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TitreDemystifying the vertical datum in Canada: A case study in the Mackenzie Delta
AuteurVéronneau, M
Source 2006, 24 pages (Accès ouvert)
LiensOnline - En ligne (PDF, 2 MB)
ÉditeurRessources naturelles Canada
Documentdocument interne
Mediaen ligne; numérique
Référence reliéeCette publication est une traduction de Véronneau, M; (2006). Démythification du plan de référence altimétrique au Canada : Une étude de cas dans le delta du Mackenzie
ProvinceTerritoires du Nord-Ouest; Yukon
SNRC106M; 106N; 106O; 116A; 116B; 107; 117
Lat/Long OENS-140.0000 -130.0000 70.0000 67.0000
Sujetsgéodésie; géodésie par satellite; géophysique; géomathématique
Illustrationssketch maps; tables; formulae
Résumé(disponible en anglais seulement)
Surveyors are currently going through a transition period for the determination of heights. Over the last few hundred years, the sole technique for precise height determination was spirit leveling. Today, surveyors also have the capability of determining accurate heights using space-based technologies (e.g., GPS) in a more efficient and cost-effective manner. While the leveling technique gives surveyors precise heights above mean sea level when measurements are tied to a benchmark, space-based positioning relates heights to a geometric reference surface (ellipsoid) representing the general shape of the Earth. Unfortunately, the latter does not have any physical meaning (i.e., water could flow up-hill). Therefore, a correction is required to relate ellipsoidal heights to the mean sea level. This is done by using a geoid model, which describes the separation between the ellipsoid and geoid. The geoid is the equipotential (level) surface describing mean sea level at rest.
When using either leveling or space-based positioning for height determination, surveyors require a vertical datum (reference surface), which allows a homogeneous height system at the national, continental or global scale. There may be only one practical definition of a vertical datum (mean sea level); however, its realization will vary as a function of the input data used to model it. This is where complications arise for surveyors: each new realization brings along a different, but generally more accurate datum than the previous one. More recently, the complications were compounded when geoid models became routinely available allowing GPS surveyors to measure significant mismatches between the geoid-derived datum and the distorted leveling-defined Canadian Geodetic Vertical Datum of 1928 (CGVD28).