The comparative DG accuracy analysis of a land based MMS using LC and TC INS/GNSS inetegration schemes

The most commercially available INS/GPS integration strategy is known as the loosely coupled (LC) scheme in which the GPS derived positions and velocities are integrated with the INS derived navigation information. The LC takes advantage of a simpler and more flexible architecture to derive navigation information, but the limitation is that the GPS KF will not provide position and velocity solutions as position and velocity updates for the INS KF if less than four satellites are tracked by the GPS receiver. Another commonly available integration strategy is known as tightly coupled (TC) scheme, which processes GPS raw measurements rather than the GPS navigation information to execute measurement updates. It performs well even if less than four satellites are tracked. In the TC, there is only one KF, which processes the accelerations and angular rates from the inertial sensors for navigation. Additionally, the KF also processes the pseudo - range, pseudo-range rate and carrier phase measurements from the GPS receiver. These measurements are used by the filter not only to estimate the navigation solutions, but also the inertial sensors correction parameters, which are used to compensate for the errors of accelerometers and gyros. Therefore, this study aims at investigating the impact of LC and TC INS/GNSS integration schemes on DG accuracy using the land based MMS developed at Department of Geomatics of National Cheng Kung University. The performance analysis is conducted by performing DG with 70 to 80 checking points from those images taken kinematically via proposed MMS van using the POS solutions processed with LC and TC schemes with variable number of visible satellites and comparing with known coordinates of those checking points, respectively.