The assessment of OPUS-Static in limited CORS area based on session duration

The Online Positioning User Service (OPUS) is a suite of Web-based tools used to process GPS data. It is a popular tool for surveyors, engineers, and the academic communities that offer precise positions from global positioning system (GPS) observations. OPUS offers point position processing via online services worldwide. For many developed countries, the extensive numbers of available Continuously Operating Reference Stations (CORS) is facilitated in obtaining accurate results. However, the accuracy of this tool has to be checked in remote areas or in areas where there are limited base stations available. This research focuses on checking the accuracy of the observation session from 2 to 15 hours in the area in which CORS is insufficient and comparing them with OPUS published accuracies and precision. 16-h-duration GPS data files collected on 13 passive stations in Duhok area using Leica viva GNSSN, GS10 in static mode. Then, these data files were windowed into sessions ranging from 2 to 14 hours in duration. The windowed files were processed in OPUS-static, and the resulting coordinates at each station were compared with the coordinates averaged and achieved 1 to 8 mm in precision which has been considered as a true value. The results showed that the obtained accuracies were not complied with OPUS published results. While for the windowed sessions, the achieved precision was in the range of 1 mm to 30 mm.