One of the major challenges in resolving ambiguities for longer baselines is the presence of unmodelled ionospheric delays. In this paper, we describe a new ionospheric approach that does not rely on the convergence of an ionospheric parameter, and that instantaneously nullifies the effect of the differential ionospheric delay in an ambiguity search process. The performance of the ionosphere-nullification approach was demonstrated using the data recorded at a 1 Hz data rate at a pair of base stations on either side of the Bay of Fundy in eastern Canada and on the ferry boat, at the terminals of an approximately 74 km ferry route, on 21 May 2004. The UNB RTK software was enhanced to perform this study. For both static and kinematic tests over the longer 74 km baseline, a few millimeter mean differences were observed in each Cartesian component, and the comparison 1σ noise level was at the few centimeter level. For further enhancements of the UNB RTK software in near future, two issues are discussed in this paper, including a filtering process on the ionosphere observables to reduce the effects of multipath and an estimation of the residual zenith tropospheric delay to remove its residual effects.
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