Tightly Coupled Processing of Precise Point Position (PPP) and INS Data

This paper looks at the implementation and results from processing un-differenced GPS data (PPP) with Inertial Measurement Unit (IMU) data using a tightly coupled filter in an airborne environment. With the use of precise orbit and clock products, PPP has matured from a research topic to a practical GPS processing methodology. The major advantage of PPP GPS processing is that decimeter level accuracy can be achieved globally without any base station. The major drawback of PPP lies in the fact that the solution is slow to converge compared to conventional differential GPS. This can be a serious disadvantage for airborne missions with intermittent losses of lock or poor satellite geometry associated with turns. In fact, one of the principal time and cost constraints in conventional GPS-based airborne mapping lies in the necessity to maintain shallow bank angles on turns, typically less than 30 degrees. With a tightly coupled PPP/INS filter, results can significantly improve during periods of poor satellite geometry or after losses of lock. For this investigation, a tightly coupled PPP/INS filter was implemented in NovAtel's Inertial Explorer post processing software package and results from a variety of airborne missions are presented. Using this methodology, multiple data sets from an airborne environment were examined. Bank angles of 45 and 70 degrees were implemented on every turn within actual airborne surveys by removing (in software) lower elevation satellites during the turns. The results are then compared to a reference trajectory and the position and attitude degradation examined.