The mount Cameroon height determined from ground gravity data, global navigation satellite system observations and global geopotential models

AbstractThis paper deals with the accurate determination of mount Cameroon orthometric height, by combining ground gravity data, global navigation satellite system (GNSS) observations and global geopotential models. The elevation of the highest point (Fako) is computed above the WGS84 reference ellipsoid. The geoid undulation and the height of Fako above mean sea level were also determined. Ground data consist of a sparse gravity net recorded around 1950, densified with recent data collected on and around the mountain. GNSS data consist of ellipsoidal elevations and precise horizontal point coordinates computed from GPS satellites observations, and those of other systems orbiting around the Earth. Global geopotential models involved are a hybrid model EGM-GGM and the recent Earth Gravity Model EGM2008. The method used appears more flexible than spirit leveling, which is too expensive, time consuming, difficult and of very low accuracy in mountainous areas, where the topography is very rough. Mount Cameroon, which is the highest summit in central and western Africa, is now known to culminate at 4037.7 ± 0.7 m above sea level. This height is nearly 60 m less than the approximate value of 4095 m published by the National Institute of Cartography.

Gravity Data Interpretation in the Northern Edge of the Congo Craton, South-Cameroon

Gravity data in the southern Cameroon are interpreted to better understand the organization of underlying structuresthroughout the northern edge of the Congo craton. The Bouguer anomaly maps of the region are characterized by an elongated trending trending negative gravity anomaly which correspond to a collapsed structure associated with a granitic intrusion beneath the cente center of the region r of the region of the region and limited by fault systems. �e applied 3�D gravity modelling and inversion in order to obtain the 3D density structure of the area. Our result demonstrated that observed gravity anomalies in the region are associated to tectonic structures in the subsurface. The resulting model agrees with the hypothesis of the existence of a major continental collision zone between the Congo Craton and the Pan�African belt. The presence of deep granulites structures in the northern part of the region expresses a continental collision

Interpretação gravimétrica na Borda Norte do Cráton do Congo, Sul de Camarões

Gravity data in the southern Cameroon are interpreted to better understand the organization of underlying structures throughout the northern edge of the Congo craton. The Bouguer anomaly maps of the region are characterized by an elongated SW-NE trending negative gravity anomaly which correspond to a collapsed structure associated with a granitic intrusion beneath the center of the region and limited by fault systems. We applied 3-D gravity modelling and inversion in order to obtain the 3-D density structure of the area. Our result demonstrated that observed gravity anomalies in the region are associated to tectonic structures in the subsurface. The resulting model agrees with the hypothesis of the existence of a major continental collision zone between the Congo Craton and the Pan-African belt. The presence of deep granulites structures in the northern part of the region expresses a continental collision.Um conjunto de dados gravimétricos, provenientes do sul de Camarões, foram interpretados para o melhor entendimento das estruturas em sub superfície na borda norte do Cráton do Congo. Os mapas de anomalia Bouguer desta região foram caracterizados por uma anomalia gravimétrica negativa de direção SW-NE, que corresponde a uma estrutura de colapso associada com uma intrusão granítica, abaixo do centro desta região, e que está limitada por um sistema de falhas. Foram utilizados métodos de modelagem gravimétrica 3 D e inversão, para se obter uma estrutura densa 3-D desta área. Os resultados demonstraram que as anomalias gravimétricas observadas na região estão associadas com estruturas tectônicas em sub superfície. O modelo resultado está em consonância com a hipótese de existência de uma zona de colisão continental principal entre o Cráton do Congo e o Cinturão Pan-Africano. A presença de estruturas granulíticas profundas na borda norte desta área indica uma colisão continental

The Local Geoid Model of Cameroon: CGM05

This paper deals with the geoid determination in Cameroon by a gravimetric solution. A number of data files were compiled for this work, containing about 62,000 points on land and ocean areas and also including data derived from satellite altimetry. A hybrid global geopotential model (EGM-GGM) supplied the longer wavelength components of this geoid model, CGM05. This global model is obtained by adjusting the GRACE model GGM02C to degree and order 360 using the harmonic coefficients of the model EGM96 beyond the maximal degree 200 of GGM02C. The medium wavelength components were computed using the best gridded residual gravity anomalies, by integration in Stokes’ formula. The digital terrain model GLOBE contributed to its short wavelength components. The residual terrain model (RTM) was applied to first determine a quasi-geoid model. This intermediate surface was converted to the geoid using a grid of simple Bouguer gravity anomalies. The validation of CGM05 is based on comparisons to global and regional geoids. A GPS/levelling geometric geoid computed in a small part of the target area shows that the absolute accuracy of this local geoid model is 14 cm. After a four-parameter fitting to the GPS/levelled reference surface, this absolute accuracy reduced to 11 cm

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Dubinsko kartiranje na temelju gravimetrijskih podataka na području sjevernog ruba Kongo kratona, južni Kamerun

In this work, the subsurface structures in a part of the northern edge of the Congo craton in South Cameroon between the latitudes 2° 30\u27 to 4° 30\u27 N and the longitudes 11° to 13° E, has been estimated by the interpretation of gravity data. For quantitative interpretation of the sources of the anomaly, a 3D density model of the upper crust was designed by means of forward modelling and inversion constrained by surface geology and results from Euler deconvolution and spectral analysis methods. The Bouguer anomaly map of the area is characterized by elongated SW–NE trending negative gravity anomaly which correspond to a collapsed structure associated with a granitic intrusion beneath the center of the region and by various gravity highs associated with an uplift of the Pan-African basement in the north and delimited by a strong gradient in relation with the tectonic boundary between the Congo craton and the Pan-African belt. Our result demonstrated that tectonic structures associated to observed gravity anomalies in the region were put in place during a major continental collision.U ovom radu se pomoću gravimetrijskih podataka procjenjivala struktura kore u dijelu sjevernog ruba kratona Konga u južnom Kamerunu, smještenom između 2° 30\u27 i 4° 30\u27 N te 11° i 13° E. U svrhu kvantitativne interpretacije uzročnika anomalije napravljen je 3D model gustoća gornje kore na temelju modeliranja i inverzije. Rezultati inverzije su ograničeni površinskim geološkim podacima i rezultatima Eulerove dekonvolucije i spektralne analize. Kartu Bouguerovih anomalija istraživanog područja karakterizira izdužena negativna gravimetrijska anomalija pružanja SW–NE, koja je uzrokovana urušenom strukturom povezanom s intruzijom granita u središnjem dijelu područja. Različite pozitivne anomalije povezane su s izdizanjem Panafričke podloge u sjevernom dijelu, a omeđene su velikim gradijentom uzrokovanim tektonskom granicom između kratona Konga i Panafričkog pojasa. Rezultati pokazuju da su tektonske strukture koje uzrokuju opažene gravimetrijske anomalije (na istraživanom području) nastale tijekom kolizije (sudara) kontinenata

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International audienceGuidelines and tools are easier to understand and use when presented through examples. The SSK provides a variety of standardized resources in a meaningful context, delivered by research use cases : the « scenarios ». FULL TEI TEI is the SSK underlying data model, designed to maximize scenario reuse and customization

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