NOAA Guidelines for Establishing GPS-Derived Ellipsoid Heights

http://www.ngs.noaa.gov/PUBS_LIB/NGS-58.html

The following guidelines were developed by the National Geodetic Survey (NGS) for performing Global Positioning System (GPS) surveys that are intended to achieve ellipsoid height network accuracies of 5 cm at the 95 percent confidence level, as well as ellipsoid height local accuracies of 2 cm and 5 cm, also at the 95 percent confidence level.