Fusion of Reference-Aided GPS, Imagery, and Inertial Information for Airborne Geolocation

摘要

A remote sensor suite is described that utilizes kinematic and differential GPS, a digital camera, and a tactical-grade Inertial Navigation System (INS). The camera and INS are fixed to a scan platform housed in a turret. The turret is attached to the chin of a light, single-engine aircraft. Real-time differential GPS positioning along with the real-time INS observations provide a pointing vector to a specific location on the ground, allowing the camera to continuously stare at that location as the aircraft flies by. Post-mission integration of the camera position and attitude, along with image information, can provide the ground locations of any point in the image in World Geodetic System (WGS-84) coordinates. Accurate geolocation of ground targets was demonstrated using data collected during a test conducted near Duck, North Carolina in October and November 1999. GPS pseudorange and phase measurements, as well as data from an inertial measurement unit (IMU), were collected in real-time; however, processing was done after the test. Absolute positions from the aircraft were obtained from either short- or long-baseline kinematic reference-aided GPS. Short-baseline kinematic GPS provided aircraft positions with centimeter-level accuracy, while multiple-reference, long- baseline, kinematic GPS (greater than 1000 km) provided decimeter-level accuracy. The use of these positions permitted more accurate IMU/camera attitude estimation than that achievable using standard differential GPS techniques. In particular, sub-milliradian standard errors for camera pointing accuracy were demonstrated. Target geolocation was performed using a two-image triangulation method. Meter-level target positioning errors were obtained for a circular aircraft trajectory with an average range-to-target of 2500 m. These target coordinates were verified by fusion with registered imagery.