Are there formal accuracy estimates for GEOID99?
There are no formal accuracy estimates for GEOID99. The computation of the gravimetric residual co-geoid undulations from residual Faye gravity anomalies was done through a 1-D FFT representation of the spherical Stokes integral, which inherently contains no formal accuracy estimation. However, in the United States we have a fairly homogenous distribution of GPS-derived ellipsoid heights (in the NAD 83 datum) co-located with leveled Helmert orthometric heights (in the NAVD 88 datum) and these data are used to control long wavelength errors in the geoid model as well as providing an accuracy check. It is found, nationwide, that we are able to reproduce GPS/level derived geoid undulations with our GEOID99 model to the +/- 4.6 cm level. The source of this disagreement is both the error in GPS heights as well as geoid and leveling errors. Separation of the errors is difficult, but preliminary analysis indicates that +/- 2.5 cm of that is geoid error. Dr. Dennis Milbert performed some preli
