Dual-Frequency Static GNSS Positioning Under Open-Sky Conditions: OPUS Vs. AUSPOS

This study presents a comprehensive evaluation of two widely used free online Global Navigation Satellite System (GNSS) processing services, namely the Online Positioning User Service (OPUS) and the Australian Positioning Open Service (AUSPOS), for dual-frequency static positioning under open-sky desert conditions. The analysis was conducted using ten 24-hour GNSS datasets collected from geographically distributed stations across Libya using dual-frequency receivers operating in static mode. Two processing configurations were investigated: OPUS (GPS-only) and AUSPOS (GPS-only). Positioning performance was evaluated as a function of observation duration, with data segments ranging from 1 to 24 hours. The fully converged 24-hour solution generated by each service was adopted as the reference benchmark for accuracy assessment.
The results indicate noticeable differences in convergence behavior and short-session positioning performance between the two services. OPUS demonstrated superior accuracy during the early observation periods, achieving approximately 31 cm three-dimensional (3D) accuracy after one hour of observation, whereas AUSPOS achieved approximately 83 cm under the same conditions. As the observation duration increased, the positioning accuracy of both services improved substantially, with both solutions converging toward millimeter-level precision. Overall, OPUS exhibited faster convergence and more stable positioning performance than AUSPOS, particularly for short observation sessions. The findings highlight the significant influence of processing strategy and observation duration on high-precision GNSS positioning performance and provide valuable guidance for selecting appropriate online processing services for static surveying and geodetic applications.