World Geodetic System

The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also describes the associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM). The standard is published and maintained by the United States National Geospatial-Intelligence Agency. History Efforts to supplement the various national surveying systems began in the 19th century with F.R. Helmert's famous book Mathematische und Physikalische Theorien der Physikalischen Geodäsie (Mathematical and Physical Theories of Physical Geodesy). Austria and Germany founded the Zentralbüro für die Internationale Erdmessung (Central Bureau of International Geodesy), and a series of global ellipsoids of the Earth were derived (e.g., Helmert 1906, Hayford 1910/ 1924). A unified geodetic system for the whole world became essential in the 1950s for

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Covariant formulation of relativistic mechanics

Miguel Alexandre Ribeiro Correia

Accretion disks surrounding compact objects, and other environmental factors, deviate satellites from geodetic motion. Unfortunately, setting up the equations of motion for such relativistic trajectories is not as simple as in Newtonian mechanics. The principle of general (or Lorentz) covariance and the mass-shell constraint make it difficult to parametrize physically adequate 4-forces. Here, we propose a solution to this old problem. We apply our framework to several conservative and dissipative forces. In particular, we propose covariant formulations for Hooke???s law and the constant force and compute the drag due to gravitational and hard-sphere collisions in dust, gas, and radiation media. We recover and covariantly extend known forces such as Epstein drag, Chandrasekhar???s dynamical friction, and Poynting-Robertson drag. Variable-mass effects are also considered, namely, Hoyle-Lyttleton accretion and the variable-mass rocket. We conclude with two applications: (1) The free-falling spring, where we find that Hooke???s law corrects the deviation equation by an effective anti???de Sitter tidal force and (2) black hole infall with drag. We numerically compute some trajectories on a Schwarzschild background supporting a dustlike accretion disk.

AMER PHYSICAL SOC2022

1999

New time-dependent slip inversion of Slow Slip Events: application to the 2006 Guerrero SSE

Mathilde Edmée Lucette Radiguet de la Bastaie

The 2006 Slow Slip Event in Guerrero, Mexico, is one of the world's largest SSE observed up to now. Thanks to the development of the Guerrero GPS network, the 2006 event was recorded at 15 continuous GPS stations that allowed a detailed study of the surface displacements produced by the event. Temporal variations of the displacement vectors, observed during the 2006 SSE, suggest a complex spatio-temporal evolution of slip on the plate interface. We developed a new method to model the spatial and temporal evolution of slip on the fault plane. We assume a functional form for the slip function on the fault plane, similar to the slip function defined by Liu et al. (2006) for kinematic source inversion of regular earthquakes. This slip function is parameterized by the slip amplitude, the initiation time of the slip, and the slip duration, which is the combination of an accelerating and decelerating rise time. The fault plane is divided in 42 subfaults of 78 km x 25 km each. The Green functions are calculated for a layered elastic half space. First, forward modeling tests show that the geodetic data are sensible to the location of the initiation slip patch, the propagation of the rupture and the duration of the slip. Second, using the same parameterization for the slip function, we invert for the slip amplitude, slip duration and rupture propagation velocity. We perform a linearized least-square inversion in the frequency domain. This new inversion procedure provides a continuous image of the spatial and temporal variatio

2009

Geodesy

Geodesy is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D. It is called planetary geodesy when studying other astronomic

Latitude

In geography, latitude is a coordinate that specifies the north–south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° a

Geodetic datum

A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame) is a global datum reference or reference frame for precisely representing

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Bases des références géodésiques, principe de mesure utilisé en localisation par satellites et de l'estimation de la qualité de positions GNSS (Global Navigation Satellites Systems).

ENV-140: Fundamentals of geomatics

Bases de la géomatique pour les ingénieurs civil et en environnement. Présentation des méthodes d'acquisition, de gestion et de représentation des géodonnées. Apprentissage pratique avec des méthodes topométriques et d'imagerie du territoire.

CIVIL-211: Geology

Les ingénieurs civils exercent leurs activités en constante interaction avec le sous-sol. Le cours de géologie donne aux étudiants les bases en Géosciences nécessaires à une ingénierie bien intégrée dans le contexte de notre planète.