Xinhua Mao

Comparative Study of Rma and Pfa on Their Responses to Moving Target

The synthetic aperture radar (SAR) signatures of moving target are the basis of ground moving target indication and imaging (GMTI&Im) in the framework of SAR systems. However, previous studies are mainly based on the 2-D separable SAR processing, and little work has been done to investigate the signatures of moving target after the application of a particular flne resolution SAR image formation algorithm. In this paper, we derive the image spectrum of moving target after two representative flne resolution SAR image formation algorithms, i.e., the range migration algorithm (RMA) and polar format algorithm (PFA), respectively. Based on the spectrum derived, detailed analysis on the SAR signatures of moving target, including the geometric displacement, residual range migration, and defocusing efiect in both the range and azimuth dimensions are performed. The presented work might be helpful when considering a SAR system with the capability of ground moving target indication and imaging (GMTI&Im).

Response of polar format algorithm to moving target with consideration of wavefront curvature

The synthetic aperture radar (SAR) signatures of moving target are the basis of ground moving target detection and imaging (GMTI&Im). However, previous studies are mainly focused on the influence of targets motion on phase history; and little work has been done to investigate the signatures of moving target after the application of a particular SAR image formation algorithm. In this paper, we derive the image spectrum of moving target after polar format algorithm (PFA) processing. Based on this image spectrum, detailed analysis on the SAR signatures of moving target, including the geometric displacement, residual range migration, range and azimuth defocusing are performed. Simulation results validate the theoretical analysis.

Application of the frequency-domain synthetic bandwidth approach in Polar Format Algorithm

The problem of wide bandwidth management in current ultra-high resolution spotlight SAR systems could be solved by adopting stepped chirps and utilizing synthetic bandwidth approach. High resolution SAR image formation is a non-separable 2-D impulse compression processing, so the synthetic bandwidth procedure should be modified correspondingly with the image formation algorithm adopted. This paper demonstrates the application of frequency-domain synthetic bandwidth approach in SAR Polar Format Algorithm (PFA). The problem of motion compensation between the subpulses within a burst is discussed, and the signal processing flows are investigated in detail. The presented approach is validated by point target simulation.

A new formulation of polar format algorithm for bistatic spotlight SAR

In this paper, a new interpretation of the polar format algorithm (PFA) for bistatic spotlight synthetic aperture radar (SAR) imaging is presented. From the viewpoint of two-dimensional decoupling, we examine the commonly adopted implementation of the PFA, i.e., the separable 1-D range and azimuth resampling procedures for their roles in range cell migration (RCM) correction, respectively. It is shown that the range resampling corrects for the RCM associated with the down-range coordinate of target, while the azimuth resampling compensates for the RCM associated with the cross-range coordinate of target. The presented work provides a new perspective on the mechanism of RCM correction in PFA.

Polar format algorithm wavefront curvature compensation under arbitrary radar flight path

An improved space-variant post-filtering approach to compensate the wavefront curvature effect in polar format imagery is presented in this paper, which is based on exploiting the endomorphism property of the polar format transformation. The main contribution of this paper is the construction of filter, which provides an accurate and general solution to wavefront curvature compensation. Point target simulation has validated the new approach.

Wavefront curvature correction for missile borne spotlight SAR polar format image

The polar format algorithm (PFA) for spotlight synthetic aperture radar (SAR) is influenced by wavefront curvature error. The previous wavefront curvature compensation methods are all assumed that the height of the radar is constant, these compensation methods cannot be directly applied to the case of missile borne SAR where the platform always has large dive angle. In this paper, the precise expression of wavefront curvature phase error in the frequency domain of missile borne SAR is derived. Image domain post-processing steps, including space-variant filtering and geometric distortion correction, are employed to compensate the quadratic and linear phase error terms. This method further improves the precision of wavefront curvature compensation. Simulation results validate the theoretical analysis.

A fast polar format algorithm based on variable PRF for bistatic SAR

Polar Format Algorithm (PFA), which is a classic algorithm for bistatic SAR imaging, has important significance in spotlight bistatic SAR system. In this paper, a fast polar format algorithm based on variable PRF for bistatic SAR is proposed. This algorithm can correct range cell migration (RCM) without high-precision interpolation, which can improve the computation efficiency. Point target simulation validates the algorithm.

Two-dimensional autofocus for SAR range migration algorithm

In this paper, the analytical structure of residual 2D phase error in RMA imagery is investigated. By incorporating the inherent phase structure knowledge, an efficient 2-D autofocus algorithm is proposed. The new approach estimates the 2-D phase errors in semi-blind manner, it offers clear advantages in both computational efficiency and estimation accuracy as compared with conventional blind 2-D autofocus algorithms.

CFAR detection of moving target for Monopulse-SAR based on statistical analysis of complex monopulse ratio

An efficient approach to achieve ground moving target indication (GMTI) for synthetic aperture radar (SAR) is to use the Monopulse-SAR system. This paper examines the statistics of complex monopulse ratio (CMR) for SAR/GMTI model when complex Gaussian clutter-plus-noise is considered. The two dimensional probability density function (pdf) of CMR is analyzed in detail. An automatic constant false-alarm rate (CFAR) detector with the probability of false alarm given in a closed-form for moving targets is provided and extended to a multi-CMRD form to further improve the final detection performance. Experimental results are presented to examine the detection performance and validate the theoretical analysis.

The application of the principle of chirp scaling in processing stepped chirps in spotlight SAR

A new approach for processing stepped chirps in spotlight SAR is presented in this manuscript, which is based on exploiting the principle of chirp scaling (PCS). In particular the PCS is integrated in a Polar Format Algorithm (PFA), obtaining a more efficient solution compared with the existing interpolation based technique. The main contribution is the implementation of the azimuth scaling with the bandwidth synthesis embedded in, and it is developed dedicatedly for dealing with stepped chirps. The signal processing flow is investigated in detail, with no interpolations but only FFTs and complex multiplications involved, and point target simulation has validated the new approach based on PCS is feasible and more efficient than the existing interpolation based approach.