Range errors in global positioning system during ice cloud and snowfall periods

Results from a global positioning system (GPS) measurement campaign conducted during March 1989 on a baseline of 13.1415 km length show a relatively large discrepancy in the adjusted baseline height component during ice cloud and snowfall periods. These experimental observations have stimulated the development of a propagation-prediction model to investigate the performance of GPS carrier beat phase measurements during ice cloud (predominantly present above the freezing level) and snowfall precipitation periods. Theoretical results revealed that even for extremely high ice cloud volume concentrations and for snowfall rates up to 20 mm/h the estimated phase delay, if identical at the two receiver sites, has negligible effect on the recovery of the vector baseline components. However, due to the localized nature of many snow storms and the nonuniform spatial cover of ice clouds, the differential effects between two distant receiver sites can become important for precise relative GPS applications. Finally, the model demonstrates that a differential phase delay of about 4.6° at zenith which is to be expected under adverse storm conditions may explain the range of experimentally observed discrepancies in the relative baseline height component