부산대학교 도서관

Precise point positioning (PPP) with the international GNSS service (IGS) products, which consist of precise orbits and clock correction information, has been demonstrated by several investigators to achieve a centimeter-decimeter level positioning accuracy in real-time for land and aerial vehicular navigation. The purpose of this paper is to present one phase of study conducted at National Defense Academy (NDA) on performance evaluation when such a PPP technique is extended for orbit determination of the low Earth orbiters (LEO) in post-flight processing or even in real-time. In the present study the satellite CHAMP was selected as an LEO since high accuracy orbit is prerequisite to that mission. A PPP filter with a simple white noise plant model was designed, and a basic PPP software which was originally developed at NDA for land and aerial vehicles was intensively modified to process GPS data taken by the dual-frequency receiver “BlackJack” onboard the CHAMP satellite. To generate a reference orbit of CHAMP, we proposed a hybrid orbit determination (OD) method consisting of classical least-squares and Hill-Clohessy-Wildshire (HCW) solution, where a least-squares point positioning solution of 3-D coordinates from pseudoranges of CHAMP was employed as the pseudo-observations. It was shown that our PPP filter produced an overall positioning accuracy of better than a sub-meter for transverse and normal components and 90 cm for radial component for 3-hour data arc, and in particular of a few decimeters for each component over the last one-hour segment of good-quality data (no data gap), the implication of the precision real-time on-orbit satellite navigation using only a single, dual-frequency GPS receiver, along with the prediction portion of IGS rapid or ultra-rapid products.