Evaluation of Systematic Differences Between the North American Vertical Datum of 1988 and Release 5 GOCE Product

Abstract:

The North American Vertical Datum of 1988 (NAVD 88) serves as the primary vertical reference control for the conterminous United States and Alaska. Implemented in 1991, this datum has been shown to disagree at over a meter with global gravity models (GGM’s) based on GRACE products. However, the resolution of such models was limited to about 600 km and larger scales for comparisons with GPS-derived ellipsoid heights on leveled benchmarks. In this study, GGM’s based on GOCE Release 5 are assessed. Given the increased resolution of these models, scales down to 150 km, an improved estimate of the systematic differences with NAVD 88 is possible. Such a model would serve as an a priori estimate of errors and greatly aid in development of hybrid geoid height models used to transform GPS observations into estimates of orthometric heights above NAVD 88. The National Geodetic Survey develops hybrid models using least squares collocation, which presupposes that the data are centered and stochastic and not systematic. In 2022, NGS will develop a replacement for NAVD 88 and future error models, such as the one presented here, will serve as a mechanism for datum transformation for backward compatibility to NAVD 88.