Analysis of Steering Approach for High Resolution Spaceborne Synthetic Aperture Radar with Large Scanning Angle In highresolution spaceborne Synthetic Aperture Radar (SAR) system design, spotlight and sliding spotlight imaging mode are generally applied. As the increasing resolution and swath length in azimuth, the required scan angle of the antenna pattern become larger. However, due to curved orbits of satellites, the scan speeds and the steering angles are spatial variable. In this condition, the traditional steering method with one dimensional uniform scannning speed is inadequate. Therefore, in this paper, the two dimensional scanning regulation of steering angle of antenna pattern is analyzed in detail. All the analysis and simulation results demonstrate the particularities and show the required twodimensional nonlinear scanning angles for highresolution spaceborne SAR system.

Feasibility of Replacing the Range Doppler Equation of Spaceborne Synthetic Aperture Radar Considering Atmospheric Propagation Delay with a Rational Polynomial Coefficient Model Usually, the rational polynomial coefficient (RPC) model of spaceborne synthetic aperture radar (SAR) is fitted by the original range Doppler (RD) model. However, the radar signal is affected by twoway atmospheric delay, which causes measurement error in the slant range term of the RD model. In this paper, two atmospheric delay correction methods are proposed for use in terrainindependent RPC fitting: singlescene SAR imaging with a unique atmospheric delay correction parameter (plan 1) and singlescene SAR imaging with spatially varying atmospheric delay correction parameters (plan 2). The feasibility of the two methods was verified by conducting fitting experiments and geometric positioning accuracy verification of the RPC model. The experiments for the GF3 satellite were performed by using global meteorological data, a global digital elevation model, and ground control data from several regions in China. The experimental results show that it is feasible to use plan 1 or plan 2 to correct the atmospheric delay error, no matter whether in plain, mountainous, or plateau areas. Moreover, the geometric positioning accuracy of the RPC model after correcting the atmospheric delay was improved to better than 3 m. This is of great significance for the efficient and highprecision geometric processing of spaceborne SAR images.