Shortening the Convergence Time of Wide-Area Real-Time Kinematic Solutions

In recent years, thanks to a series of improvements in hardware, data transmission, operating procedures, and data analysis techniques, reliable real-time kinematic solutions of decimeter and even sub-decimeter precision have become possible in Wide-Area Network RTK, for both long-baseline differential positioning and absolute point-positioning (i.e., using the roving receiver's data and precise orbits and satellite clock corrections as the only information). These solutions have applications in land surveying, in geophysical research, and also in remote-sensing marine, land, and airborne campaigns, enabling more precise and reliable navigation for a variety of commercial, scientific, mapping, and engineering purposes, when obtaining high precision results in real-time or near-real time is a must (as in detecting the waves of an incoming tsunami while still far from land with GNSS receivers on buoys anchored far from the coast). A major limitation common to all precise Wide-Area solutions, but particularly important with real-time and near-real time ones, is that it can take quite long before enough data have been collected, and there has been a sufficiently large change in the geometry of the satellites in view, to achieve full precision. There are several ways of speeding up the convergence of a solution. Among others: resolving the carrier phase ambiguities with or without precise ionospheric corrections, and using the slow-varying mean sea level (after averaging out ordinary wind-driven waves) as a constraint on the solution. In this paper, the author describes some of those techniques and presents examples of their use, discussing their usefulness and limitations.