Gaohuan Lv

Ground Moving Target Indication in SAR Images by Symmetric Defocusing

A new algorithm is presented to indicate ground moving targets in synthetic aperture radar images. Two filters, which differ only in the signs of the phase responses, are used to defocus the complex image respectively. In the two defocused images, each stationary target is blurred to the same extent, but each moving target is blurred to different extents. Therefore, moving targets can be indicated by the patch-by-patch sharpness comparison of the two defocused images. The results of the simulated and real data show that this algorithm is effective and efficient.

Ground Moving Target Indication in SAR Images With Symmetric Doppler Views

A new algorithm is presented to indicate ground moving targets in synthetic aperture radar (SAR) images. Two symmetric SAR images, one is referred to as a positive Doppler view and the other as a negative Doppler view, are generated by refocusing the positive Doppler plane and the negative Doppler plane, respectively. In the two Doppler views, the backgrounds have the same intensity except that their azimuth resolution becomes half of that of the original image, but the moving targets appear at different positions and have different intensities due to their different Doppler contents arising from nonzero Doppler centroid caused by across-track motion. Therefore, moving targets can be indicated by the patch-by-patch intensity comparison of the two Doppler views. The results of the simulated and real data confirm that this algorithm is effective and efficient.

Moving-Target Velocity Estimation in a Complex-Valued SAR Imagery

In the ground moving target indication with synthetic aperture radar (SAR) community, algorithms used to estimate the velocity of a detected moving target are important because they are relative to the topics about refocusing and azimuth displacement correction. The velocity is regarded as a vector with two components, one in azimuth and one in range direction, and new algorithms aiming at estimating the two components are proposed and verifled. The range velocity estimator transforms a detected patch containing a moving target to range Doppler domain by using the 1-D fast Fourier Transform in each range bin to achieve its range Doppler locus. The slope of the range Doppler locus is computed by using the Radon Transform on the range Doppler plane and the range velocity component is worked out according to radar system parameters and the slope value. Two estimators are proposed to compute the azimuth velocity component. One is based on symmetric defocusing in Doppler domain, the other is based on phase gradient in wave-number domain. Experiments conflrm the efiectiveness of the estimators by using simulated and fleld data.

Synthetic aperture radar based ground moving target indicator using symmetrical Doppler rate matched filter pairs

A new scheme for detection of moving targets and estimation of the azimuth velocity components in a single complex-valued synthetic aperture radar (SAR) imagery is presented in this paper based on the symmetric Doppler rate matched (SDRM) filter pairs. An SDRM filter pair processes a given SAR imagery and achieves two defocused SAR images that have the same defocused background but different defocused moving targets, and then by comparing the sharpness of the two images, the moving targets are determined adaptively and automatically. The azimuth velocity estimator utilizes an SDRM filter pair bank to get azimuth velocity of detected targets. Experiments using real SAR data and simulations confirmed the effectiveness of the proposed scheme.

Optical moving target indicator for synthetic aperture radar images

An optical indicator is designed to detect the moving targets in complex-valued synthetic aperture radar (SAR) images and estimate their azimuth velocity components. The indicator consists of two subsystems, and each of them is composed of one phase-only filter and two cylindrical lenses. The subsystems refocus the SAR image by changing the parameters of the phase-only filters to get two refocused images in which the background is defocused to the same extent while the moving targets are defocused differently. The indicator involved detects moving targets by comparing the sharpness of two defocused SAR images piece-by-piece, and then estimates the azimuth velocity of each detected target from its sharpness difference curve. The effectiveness of the optical architecture is investigated, and the proposal is confirmed by theoretical analysis and experiments with simulated and field data.

Radial velocity estimation of ground moving targets with a dual-frequency SAR

Radial velocity estimation is an important work in ground moving target indication using synthetic aperture radar, and we have designed a dual-frequency synthetic aperture radar (SAR) to perform this work. The estimation method is based on the estimate of the Doppler shift/centroid induced by the moving target without ambiguity using the two SAR images patch by patch which are generated by the transmitted pulses carried by the two frequencies. Furthermore, a method based on smear theory is used to extracted the moving target which have large azimuth but small radial velocity components, and by excluding the background the minimum detectable velocity becomes more small and the estimate becomes more accurate.

Ground moving target indication and parameters estimation using a dual-frequency synthetic aperture radar

A new scheme is presented to estimate the range and azimuth velocity components of a detected moving target by using a dual-frequency synthetic aperture radar (SAR). It consists of a moving target detector, a range velocity estimator, and an azimuth velocity estimator. In this scheme, two original SAR images are achieved from the returns first, and then processed by a symmetric defocusing filter pair (SDFP) to produce two defocused images. By comparing the sharpness of the two defocused images, the moving targets are indicated and isolated form each original SAR image. For a selected moving target, its range velocity component is estimated by using a Doppler ambiguity solver and a stepped approximation-and-comparison algorithm. After range velocity compensated, the target in the patch is concentrated in less range bins, and its azimuth velocity component is estimated by using an SDFP bank. Finally, the moving target is refocused and its azimuth displacement caused by range velocity component is corrected. The effectiveness of the proposed scheme is confirmed by the experiments with the field and simulated data.

Supper resolution radar imaging: A virtual array concept approach

A virtual array concept is proposed to get supper-resolution in synthetic aperture radar imagery. Two kinds of virtual arrays called virtual frequency array and virtual azimuth array are constructed, combining with phased array signal processing methods, to bring out better imaging performance than traditional range-Doppler and reciprocal spectrum algorithms used in previous literatures.

Reciprocal spectrum algorithm for radar imaging with frequency sampling waveform

A radar imaging algorithm named reciprocal spectrum algorithm (RSA) is proposed in this paper to get higher resolution in azimuth direction with frequency sampling waveform. Theoretical analysis and simulation results show that the algorithm can give better performance than the tradition range Doppler algorithm (RDA) at the cost of peak value reduction at the object points in radar image.