Interpreting OPUS-Static Results Accurately
Publication: Journal of Surveying Engineering
Volume 142, Issue 4
Abstract
The Online Positioning User Service (OPUS) operated by the National Geodetic Survey (NGS) has consolidated into a very attractive tool for surveyors, engineers, and the academic community to procure precise/accurate positions from global positioning system (GPS) observations. The OPUS utility continues to be improved since it was successfully launched in 2000. In general, each update results in better reliability of the precision and accuracy of OPUS solutions. However, necessary software modifications could also introduce certain biases, some significant, complicating the interpretation of OPUS results, particularly for applications that rely on high-accuracy absolute positions. This article concentrates on the interpretation of OPUS-Static solution reports primarily in relation to the transformation of reference frames and geoid models, which are two basic scientific ingredients in practical geodetic-surveying enterprises. One-year continuous GPS observations collected at a landslide site in Puerto Rico were uploaded to OPUS-Static on April 20, 2011; October 30, 2013; and April 29, 2015. The OPUS solutions obtained at these three dates were compared. This case study indicates that very considerable changes in orthometric height and horizontal coordinates could occur among OPUS outputs processed at different dates. OPUS users who focus on absolute positional coordinates should pay special attention to the periodic updating of reference frames and geoid models by NGS.
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Acknowledgments
The authors thank their NGS colleagues R. Foote, S. Hilla, D. Martin, and M. Schenewerk for reviewing the draft of the manuscript and for their comments and suggestions. This study was partially supported by a National Science Foundation (NSF) Faculty Early Career Development Program (CAREER) award (EAR-1229278), a NSF Major Research Instrumentation Program (MRI) award (EAR-1242383), and a NSF Transforming Undergraduate Education in Sciences (TUES) award (DUE-1243582). The authors are also grateful for the detailed observations and remarks of four anonymous reviewers that greatly improved and enhanced the comprehension of the final version of the manuscript.
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Published In
Journal of Surveying Engineering
Volume 142 • Issue 4 • November 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Dec 1, 2015
Accepted: Feb 19, 2016
Published online: Mar 29, 2016
Discussion open until: Aug 29, 2016
Published in print: Nov 1, 2016
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