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An Uncertainty Analysis for the Calibration of GNSS-Based Vehicle Speed Meters

In the field of traffic speed measurement, thanks to the accuracy claimed by the manufacturer of Global Navigation Satellite System (GNSS) receivers (about 0.1 km/h) they are increasingly used as reference equipment for calibration of speed measurement instruments. In order to assure the traceability of the measurement results also the GNSS should be calibrated according to the rules of ISO/IEC 17025 standard and complying with the ILAC (International Laboratory Accreditation Cooperation) policy on the traceability of measurement results. Unfortunately, in this context, worldwide there is a strong limitation about the compliance to the ILAC policy. In this paper, an analysis about the suitability of an experimental calibration method for GNSS speed measurement systems has been carried out. Considering all the measurement uncertainty contribution a sensitive analysis has been made in order to understand which are the limits and/or the applicability of this calibration methodology in a speed range from 30 to 250 km/h, in compliance with the ISO/IEC 17025 and ILAC policy.