Very High Resolution SAR Imaging With DGPS-Supported Airborne X-Band Data

High spatial resolution imaging in synthetic-aperture radar (SAR) can provide accurate monitoring capacity and has been gaining great attention recently in the fields of military and civilian. Apparently, the slant range resolution of the SAR system depends on the radar operating bandwidth. Currently, the large bandwidth signal synthesizing technology of the stepped frequency chirp signal waveform is highly practical for achieving high spatial resolution. However, the system structure and the corresponding signal processing technology become more complex. In order to verify the feasibility and operability of the large full-bandwidth system, a 3.6-GHz full-bandwidth airborne experimental SAR system operating at X-band, featured by full-bandwidth transmitting and receiving, has been designed by the Department of Space Microwave Remote Sensing System, Institute of Electronics, Chinese Academy of Sciences, as a test bed for the development and implementation of the future spaceborne realizations. For this large full-bandwidth SAR system, in addition to the hardware resource, the motion compensation (MOCO) is an urgent problem. The improvement of spatial resolution will aggravate the effect of motion errors. In order to focus the SAR images accurately, this article presents a technical approach by utilizing the differential global positioning system (DGPS) technology to improve the position accuracy of the inertial measurement unit device. Meanwhile, considering the significant deviation of range cell migration correction (RCMC) due to the residual range-variant errors, this article proposes an accurate MOCO strategy with DGPS-supported to implement the second-order MOCO, space-variant residual range envelope, and space-variant residual phase error in azimuth before RCMC. Finally, this article presents the outfield experiment and reports the corresponding analysis and processing results of an outfield flight experiment successfully conducted in March 2019.