The nonlinear characteristics of the motion trajectory of the synthetic aperture radar (SAR) flight platform can lead to severe two-dimensional space-variance characteristics of the signal, greatly affecting the imaging quality, and are currently considered as one of the difficulties in the field of SAR imaging. This paper first discusses the nonlinear trajectory SAR model and its space-variance characteristics and then discusses algorithms such as scaling-based algorithms, interpolation-based algorithms, time-domain algorithms, and hybrid algorithms. The relative merits and applicability of each algorithm are analyzed. Finally, computer simulation and actual data validation are conducted.

In order to mitigate speckle noise in synthetic aperture radar (SAR) images and enhance the accuracy of SAR tomography, non-local means (NL-means) filtering has been proven to be an effective method for improving the quality of SAR interferograms. Apart from considerations like noise type and the definition of similarity, the size and shape of filtering windows are critical factors influencing the efficacy of NL-means filtering, yet there has been limited research on this aspect. This paper introduces an enhanced NL-means filtering method based on adaptive windows, allowing for the automatic adjustment of filtering window size according to the amplitude information of the SAR interferogram. Simultaneously, a directional window is incorporated to align SAR interferograms, achieving the dual objective of preserving filtering standards and retaining detailed information. Experimental results on interferogram filtering and tomography, based on TerraSAR-X data, demonstrate that the proposed method effectively reduces phase noise while maintaining texture accuracy, thereby improving tomography quality.

Synthetic aperture radar (SAR) is able to acquire high-resolution method using the active microwave imaging method. SAR images are widely used in target recognition, classification, and surface analysis, with extracted features. Attribute scattering center (ASC) is able to describe the image features for these tasks. However, sidelobe effects reduce the accuracy and reliability of the estimated ASC model parameters. This paper incorporates the SAR super-resolution into the ASC extraction to improve its performance. Both filter bank and subspace methods are demonstrated for preprocessing to supress the sidelobe. Based on the preprocessed data, a reinforcement based ASC method is used to get the parameters. The experimental results show that the super-resolution method can reduce noise and suppress sidelobe effect, which improve accuracy of the estimated ASC model parameters.

Multichannel high-resolution and wide-swath (HRWS) imaging is an advanced digital beamforming technique for future synthetic aperture radar (SAR) systems. However, radio frequency interference (RFI) is a critical concern for HRWS SAR missions, which distorts measurements and produces image artifacts. In this paper, the spatial cross-correlation coefficients of multichannel HRWS SAR signals are investigated for RFI detection. It is found when the two channels are correlated, RFI-polluted areas present lower coherence values than non-polluted areas in the same scenarios, which makes previous methods fail. Further, this paper studies the case of two fully decorrelated channels to maximize the coherence difference among RFI and target echoes, and RFI detection is realized by exploiting the anomaly value of coherence. Experimental results of real airborne multichannel SAR data demonstrate that the RFI can be detected successfully.

Multi-temporal synthetic aperture radar interferometry (MT-InSAR) is a standard technique for mapping clustering and wide-scale deformation. A linear model is often used in phase unwrapping to overcome the underdetermination. It’s difficult to identify different types of nonlinear deformation. However, the interpretation of nonlinear deformation is very important in monitoring potential risk. This paper introduces a comprehensive approach for identifying and interpreting different types of deformation within InSAR datasets, integrating initial clustering and classification simplification. Initial classification is performed using the K-means clustering method to cluster the collected InSAR deformation time-series data. Then we use F test and Anderson-Darling test (AD test) to simplify the clusters after initial classification. This technique distinctly discerns the changing trends of deformation signals, thereby providing robust support for interpreting potential deformation scenarios within observed InSAR regions.

Synthetic aperture radar (SAR) three-dimensional (3D) imaging technology can reconstruct the complete structure of observed targets and has been a hot topic. Compared with tomographic SAR, array interferometric SAR, and circular SAR, curve SAR can use less data to achieve 3D positioning of targets. Most existing algorithms for estimating Doppler frequency modulation (FM) rate are based on sub aperture partitioning, resulting in low computational efficiency. To address this, this article establishes a target height estimation model, which reflects the relationship between the height and the residual Doppler FM rate for spaceborne curve SAR. Then, a fast SAR 3D localization processing flow based on fractional Fourier transform (FrFT) is proposed. Experimental verification demonstrates that this method can estimate the Doppler FM of the target column by column, and the 3D position error for non-overlapping targets is controlled within 1 m. For overlapping points with an intensity ratio greater than 1.5, the root mean square error (RMSE) of the estimation results is around 5 m. If the separation between overlapping points is greater than 35 m, the RMSE decreases to approximately 2 m.

The near-Earth asteroid collisions could cause catastrophic disasters to humanity and the Earth, so it is crucial to monitor asteroids. Ground-based synthetic aperture radar (SAR) is an observation technique for high resolution imaging of asteroids. The ground-based SAR requires a long integration time to achieve a large synthetic aperture, and the echo signal will be seriously affected by temporal-spatial variant troposphere. Traditional spatiotemporal freezing tropospheric models are ineffective. To cope with this, this paper models and analyses the impacts of temporal-spatial variant troposphere on ground-based SAR imaging of asteroids. For the background troposphere, a temporal-spatial variant ray tracing method is proposed to trace the 4D (3D spatial + temporal) refractive index network provided by the numerical weather model, and calculate the error of the background troposphere. For the tropospheric turbulence, the Andrew power spectral model is used in conjunction with multiphase screen theory, and varying errors are obtained by tracking the changing position of the pierce point on the phase screen. Through simulation, the impact of temporal-spatial variant tropospheric errors on image quality is analyzed, and the simulation results show that the X-band echo signal is seriously affected by the troposphere and the echo signal must be compensated.

Mainly for the problems that the configuration of the mobile cable on the satellite is very easy to change, the motion trajectory and dynamic characteristics of the cable can not be accurately predicted, which affects the laying quality seriously, the dynamic modeling and simulation of mobile cable on the satellite are carried out. On the basis of referring to the previous papers, the existing mathematical model is improved. The equations of the base vector of the cable section principal axis coordinate system with respect to the arc coordinate s, the distribution force of cable balance equation, the matrix expression of the base vector after the rotation motion transformation in the section principal axis coordinate system, the angular velocity of cable, the section elastic strain and velocity calculation equations are given, and the Cosserat dynamic modeling of the mobile cable is established. Finally, the dynamic simulation model of the mobile cable assembly of the kinematic mechanism is established, and the changes of the force and torque on the cable constraint end are obtained, which provides a reference for the dynamic modeling and simulation of the mobile cable on satellite.

Mainly for the problem that the friction force generated by the existing process of binding, fixing and fastening the flexible cable on the satellite is unknown, the friction force analysis and experimental research on the binding point of the flexible cable are carried out. The equivalent model of the cable bundle bound by nylon cable ties is established, the force on the binding point is analyzed, and the empirical formula for calculating the friction force at the binding point is established. The formula shows that the friction force is related to the cable bundle diameter, the number of winding cycles of silicone rubber tape, the width of nylon cable ties, and the binding force. The friction force tests of the cable diameter of 5.06 mm, 8.02 mm, 24.02 mm, 38.04 mm under different winding turns of tape were carried out, which was compared with the theoretical calculation value. It is concluded that the calculation accuracy of the theoretical model is more than 95%, which can estimate the actual friction force value accurately. This provides a reference and basis for the theoretical and experimental research on the friction force of the flexible cable binding point on satellite.