GPS orbit determination using several reference

GPS is used in many situations and the accuracy of measurement satisfies various services in several fields. However the improvement of accuracy is requested in many fields. For precise positioning by GPS, it is necessary to estimate high accuracy orbits of GPS satellites. Although orbits of GPS satellites are calculated from ephemeris, the orbits do not correspond with actual orbits. Therefore, we used several reference stations and calculated the orbits by the following new algorithm; inverse GPS and RARR (range and range rate). Inverse GPS means that reference stations are considered as satellites and satellite as receiver. It is mainly used to trace animals or cars. RARR is the method of orbit estimation of other satellites and we use range rate to calculate the satellite orbit. In inverse GPS, we could calculate the orbits more accurately than the orbits from ephemeris. In RARR, we showed an effectiveness of our method.