Abstract
For accurate motion compensation (MOCO) in airborne synthetic aperture radar (SAR) imaging, a high-precision inertial navigation system (INS) is required. However, an INS is not always precise enough or is sometimes not even included in airborne SAR systems. In this paper, a new, raw, data-based range-invariant motion compensation approach, which can effectively extract the displacements in the line-of-sight (LOS) direction, is proposed for high-resolution sliding spotlight SAR mode. In this approach, the sub-aperture radial accelerations of the airborne platform are estimated via a well-developed weighted total least square (WTLS) method considering the time-varying beam direction. The effectiveness of the proposed approach is validated by two airborne sliding spotlight C band SAR raw datasets containing different types of terrain, with a high spatial resolution of about 0.15 m in azimuth.
Highlights
SLIDING spotlight synthetic aperture radar (SAR) is designed to provide a compromise between spotlight and stripmap modes, where the rotation center of the antenna beam is located beyond the beam footprints, increasing the observed azimuth scene extension at the expense of azimuth resolution [1,2]
To demonstrate the performance of the proposed approach, sliding spotlight mode raw echo data collected by an experimental airborne radar, which was developed by the Institute of Electronics, data collected by an experimental airborne radar, which was developed by the Institute of Electronics, Chinese Academy of Sciences, is processed
Note that the sliding spotlight mode spotlight mode in the experimental system is originally designed with broadside geometry, the small in the experimental system is originally designed with broadside geometry, the small squint angle squint angle presented in Table 1 is mainly caused by the yaw motion of the airborne platform
Summary
SLIDING spotlight synthetic aperture radar (SAR) is designed to provide a compromise between spotlight and stripmap modes, where the rotation center of the antenna beam is located beyond the beam footprints, increasing the observed azimuth scene extension at the expense of azimuth resolution [1,2]. The first problem is that the total Doppler bandwidth is generally greater than the pulse repetition frequency (PRF), especially for the spaceborne case, due to the azimuth beam steering in the sliding spotlight mode [1,2] To solve this problem, several efficient algorithms have been developed for sliding spotlight SAR data processing [3,4,5,6,7,8] such as the extended chirp scaling (ECS) algorithm [3], baseband azimuth scaling algorithm [4] and the two-step processing algorithm as well as its improvements [5,6,7,8], most of which are based on the conventional stripmap imaging algorithms. In many cases, an INS is not included or not precise enough in the SAR system due to the limit of the airborne platform, such as light weight aircrafts and unmanned aerial vehicles (UAV) Under this condition, raw data-based first-order MOCO techniques need to be developed to replace the function of INS, which motivates the development of the method proposed in this paper.
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