Some Pitfalls to be Avoided in Combining Simultaneous GNSS Networks

Abstract

Assume that a network, in this case a network of GNSS observables, has to be adjusted and one likes to split it into subnetworks, and adjust them separately; then the subnetworks have to be recomposed by using the cross observations connecting their points. Ideally, this should be done in a way such that the final solution is the same as that provided by a rigorous joint solution of all the observations. The problem is classical and has a rigorous solution, called Helmert blocking, for terrestrial networks, where the observations are typically uncorrelated. For the GNSS networks thought, where many times the phase double differences are treated as observations, the hypothesis of linear independence is by definition inconsistent: this gives rise to blunders in the solution that are illustrated in the paper by numerical examples. An alternative solution is envisaged to overcome these drawbacks.