To realize real-time imaging for the spaceborne synthetic aperture radar (SAR) using the chirp scaling (CS) algorithm, high generation rates of phase factors and heavy computation loads are unavoidable. For example, updating phase factors continuously in the 2-D time or frequency space is difficult for generating phase factors for real-time imaging. To solve this problem, a modified CS algorithm based on updating phase factors regionally is proposed. Moreover, conventional floating-point arithmetic is unaffordable for real-time imaging onboard. Therefore, fixed-point processing is adopted. In the proposed imaging algorithm, the phase factors are updated only at some specified times and frequencies, and fixed-point operation is adopted. Furthermore, based on the paired echo theory and the finite word length error mathematical model, the effect of the proposed imaging algorithm on the SAR image quality is studied. Moreover, based on the above analysis and the experiments of Chinese HJ-1C and GF-3 spaceborne SAR practical measured data, a hardware system including digital signal processor and field-programmable gate array boards is constructed.

Dual-channel synthetic aperture radar (SAR) system is promising in high-resolution wide-swath (HRWS) imaging. However, gain and phase unbalance in the dual-channel SAR system will severely degrade the performance. To make clear the channel error effect on the image of the reconstruction algorithm, a precise analysis of the channel error effect is proposed in this letter. Based on the channel error effect analysis, the amplitude and position of the ambiguity caused by the channel error can be calculated, which is significant for understanding the image quality degradation caused by channel unbalance. Finally, based on the Chinese first dual-channel spaceborne SAR system--GF-3, the validity of this letter is verified by the simulated and real data, respectively.

Yaw steering is an important technique for bistatic spaceborne synthetic aperture radar (SAR), traditionally implemented separately at the master and slave satellites, such as the X-band TerraSAR-X/TanDEM-X system. This separate yaw steering method, however, will degrade the illumination synchronization between the master and slave satellites. With the increment in frequency band and master–slave distance, the degradation will get worse, leading to intolerable azimuth resolution degradation or even failure of imaging. To solve this problem, a new joint yaw steering (JYS) method is proposed for bistatic spaceborne SAR with an arbitrary configuration in this letter. The word “joint” means that the master and slave satellites cooperatively work to always make their beams point to an identical point on the Earth’s surface. In this way, the best illumination synchronization can be achieved, contributing to the best available azimuth resolution. The presented approach has been evaluated through computer simulations.

Differential SAR interferometry (DInSAR) is a useful technique used to measure small movements and surface deformation. However, ionospheric phase screens are a major error source in multipass terrain observation by progressive scans sar (TOPSAR) interferograms. In this letter, an improved split-spectrum method is proposed. First, the burst used for ionospheric phase estimation is selected through coherence, and then, the ionospheric phase of the burst is estimated based on the split-spectrum method. Finally, the TOPSAR ionospheric space-variable phase in a large scene is obtained through 2-D space-variable fitting, which avoids the complicated processing of splicing between bursts of different periods and reduces the number of unwrapping calculations for large scenes after splicing. The method can ensure that the number of calculations is reduced without loss of accuracy. Sentinel-1 TOPSAR real data processing verifies the correctness of the proposed method.