NAVD88 Orthometric Height Determination Utilizing the California Real Time GPS Network

Cecilia Whitaker, Gregory A. Helmer, Yehuda Bock, Kari J. Launen and David E. Morgan

Abstract:	The California Spatial Reference Center (CSRC), in collaboration with the Scripps Orbit and Permanent Array Center (SOPAC) at University of California, San Diego, has completed numerous height modernization projects following the standards and specifications defined for the National Height Modernization Program, by the National Geodetic Survey. The continued demand for height modernization survey data, combined with advances in GPS processing and wireless data communication, led to the subject project utilizing the capability of the California Real-time Network (CRTN). This continuous GPS (CGPS) network utilizes real-time 1Hz data streams flowing through the SOPAC archive from more than 80- stations in southern California. The purposes of this project included testing the application of modern real-time GNSS surveying methods to high-precision geodesy, and to obtain critical data needed to analyze a proposed accuracy model for the national geoid. These purposes were accomplished by collecting data for establishing GPS-derived North American Vertical Datum of 1988 (NAVD88) orthometric heights on about 46 passive stations (National Geodetic Survey (NGS) first order bench marks) in Southern California. This work is part of CSRC’s goal to establish NAVD88 elevations on CGPS stations. Ultimately, this network of CGPS sites, with NAVD88 elevations, will become the foundation of a sustainable geodetic reference network for the California Spatial Reference System (CSRS). Such CGPS sites are critical to maintaining the vertical component of the CSRS, as they provide the ability to efficiently maintain the network (and other) orthometric heights using GNSS survey methods in combination with a high-precision national geoid model and corrector surfaces. This observation campaign was also part of a demonstration to test the viability for National Height Modernization surveys using the Pocket GPS Manager (PGM) software, developed by CSRC for NGS, and the functionality of CRTN. The GPS observations were collected in 2 five-hour sessions while connected to the CRTN server through a PDA cellular phone with the Geodetics RTD Rover software. Observations and 1 Hz positions were computed instantaneously (once per second) and stored at the server using Inverse Instantaneous Network RTKTM procedure, and streamed to the PDA. Single-epoch position statistics were computed at the server and running statistics were computed on the PDA. The accumulated PDA statistics were compared to positions computed by two on-line services, OPUS and SCOUT, as well as comparison to two post-processing procedures. The final GPS geodetic positions were converted to orthometric heights using the NGS Geoid ’03 model and compared to published NAVD88 elevations. The differences in GPS-derived orthometric heights to NGS first order elevations were examined to determine an accuracy estimate of the Geoid ’03 model in the project area.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2155 - 2162
Cite this article:	Whitaker, Cecilia, Helmer, Gregory A., Bock, Yehuda, Launen, Kari J., Morgan, David E., "NAVD88 Orthometric Height Determination Utilizing the California Real Time GPS Network," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2155-2162.
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