Dru A. Smith

Rigorous Estimation of Local Accuracies

This technical note introduces a rigorous calculation of “local accuracies.” The term local accuracies refers to the relative error between two arbitrary points (uncertainty of one point with respect to the other), expressed in a local horizon three-dimensional reference frame ( e,n,u ) , that were connected using any geodetic-surveying methodology [optical procedures, global positioning system (GPS), etc.]. It is calculated as a function of the full global Cartesian variance-covariance matrix of the ( x,y,z ) coordinates of the points defining the spatial network.

Taking the “Boulder” Step From Static to Dynamic Geoid: 2009 Workshop on Monitoring North American Geoid Change; Boulder, Colorado, 21–23 October 2009

As coastal communities are increasingly affected by sea level rise and flooding from extreme weather events, and as less evident (yet significant) tectonic shifts reshape the North American continent, the need for elevation data that are accurate, consistent, updated, and easily accessible has become critical. Currently, however, the vertical datums in North America are defined by tide gauge and leveling observations, which inevitably become outdated and are costly to replace or repeat. Therefore, two North American governments (Canada and United States) have resolved that the next generation of their national vertical datums will be geoid- based and accessible through Global Navigation Satellite System (GNSS) technology. To adequately serve as the reference surface for a future vertical datum, the geoid must be modeled accurately and its changes over time must be monitored. But what mix of tools and techniques could fulfill this requirement? To address this question and to plan for a campaign to monitor North American geoid change, experts from North America (including United States, Canada, and Mexico) and Europe specializing in satellite and terrestrial gravimetry as well as satellite positioning convened in Colorado.

In Pursuit of a cm-Accurate Local Geoid Model for Ohio

As part of its strategic plan for 2008–2018 [The NGS Ten Year-Plan, Mission, vision and strategy, 2008–2018], the National Geodetic Survey has resolved to engage in activities which would allow for the development of a 1-cm accurate national gravimetric geoid for the conterminous US. In this regard, the Ohio Department of Transportation has been collaborating with the OSU SPIN Laboratory in height modernization activities for the state of Ohio. Presented in this paper are the results of an investigation used to evaluate the quality of gravity and height data needed to produce a cm-accurate geoid in Ohio.