Precise Point Positioning with Ambiguity Resolution using the Decoupled Clock Mode

摘要

The Decoupled Clock Model is a reformulation of the ionosphere-free code and phase Observation equations for GPS, which, when combined with the widelane-phase/narrowlane code observable, permits undifferenced ambiguity resolution of 86cm and 11cm ambiguities. The nature of the decoupled clock model implies a clock, or clock-like, parameter estimated for each observable for both satellites and receivers. Being general in nature, the decoupled clock model can be used with isolated receiver data for the purposes of Precise Point Positioning (PPP), albeit now with the capability for Ambiguity Resolution (AR). In addition to precise satellite coordinates, precise estimates of each observable clock must be used as fixed quantities in the PPP Solution. When applied to static PPP, there is little improvement provided by ambiguity resolution at the end of a 24-hour period. What ambiguity resolution does provide is the ability to reach similar levels of accuracy within much shorter Observation periods. With 30-second test data, after 60 minutes 90% of horizontal positions are at the two-cm level or better with AR, compared to ten centimetres without AR. In the data sets processed here, 50% of the horizontal positions are at the two-cm level after 10 minutes with AR. Vertical positions are less improved by ambiguity resolution, indicating further modelling improvements, such as low-elevation troposphere, may be required.