SAR and Orthophoto Image Registration With Simultaneous SAR-Based Altitude Measurement for Airborne Navigation Systems

This article addresses two substantial issues connected with using synthetic aperture radar (SAR) imaging to improve the robustness of airborne navigation systems for global positioning system (GPS) signal jamming. The first is related to the problem of automatic trajectory correction estimation based on image registration. The authors propose a method dedicated to SAR systems called cumulative minimum square distance matching (CMSDM). It allows for real-time trajectory error estimation of the inertial navigation system (INS) and, as a result, enables correction estimation when the global navigation satellite system (GNSS) signal is unavailable or jammed. The intense simulation study and real-life data processing show the essential improvement and acceleration of processing compared to the state-of-the-art technique. For the correct operation of the navigation system based on the CMSDM algorithm, precise knowledge of the altitude of the airborne platform is necessary. With a jammed GNSS signal, this may not be achievable with traditional methods. Thus, the second issue discussed in this article is the estimation of the airborne platform’s altitude with the use of SAR images. Also, in this case, the experiment has shown that the proposed solution works correctly and can be a precious source of navigational data.