The Online Positioning User Service: a Web Utility for Precise Geodetic Positioning in the Geosciences

Geoscientists often require precise positioning capability to support research. Accurate Global Navigation Satellite System (GNSS) positioning is a specialized skill involving expertise and fraught with accuracy-compromising nuances. With the goal of providing a robust and high accuracy positioning tool and enhanced access to the United States’ National Spatial Reference System (NSRS), the nation’s fundamental positioning infrastructure, NOAA’s National Geodetic Survey (NGS) developed the Online Positioning User Service (OPUS). OPUS is a free Web utility for processing user-submitted GNSS observations and producing geodetic coordinates referenced to both NSRS and a global reference frame. Relying on NGS’ national network of GNSS Continuously Operating Reference Stations (CORS), OPUS is a powerful and user-friendly tool for production and scientific research. OPUS is widely used in geomatics professions and holds great, yet not fully tapped, potential for research geoscientists requiring accurate positional information.

OPUS became operational in 2002 as a single point processing tool for multi-hour GPS occupations (OPUS-Static). Its capability has since evolved, adding the ability to process short (15 minutes) sessions (OPUS-RapidStatic) and to provide a solution sharing option. All OPUS variations have proven to be popular, with typical monthly submissions now numbering 40,000.

In 2014, NGS released a network version of OPUS, OPUS-Projects, the focus of this discussion. Although other versions of OPUS process a single GNSS occupation per submission, OPUS-Projects offers rigorous geodetic network analysis and processing capability by assembling and processing GNSS observations collected over time and at multiple locations. Least squares geodetic network adjustment of included observations results in an optimal set of station coordinates, including their uncertainties and graphical statistical plots, derived from user-submitted observation data, CORS observation data and coordinates, satellite ephemerides, and models. Users have the ability to configure the processing, including tropospheric modeling, definition of observation sessions, network design, adjustment constraints, station descriptive information, and integration with passive geodetic control.