Zero Doppler Steering Research Articles

Numerical Calculation of Doppler Steering Laws in Bi- and Multistatic SAR

This article defines Doppler steering laws for different bi- and multistatic acquisition geometries for synthetic aperture radar (SAR). Central swath line (CSL) and transmit swath line (TSL) acquisition geometries are introduced. Bistatic zero Doppler steering (BZDS) is defined. Multistatic acquisitions are classified into dedicated and supplementary types. Numerical approaches for the calculation of yaw, pitch, and roll angles are described providing zero Doppler, constant Doppler, and/or full Tx-Rx beam footprint overlap. The appendix provides an approximated analytical approach to calculate yaw and pitch angles to achieve a desired swath line.

Decentralized adaptive sliding mode control for beam synchronization of tethered InSAR system

Beam synchronization problem of tethered interferometric synthetic aperture radar (InSAR) is addressed in this paper. Two antennas of the system are carried by separate satellites connected through a tether to obtain a preferable baseline. A Total Zero Doppler Steering (TZDS) is implemented to mother-satellite to cancel the residual Doppler. Subsequently attitude reference trajectories for the two satellites are generated to achieve the beam synchronization and TZDS. Thereafter, a decentralized adaptive sliding mode control law is proposed to track these reference trajectories in the presence of model uncertainties and external disturbances. Finally, the stability of closed-loop system is proved by the corollary of Barbalat's Lemma. Simulation results show the proposed control law is effective to achieve beam synchronization of the system.

An Optimal Resolution Steering Method for Geosynchronous Orbit SAR

For satellites in geosynchronous orbit (GEO) using synthetic aperture radar (SAR), the direction of the satellite velocity vector in the Earth-centered, Earth-fixed (ECEF) coordinate system varies widely in one orbital period. When the velocity vector is approximately parallel to the range direction at equatorial latitudes, the 2-D sidelobes of the generalized ambiguity function (GAF) on the ground are non-orthogonal, which results in a significant deterioration in the ground resolution. To improve the ground resolution, this study investigates an optimal resolution steering (ORS) method for GEO SAR. The ORS method differs from the total zero Doppler steering (TZDS) method, which attempts to minimize the Doppler centroid. In the ORS method, a beam pointing direction is derived based on the constraints of optimal ground resolution. Then, a 2-D roll-pitch strategy is derived to obtain small steering angles, and the beam is steered to the optimal beam pointing direction. Finally, the ORS method is verified with simulations.

Research on Elliptic Orbit Total Zero Doppler Steering

星载合成孔径雷达(SAR)数据处理中，多普勒特性对于方位向性能以及成像精度都有直接的影响。基于轨道动力学理论，在椭圆轨道情况下，该文导出了同时考虑偏航控制和俯仰控制的多普勒中心频率解析表达式，分别分析了偏航控制和俯仰控制对多普勒中心的影响，提出一种基于椭圆轨道的全零多普勒方法，并用TerraSAR-X轨道参数进行了数值仿真，仿真结果表明，使用该方法后，多普勒中心频率被减小到不超过5 Hz，比传统的偏航导引方法缩小了约一百倍，比基于瞬时圆轨道的全零多普勒方法缩小了5倍，表明了该方法的有效性。

Total Zero Doppler Steering—A New Method for Minimizing the Doppler Centroid

This letter presents a new method, called total Zero Doppler steering, to perform yaw and pitch steering for spaceborne synthetic aperture radar (SAR) systems. The new method reduces the Doppler centroid to theoretically 0 Hz, independent of the range position of interest. Residual errors are only due to pointing inaccuracy or due to approximations in the implementation of the total zero Doppler steering law. This letter compares the new method with currently applied methods. The attitude angles and the residual Doppler centroid frequencies are calculated and depicted exemplarily for the parameters of TerraSAR-X, for which the new method will be implemented and used. The new method provides a number of advantages. The low residual Doppler centroid and the reduced variation of the Doppler centroid over range allow a more accurate Doppler centroid estimation. Due to the low residual Doppler centroid, the synthetic aperture radar (SAR) processing can be alleviated, since the range cell migration is reduced and the Doppler frequencies are low. This facilitates the use of very efficient processing algorithms, which are based on approximations whose quality is better for low Doppler frequencies. The new method will furthermore optimize the overlap of the azimuth spectra of SAR image pairs for cross-track interferometry. Low Doppler centroids will also reduce the impact of coregistration errors on the interferometric phase. Furthermore, scalloping corrections in the ScanSAR processing are alleviated due to the low variation of the Doppler centroid over range.