This is the first in a series of four articles on establishing North American Vertical Datum of 1988 (NAVD 88) heights using the Global Positioning System (GPS). This article discusses the basic concepts of GPS-derived heights; the second article will discuss NGS’ guidelines for establishing 2- and 5-cm GPS-derived ellipsoid heights; the third article will address procedures for analyzing GPS results to ensure the standard has been met; and the fourth article will briefly discuss basic procedures that need to be followed for establishing NAVD 88 GPS-derived orthometric heights that meet the 2- and 5-cm standards.
Over the past decade, GPS surveying techniques have proven to be so efficient and accurate that they are now routinely used in place of classical line-of-sight surveying methods for establishing horizontal control. Understandably, interest has been growing in using GPS techniques to establish accurate vertical control. Progress, however, had been hampered due to difficulties in obtaining sufficiently accurate geoid height differences to convert GPS-derived ellipsoid height differences to accurate orthometric height differences.