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A brief (historical) review on definitions and applications of the geoid

In the last 200 years, various definitions of the geoid have been given. One of the given definitions is that it is the surface of constant potential W_0. The term geoid is used synonymously for few similar surfaces (such as quasi-geoid or hybrid quasi-geoid), and this depends on particular scientific or practical application. One of its main applications is in the realization of the height reference systems (HRS) as the geoid is the reference surface for physical heights. The problem arises, as it will be presented, in the materialization of the geoid as this can be done in an almost infinite number of ways for different time-epochs. Therefore, several types and kinds of geoids are commonly used without clear distinctions between their main properties. In geodesy, several important scientific projects are currently closely related to the geoid. One of the main initiatives is related to the International Union of Geodesy and Geophysics adoption of the World Height System and decades of attempts to establish and practically realise the International Height Reference System. On the regional spatial scale, few countries are working on the modernization of their HRS and did already adopt gravimetric geoid-based HRS. The accuracy of geoid models has increased dramatically since their's first realizations and is today at 1-3 cm level in most Western countries, although even sub-cm accuracy level seems to be reachable within the decade. So the initiative and general objective are to have only unified global HRS defined by W_0, although geoid is now different in each country of the world. In order to emphasize the importance of precise and consistent usage of the geoid, a review is given on definitions, historical development and applications of the geoid models worldwide.

geoid ; definition ; normal heights ; orthometric heights ; vertical datum ; quasi-geoid ; RCR ; LSMSA (KTH) ; height reference system

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