Existing false moving target generation methods face challenges such as uncontrollable position and velocity when against multichannel synthetic aperture radar ground moving target indication (SAR-GMTI) system, as well as significant computational burden in generating dense false targets. Meanwhile, current false blocking image generation methods struggle to create blocking images with controllable position and coverage shape, and the generated images will be partially cancelled against multichannel SAR-GMTI. To tackle these issues, we propose a smart multi-transmitter cooperative false images generation method against multichannel SAR-GMTI and present an accurate and a fast implementation scheme of the method in this paper. The accurate implementation scheme is referred to as the multi-transmitter cooperative frequency-shifting modulation jamming (MTC-FSMJ) method, which can generate false moving targets with controllable radial velocities and initial positions by utilizing multiple transmitters. However, due to the need for iteration calculations in generating a single false target, the computation load of the MTC-FSMJ method becomes substantial when generating dense false moving targets. When we want to generate dense false moving targets, a fast implementation scheme known as the multi-transmitter cooperative template-modulated jamming (MTC-TMJ) method provides an excellent alternative. This approach can quickly generate dense false moving targets within the template without iteration calculations. Moreover, by reasonably designing the template, the MTC-TMJ method can also generate false blocking images with controllable positions, while avoiding partial cancellation. Theoretical analysis and simulation experiments have verified the effectiveness of both implementation structures.

A sparse planar array often suffers from the strong grating-lobes that deteriorate inversion performance due to spatial undersampling. In the paper, a diffraction tomography (DT) algorithm is proposed to solve three-dimensional (3-D) electromagnetic inverse scattering problems with a sparse planar array and polarization diversity. The method deals with multifrequency multipolarization data as follows: firstly, doing a polarization fusion; next, using the exact coordinate transformation; then decoupling and modifying the aliased multifrequency spatial spectrum of the permittivity and the conductivity; finally, applying the range-normalization two-dimensional coherence factor (2-D CF) weighting. The weak scatterers’ geometries and dielectric properties can be well reconstructed under low-contrast conditions, and the non-weak scatterers can also be detected. The proposed method outperforms the conventional DT approach regarding grating-lobes and noise suppression without compromising quantitative inversion performance, as demonstrated by the inverted results obtained from synthetic and experimental data.

Existing frequency-diverse array (FDA)-based jamming methods against synthetic aperture radar (SAR) still require complex modulation calculations to generate false area targets as the traditional SAR jamming method does, and cannot generate them solely without the regular distribution or repetition in range in SAR images. However, such regular distribution or repetition tends to make false area targets easily identifiable. Therefore, in order to create flexible jamming both in range and azimuth, this letter first proposes a method to obtain Doppler-modulation phase using the Fast Fourier transform (FFT) of a template along the azimuthal direction, which can help the jammer generate template-based jamming in the azimuth domain. Then, by leveraging the distinctive features of FDA’s multifrequency transmission structure, which allows for accurate determination of range positions of false targets within the template, and incorporating the utilization of Doppler-modulation phase, a template-modulation jamming method based on the FDA is proposed. This method can produce solely two-dimensional template-based deceptive or controllable suppression jamming in SAR images without complex modulation calculation requirements. As the final jamming result is determined by the template constructed, the regular jamming distribution can be avoided. The effectiveness of the proposed method is validated through theoretical analysis and simulation experiments.

Without phase information of the measured field data, the design complexity of the observation equipment can be greatly simplified. In the meantime, the phaseless data inverse scattering problems counter more serious nonlinearity and ill-posedness compared to the full data ones. In this article, a multifrequency cross-correlated contrast source inversion (CSI) method using phaseless measurements of the total fields (referred to as PD-CC-CSI) is proposed. By introducing the cross-correlated error term to the cost functional, PD-CC-CSI shows better robustness against data noise and challenges in more complicated inversion scenarios. Inverted results with transversal magnetic (TM) polarized synthetic and experimental data demonstrate the advantages of PD-CC-CSI in comparison to the phaseless data CSI (PD-CSI) method and its variant PD-MR-CSI. In addition, an empirical approach has been proposed to effectively determine the optimal inverted results. Since a fast algorithm can be straightforwardly applied, phaseless inversion with multifrequency data can be done within a few minutes.

Diffraction tomography (DT) is a linear approach to solving electromagnetic inverse scattering problems. Based on the weak scattering assumptions (such as Born or Rytov approximations), the spatial spectrum of the contrast at one certain frequency is a linear mapping of the scattered field data. As is well known, using more frequencies means better performance of noise suppression. However, the spatial spectra are aliased in cases of multi-frequency data. In addition, the permittivity and the conductivity are coupled in the aliased multi-frequency spatial spectrum. In this paper, a quantitative DT for weak scatterers is proposed by firstly doing a coordinate transformation, then decoupling the permittivity and the conductivity, and finally modifying the aliased multi-frequency spatial spectrum. In doing so, the modified spatial spectra of the permittivity and conductivity are formulated respectively, leading to a quantitative diffraction tomography for weak scatterers based on aliasing modification of the multi-frequency spectrum. Inversion results with synthetic and experimental data demonstrate that the proposed method outperforms the conventional DT approach in terms of quantitative inversion accuracy for weak scatterers of multi-frequency data while maintaining the anti-noise performance.

For the special azimuth multichannel reconstruction processing of high-resolution wide-swath single-input multiple-output synthetic aperture radar (HRWS-SIMO-SAR) to resolve the Doppler ambiguities, this letter studies the imaging characteristics of conventional SAR Doppler-modulation jamming (DMJAM) in HRWS-SIMO-SAR to provide the theoretical basis for the development of HRWS-SIMO-SAR anti-jamming technology. The theoretical analysis points out that the DMJAM signal will generate equally spaced false targets along the azimuth direction after imaging, and the amplitude of the false targets is decided by the combined sinusoidal function and matched filter loss associated with the Doppler-modulation frequency. The simulation experiments verify the accuracy of the theoretical analysis.

In polarimetric synthetic aperture radar (PolSAR) images, strong scattering centers on man-made targets contaminate their adjacent weak scattering points. We can use the target null theory to mitigate this effect, so that we can acquire the adequate scattering mechanism of these weak points. Since the efficiency of the theory depends on the system biases of the transmitting/receiving polarimetric channels, we analyze the relationship between suppression efficiency and the system bias requirement when the PolSAR system works in two modes: the alternate transmit and simultaneous receive (ATSR) mode and the simultaneous transmit and simultaneous receive (STSR) mode. The theoretical model proposed in this letter is verified by electromagnetic simulations and GF-3 data.

For current polarimetric system, the antenna usually transmits and receives electromagnetic waves with H and V polarizations which benefits the analysis and recognition of distributed targets greatly. However, for manmade target detection, the weak scattering mechanisms which characterize the structure of the target cannot be extracted with the fixed polarization. Aiming at this problem, the method proposed in this paper can be applied to suppress the strong scattering components based on target null theory. In the numerical simulation, the weak scattering mechanisms can be extracted correctly with the analysis of Cameron decomposition.

Roll-invariant polarimetric features which are independent of target orientation angle along the radar line of sight are popularly adopted in many radar application fields. During the development history of radar polarimetry, a number of roll-invariant polarimetric features have been reported in terms of different polarimetric matrix formulations, different target decomposition approaches and different scattering mechanism interpretation tools. Currently, there is lack of a comprehensive summary of these valuable roll-invariant polarimetric features. Also, their inner-relationships need to be further disclosed. Finally, deep investigations of their application potentials are essentially necessary. This work is dedicated to these aforementioned issues and a survey of roll-invariant polarimetric features is carried out.

In synthetic aperture radar (SAR) images, scattering centers (SCs) from the same geometric structure of the man-made target usually have the same scattering type and similar coordinates. Inspired by this observation, a novel clustering-based geometrical structure retrieval (C-GSR) method is proposed to estimate the geometrical structure of targets by clustering SCs according to their types and coordinates. The C-GSR method considers each peak in a SAR image as a single SC and extracts both frequency and polarization features for classification. Then, SCs are efficiently clustered using the density-distance-based clustering algorithm. Finally, the geometrical structure corresponding to each canonical scatterer can be retrieved by computing the coordinates of SCs associated with the corresponding cluster. Experimental results have demonstrated the feasibility and accuracy of the proposed C-GSR method.

As having the imaging ability of area in front of flight direction, forward-looking synthetic aperture radar (SAR) has become a hot topic in areas of SAR research. Nevertheless, the currently exploited imaging algorithms of forward-looking SAR suffer from poor azimuth resolution induced by limited azimuth aperture length. To address this challenge, we develop a super-resolving imaging algorithm for forward-looking SAR based on compressive sensing theory. Firstly, the spatial geometry and signal model of forward-looking SAR is analyzed. After that, the compressive sensing theory is introduced to improve azimuth resolution. Imaging simulations based on Ku-band image data from the MiniSAR system demonstrate the effectiveness of the proposed method.

This paper presents the development of a uniform polarimetric matrix rotation theory in the rotation domain along the radar line of sight for polarimetric SAR (PolSAR) data interpretation. The uniform representation of each coherency matrix element is a sinusoidal function in the rotation domain. A set of oscillation parameters, including oscillation amplitude, oscillation center, angular frequency and initial angle, is proposed to fully characterize the scattering behavior in the rotation domain. A set of rotation angle parameters, including stationary angle, null angle, and minimization/maximization angles, is derived from the angular frequency and initial angle to indicate the specific states of the rotation property. A look-up table for these parameters is provided and their physical meanings are interpreted. The proposed theory generalizes both the classic polarization orientation (PO) angle originally derived from the covariance matrix in a circular polarization basis and the deorientation theory developed from the minimization of the cross-polarization term. The roll-invariant terms have also been summarized. Finally, multi-frequency AIRSAR and Pi-SAR PolSAR data sets are used to demonstrate the derived parameters.

The growing interest in 3-D reconstruction of targets, particularly man-made objects, has made synthetic aperture radar (SAR) tomography a hot topic in recent years. It obtains a 3-D reflectivity map by coherently processing multiple images acquired from slightly different views. This paper investigates the use of polarimetric tomographic SAR to reconstruct 3-D images of man-made objects and proposes a polarimetric 3-D reconstruction technique, based on the multiple-measurement vector compressive sensing (CS) (MMV-CS) model and Tikhonov regularization theory. The main feature of the technique is that of allowing joint reconstruction of polarimetric 3-D reflectivity maps with high resolution. For X-band tomographic SAR, we demonstrate that the phase error induced by an array element error is severe enough to prevent data focusing and propose a phase calibration technique employing prominent scatterers to adapt the proposed technique to practice. To check the plausibility of our algorithms, a ground-based SAR system is introduced, and high-resolution 3-D images obtained by processing the real collected data are presented. As special cases of the new proposed technique, both the Tikhonov regularization and the MMV-CS method reconstruct the targets successfully and give an accurate estimate for the vehicle size. Compared to the Tikhonov regularization method, the MMV-CS technique exhibits much better superresolution power and lower sidelobe level. The advantage of the MMV-CS technique over the single-measurement vector CS technique is also demonstrated, and the phase calibration algorithm is verified.

A new polarimetric tomography technique based on compressive sensing is proposed in this paper for the applications such as 3D reconstruction of man made target. Compared to the existing methods, the advantages of this new technique are those of preserving full image resolution, no model order selection procedure, high resolution, and low sidelobe artifacts. The effectiveness of the technique is demonstrated by processing real data collected by ground rail SAR.

This paper is comment on “Orientation Angle Preserving A Posteriori Polarimetric SAR Calibration”.

The various applications of polarimetric SAR data have brought to the fore questions of polarimetric calibration. Most polarimetric calibration methods based on distributed targets employed reflection symmetry assumption, which might be inconsistent with the truth due to a possible orientation angle shift, and therefore would skew the polarimetric signatures of targets. In this paper, a model incorporating orientation angle shift effect is introduced to characterize the POL SAR data, and a numeric algorithm is presented. The proposed calibration method can preserve the orientation angle information precisely. Simulations and real SAR data experiments are performed to test the proposed method.