of the time deviations, the reconstructed pulse employing the conventional cut-paste method is shown by the red line in Figure 8b. The rise and asymmetry of the side lobes compared with the result processed by the improved cut-paste combination method is obvious, as shown in the enlarged profile. The ideal and measured values of IRW, PSLR and ISLR are listed in the upper part of Table 2. The IRW and PSLR implementing the proposed combination approach are 0.153 m and 13.25 dB, respectively. The consistency between the ideal values and the measured ones indicates that the signals from the three sub-bands have been combined coherently.


A Synthetic Bandwidth Method for High-Resolution SAR Based on PGA in the Range Dimension.

Li J, Chen J, Liu W, Wang P, Li C - Sensors (Basel) (2015)

Imaging results based on collected real SAR data: (a) imaging result of sub-band signal; (b) imaging result of reconstruction with relative calibration; (c) imaging result of reconstruction of first-order TRPGA; (d) imaging result of reconstruction of two-order TRPGA; (e) range profile of point target in (b,c,d).
© Copyright Policy
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4541834&req=5

f9-sensors-15-15339: Imaging results based on collected real SAR data: (a) imaging result of sub-band signal; (b) imaging result of reconstruction with relative calibration; (c) imaging result of reconstruction of first-order TRPGA; (d) imaging result of reconstruction of two-order TRPGA; (e) range profile of point target in (b,c,d).
Mentions: Simulations are first performed to demonstrate the effectiveness of the first two steps of the proposed method. The filter error is chosen according to the real error calculated from the target point circled in Figure 9a. The timing error between the sub-bands is 4.05 ns and 1.2828 ns, respectively, identical to the timing deviation extracted from the internal calibration data. Figure 8a shows the compressed result when the standard matched filtering is applied to the simulated sub-band data directly. It can be seen that the impulse response function has deteriorated seriously with the side lobes raised and asymmetric, which means that impulse response width (IRW), peak side-lobe ratio (PSLR) and integrated side-lobe ratio (ISLR) cannot meet the imaging requirement any more. After error correction using the first step of the proposed method, the IRW becomes 0.443 m and the PSLR is 13.26 dB, as shown by the solid line. As for the performance of the combination processing, we consider three cases: Case 1, ignoring timing error; Case 2, applying the conventional cut-paste method; and Case 3, implementing the improved cut-paste technique. The blue line represents the construction result without compensation of the timing errors. The timing deviations between the sub-bands split the compressed pulse into several peaks, conforming to the analysis given by Equation (13). After removal of the time deviations, the reconstructed pulse employing the conventional cut-paste method is shown by the red line in Figure 8b. The rise and asymmetry of the side lobes compared with the result processed by the improved cut-paste combination method is obvious, as shown in the enlarged profile. The ideal and measured values of IRW, PSLR and ISLR are listed in the upper part of Table 2. The IRW and PSLR implementing the proposed combination approach are 0.153 m and 13.25 dB, respectively. The consistency between the ideal values and the measured ones indicates that the signals from the three sub-bands have been combined coherently.

Bottom Line: The synthetic bandwidth technique is an effective method to achieve ultra-high range resolution in an SAR system.Furthermore, an improved cut-paste method is proposed to combine the signals in the frequency domain.Imaging results based on both simulated and real data are presented to validate the proposed approach.

View Article: PubMed Central - PubMed

Affiliation: School of Electronic and Information Engineering, Beihang University, Beijing 100191, China. lijincheng_buaa@163.com.

ABSTRACT
The synthetic bandwidth technique is an effective method to achieve ultra-high range resolution in an SAR system. There are mainly two challenges in its implementation. The first one is the estimation and compensation of system errors, such as the timing deviation and the amplitude-phase error. Due to precision limitation of the radar instrument, construction of the sub-band signals becomes much more complicated with these errors. The second challenge lies in the combination method, that is how to fit the sub-band signals together into a much wider bandwidth. In this paper, a novel synthetic bandwidth approach is presented. It considers two main errors of the multi-sub-band SAR system and compensates them by a two-order PGA (phase gradient auto-focus)-based method, named TRPGA. Furthermore, an improved cut-paste method is proposed to combine the signals in the frequency domain. It exploits the redundancy of errors and requires only a limited amount of data in the azimuth direction for error estimation. Moreover, the up-sampling operation can be avoided in the combination process. Imaging results based on both simulated and real data are presented to validate the proposed approach.

No MeSH data available.