The inter-American metrology system (SIM) common-view GPS comparison network

The inter-American metrology system (SIM) consists of national metrology institutes in 34 member nations located throughout North, Central, and South America, and the Caribbean region. Currently, at least ten SIM laboratories pursue time and frequency metrology, and are responsible for maintaining the national time and frequency standards for their respective countries. To benefit these laboratories and advance metrology in the SIM region, we have developed a measurement network to continuously intercompare these standards and to make the data readily accessible to all SIM members. This network utilizes the multi-channel common-view GPS technique and the near real-time exchange of data via the Internet. This paper discusses the challenges of implementing the SIM comparison network, and provides a technical description of the measurement system supplied to participating laboratories. It describes the method used to calibrate the SIM measurement systems, and describes how the measurement results are processed and reported to the laboratories. It presents data collected from comparisons between the national frequency and time standards located in Canada, Mexico, and the United States. It validates these data by comparing them to data collected from previously established time links. It concludes with a discussion of the measurement uncertainties.