Quaternion-base direct geo-referencing algorithm for ISSAC

The International Space Station Agriculture Camera (ISSAC), Sponsored by the National Aeronautics and Space Administration´s (NASA) Education Office and developed by University of North Dakota, aims to demonstrate the applications of precision farming and natural resource management from the International Space Station (ISS). With a designed Ground Sampling Distance (GSP) of ~20 meters, an accurate geo-referencing algorithm is important for near-real time delivery of images that can be used immediately. One outstanding feature of ISSAC is its tilting capability in cross-track direction so that a wide area can be covered. At a relatively low altitude, the ISS, where the ISSAC will be hosted, experiences a large variation in attitude. Additionally, the optics window on ISS where the ISSAC sees through is not at the center of mass of the ISS. All these factors need to be taken care of in the algorithm. Evaluated by the commercial navigation software, Satellite Tool Kit (STK, Analytical Graphics, Inc.), the proposed algorithm can achieve theoretical accuracy within 0.5 meters.