For geometric correction, we need precise position and attitude knowledge of satellites. The ALOS has high precision star-trackers and an inertial reference unit for precision attitude determination, and a dual-frequency GPS receiver for precision position determination. In addition to onboard attitude and position determinations, off-line precision attitude and position determinations are provided to improve precision. The goal is to determine the position of each PRISM pixel on the ground to within 2.5 m.