On carrier signal multipath effects in relative GPS positioning

Discusses errors in GPS carrier phase observations resulting from multipath interference. A mathematical model for multipath induced carrier phase errors is derived. It is shown that multipath can be monitored over short baselines by analyzing dual frequency measurements. Two related experiments are reported. The first example demonstrates that extreme multipath interference can render useless GPS observations for precise positioning applications. The 2nd example shows the danger of occurrence of long periodic multipath errors caused by conducting material in the immediate vicinity of the receiver antenna.