High Precision GPS Measurements

The objective of this project is to develop high precision GPS receivers by utilizing modernized GPS signals at L1, L2, and L5 frequencies to mitigate GPS measurement errors. For each successfully acquired and tracked GPS signal, a GPS receiver generates two receiver-satellite range observables: the code phase and the carrier phase measurements. Precision GPS solutions are obtained by exploiting both observables at all available frequencies to eliminate, reduce, or estimate various error sources. These error sources include signal propagation errors through the ionosphere and troposphere, satellite orbit and clock errors, receiver clock error, receiver noise, multipath error, hardware bias, and integer cycle ambiguities associated with the carrier phase observables. The project proposed an array of innovative methods to assess and mitigate these errors. Since the start of the project in March 2007, we made significant progress in three major areas: (a) Higher order ionosphere error temporal and spatial variations studies; (b) satellite orbit and clock error characterization; (c) modeling of troposphere error under severe weather conditions. The report summarizes the progress made in these three areas. The original document contains color images.