The coherence level and number of selected interferometric pairs are directly related to the interferometric synthetic aperture radar (InSAR) phase estimation accuracy. In the Multi-Channel InSAR and Multi-Temporal InSAR, it is essential to select high-coherence interferometric pairs and remove low-coherence ones from the massive SAR singlelook complex (SLC) image data. The existing selection method, which based on basic coherence spectral clustering, may become increasingly computationally intensive when processing real-time data. To make a trade-off between the calculation cost and selection accuracy, a novel SAR interferometric pairs selection method based on incremental coherence spectral clustering is proposed. Experimental results demonstrate that the proposed method, which involves selecting a representative SAR SLC image for each cluster rather than re-constructing the adjacency matrix and re-estimating the number of clusters, can yield similar interferometric pairs selection results at a reduced computational cost.

The strong sea clutter and noise in synthetic aperture radar (SAR) images will cover weak ship wakes, making it difficult for conventional ship wake detection methods to accurately detect ship wakes. A ship wake detection method based on joint sparse representation is proposed in this paper to improve the detection effect of ship wakes in complex backgrounds. Firstly, the sparse representation model of SAR images based on the Radon transform is constructed. Secondly, using dual-domain images in the spatial and gradient domains, the optimization function for ship wake detection based on joint sparse representation is constructed and solved iteratively. Then, the weighted clustering criterion based on sparse coefficient and Radon coordinates is used to perform sparse coefficient clustering, and the centerline detection of the ship wake is realized by the inverse Radon transformation of the cluster center. Finally, the experimental results of TerraSAR-X images are used to verify the effectiveness of the proposed method.

The carrier frequency and bandwidth are vital parameters of radar transmit signals. In this article, a joint design of frequency and bandwidth in multifrequency synthetic aperture radar (SAR) is proposed to improve the target information acquisition capability. First, the target detection mutual information (MI) is considered as the performance metric, and its mathematical expression is derived using the example of decision-level fusion and hypothesis testing. The design is formulated as an optimization problem with multiple engineering constraints based on MI maximization. Then, a modified genetic algorithm (GA) is proposed to find the optimal solution satisfying the constraints via a code adjustment operator. It is shown by simulation results that for a specific scene, the multifrequency SAR with its frequencies and bandwidths designed by the proposed method has higher target information acquisition capability and more accurate target detection performance than existing spaceborne SAR systems.

Aiming at the problem of insufficient target information acquisition caused by the experience of frequencies selection in the existing multiband SAR system, the optimal frequencies design method of multi-frequency SAR under the maximum mutual information criterion (MMIC) is proposed. After constructing the multi-frequency SAR information acquisition system model, the frequencies design objective function of discrete signal under MMIC is derived. With the limit of engineering practice—frequencies number, range and interval, the constrained optimization problem is constructed, and the optimal frequencies is solved by genetic algorithm. Simulation experiments for specific target verify the effectiveness of the proposed frequencies design method.

Synthetic aperture radar tomography (TomoSAR) at different radar wavelength can be used to measure different structural elements of forests. In this letter, we compared the airborne P- and L-band synthetic aperture radar (SAR) tomograms and TomoSAR-measured canopy height model (CHM) and above-ground biomass (AGB) over a tropical forest in Lopé, Gabon. The SAR data sets were acquired by German Aerospace Center (DLR)’s F-SAR system during the AfriSAR2016 campaign. First, the Weighted covariance fitting-based Iterative Spectral Estimator (WISE) was applied to obtain tomograms. CHM was then retrieved based on the canopy phase center derived from the tomograms. Finally, AGB was estimated via an empirical logarithmic model developed from field measurements and the tomographic backscatter power of vegetation layers between 40 and 50 m above ground. Compared with the classical approaches of Capon and Wavelet-based Compressed Sensing, the WISE method can achieve better resolution with higher computational efficiency and reduce the ambiguity level of L-band tomograms successfully. The experimental results also show that there is no substantial difference between P- and L-band TomoCHM, while P-band tomographic intensity is more sensitive than the L-band for the inversion of tropical forest AGB at a resolution of 50 m$\times $50 m.

The spatial localization of interference source is a critical procedure in Radio frequency interference (RFI) suppression. It is not suitable to use traditional multi-station interference localization methods in most synthetic aperture radar (SAR) systems. This paper proposes a novel method of single RFI localization based on conjugate cross-correlation of dual-channel SAR signals. First, interference detection technology is applied to check whether echo signal is interfered. Then, conjugate cross-correlation is performed on SAR signals, and the distance difference between interference source and receiving channels is calculated. Finally, spatial localization equations of interference source are established, and optimization algorithm is applied to solve the coordinates of interference source. The results of simulation experiments illustrate the effectiveness of the proposed method.

Recently, electromagnetic (EM) vortex with orbital angular momentum (OAM) attracts more attention in radar imaging fields, which needs a variety of OAM modes. However, most of them are based on motion relative static. In this paper, we propose a novel SAR imaging method based on electromagnetic vortex with OAM. The geometry model of synthetic aperture radar (SAR) is utilized for EM vortex with OAM and the echo signal model is deduced correspondingly, including the additional phase items produced by EM vortex waves. Then the imaging algorithm aiming at OAM based on Chirp-Scaling algorithm is proposed. Simulation results validate the effectiveness of the proposed method and that OAM beams can be applied in SAR signal processing.

Spaceborne D-InSAR system is a kind of SAR satellite system aiming at differential interferometry application. It provides us a capability of measuring subtle deformation on the ground with phase difference. In this work, we focused on the system performance analysis theory as a first step to launch the research work on the overall spaceborne D-InSAR system. After the theoretical model and major error analysis work, we realized that coherence is really important. The qualitative and quantitative analysis showed that the situation becomes worse due to volumetric and temporal decorrelations compared with single-pass InSAR system such as TanDEM-X system. The in-orbit SAR satellite data experiment study validated the quantitative analysis. In order to obtain high-precision D-InSAR measurement, there are some new problems to solve rather than just using an existing SAR satellite to implement D-InSAR.

Attitude stability is a very important design parameter to synthetic aperture radar (SAR) satellite platform. The mathematical expression of distributed satellite SAR system impulse response function with attitude jitter is studied using paired echo theory. The effect of attitude stability on interferometric performance is confirmed according to the change of peak sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR). The constraint relationship is given between three-axis attitude jitter and interferometric performance. Through computer simulation, the relationship curve is obtained to verify the conclusion. The study in this paper provides an important theoretical basis for the integrated design of distributed satellite SAR system.