Flight evaluation of GPS precise point positioning for helicopter navigation

We reported development and assessment of a precise point positioning (PPP) software for land vehicular navigation in 2006. This paper presents one phase of the continued study at NDA for further extension of the software to helicopter navigation. For 3D users, the height-dependent tropospheric delay is a critical factor, and so the sophisticated correction models and parameter estimation strategies have to be investigated to mitigate the delay effect. Also, since the PPP results become available only after the filter convergence and the filter generally converges rather slowly, speeding up the convergence has to be taken special attention. In this paper we have proposed some new ideas to cope with these problems, and tested using GPS helicopter flight data in post-processing mode. With proposed techniques including the pseudo-observation concept, we have shown that point positioning accuracy at about decimeter level both horizontally and vertically has been achieved with improved convergence within about half an hour. We have also shown that the use of the high-rate (30-second) satellite clocks rather than the 5-minute clocks further improves positioning accuracy at sub-decimeter level in each 3D coordinate.