High altitude terrain correlation navigation resetting by nadir looking synthetic aperture radar

Terrain correlation for navigation resetting is an operational technique for nap-the-earth to low altitude cruise missiles since the 80's. It allows these systems to perform their mission even when Global Navigation Satellite System (GNSS) or ground based radio-navigation beacons are damaged, compromised or jammed. Direct transposition to high altitude is however impractical because an high altitude radio altimeter would require both accurate nadir steering and very narrow beam (hence a very large antenna and/or high frequency band) to illuminate a small enough area below the aircraft. Both beam narrowing and nadir steering can be performed by synthetic aperture in the along-track direction thus allowing high altitude operation. And experiments show that the wide beam width and the absence of resolution in the across-track direction have no negative impact on the accuracy of the position resetting. Bistatic (i.e., illumination from a different platform) version of the algorithm is evaluated for transposition in the acoustic domain (navigation resetting for submarines from bathymetry correlation).