Abstract
In view of the azimuth resolution of the helicopter-borne rotating array synthetic aperture radar (RoASAR) depending on the azimuth reconstruction angle and the sector distortion caused by the azimuth Deramp processing, this paper proposes an efficient helicopter-borne RoASAR high-resolution imaging algorithm based on two-dimensional (2-D) chirp-z transform (CZT). First, the high-order Taylor series expansion is performed on the slant range, and the accurate 2-D spectral expression of the point target is obtained by using the method of series reversion (MSR). Based on that, the space-variant characteristics of the range cell migration (RCM) terms are analyzed. After that, the space-variant RCM and the sector distortion effect caused by the azimuth Deramp processing are removed by using efficient 2-D CZT, thereby increasing the azimuth reconstruction angle and improving the azimuth resolution. The proposed algorithm is efficient without the interpolation operation, and it is easy to implement in real-time. Finally, the simulations are provided to verify the effectiveness of the proposed algorithm.
Highlights
Helicopter-borne rotating array synthetic aperture radar (RoASAR) is a novel radar imaging model and system, which is installed and operated on a helicopter platform, where the radar antenna is set on a rigid support at the tip of the helicopter rotor
To overcome the low-resolution shortcoming, the Omega-k imaging method is proposed in [11,12,13], but it has the great computation burden caused by the Stolt interpolation operation, and it is only applicable to the small imaging area near the center of the scene due to the range of spatial-variant characteristics of the tangential velocity
The detailed derivations of the proposed fast RoASAR imaging algorithm using the 2-D chirp-z transform (CZT) is provided, which mainly contains the following three steps: (1) the precise 2-D frequency analytic expression, (2) spatial-variant range cell migration (RCM) correction using an efficient, improved inverse CZT (ICZT), and (3) SAR image azimuth distortion caused by the Deramp operation compensated by the CZT
Summary
Helicopter-borne rotating array synthetic aperture radar (RoASAR) is a novel radar imaging model and system, which is installed and operated on a helicopter platform, where the radar antenna is set on a rigid support at the tip of the helicopter rotor. To overcome the low-resolution shortcoming, the Omega-k imaging method is proposed in [11,12,13], but it has the great computation burden caused by the Stolt interpolation operation, and it is only applicable to the small imaging area near the center of the scene due to the range of spatial-variant characteristics of the tangential velocity. To reduce the computational complexity, a novel imaging method based on the chirp-z transform (CZT) is proposed in [14,15], in which an efficient CZT is utilized to remove the range-azimuth coupling. This method ignores the azimuth sector distortion caused by azimuth Deramp operation.
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