On the Spectrum of the GPS DD-Ambiguities

One of the major problems in processing GPS phase observations is estimating the double-difference (DD) ambiguities as integers. Based on carrier phase data only, short observational time spans result in strongly correlated ambiguities and in very elongated ambiguity confidence ellipsoids. As a result the estimation of the integer least-squares ambiguities becomes an extremely time consuming task, when traditional search-methods are applied. In this contribution, it will be shown both analytically as well as numerically, that this can be explained by the distinctivediscontinuity that is present in the spectrum of conditional variances of the DD-ambiguities. In [1] a method has been introduced, that allows an efficient estimation of the integer ambiguities over short observational time spans. This method removes the discontinuity from the spectrum, thereby returning transformed ambiguities that are much less correlated and that show a dramatic improvement in precision. In this contribution the performance of the method will be demonstrated for a number of specific cases.