Analysis on the Performance Limitations of an Interferometric Geolocation Device

GPS is a critical tool often used in terrestrial location and navigation. However, GPS relies on a system of satellites in medium earth orbit and is prone to dropouts at higher latitudes, and may be susceptible to spoofing or other attacks. Thus, it is prudent to examine possible alternatives. Recently, star tracking has been of interest in global positioning. There are many implementations of a star tracker using an imaging-based optical system to capture star locations in order to estimate position using celestial navigation techniques. These imaging systems are performance limited by blurring imposed by atmospheric turbulence, platform jitter, and measurement noise. An interferometric system for locating stars can be used as an alternative to accurately locate stars in the sky. The use of one or more 3 or 4-aperture interferometers may allow for greater noise immunity in the phase error induced by atmospheric turbulence, and allows a larger baseline to be used as compared to the diameter of a single lens imaging system in some configurations. Such a system could sample at a rate higher than the Greenwood frequency, which helps reduce error in boresight angle retrieval. In the system described herein, the performance limitations would be dominated by atmospheric tilt and boresight angle retrieval. When the boresight angle can be retrieved, the system could be reasonably expected to produce a position estimate RMS error of less than 30 meters.