Integrated INS/GPS system for high precision navigation applications

The paper describes the combination of a Honeywell LASERNAV II ring laser gyro inertial navigation system (INS) and Trimble SSE GPS receivers. A software package for the strapdown system was developed using common terrestrial zero velocity (ZUPT) and coordinate update (CUPT) techniques. An Integrated GPS inertial position and attitude control system (IGIPACS) is built up in different levels. The first level is a separate operation of the GPS receivers and the INS. Here the INS-system is supported by GPS positions with an update rate of at the most 2 Hz. The GPS positions are evaluated by various types of applications (rapid-static, kinematic) with cm-accuracy. The INS is used to interpolate the positions between the update points with a rate of 50 Hz. In the second level the GPS positioning is supported by the INS system during losses of lock using the Kalman filter technique (cascade integration). Within this algorithm differential GPS is applied using double difference code solutions. Numerous tests were made using a station wagon, sometimes with an array of three or four antennas, as well as an aircraft supporting the determination of a digital terrain model with laser scanner and radar altimeter. Problems and differences in terrestrial and airborne applications are outlined. The accuracy of the system, its potential and further steps are discussed