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.

Accurate gravity anomaly interpolation: a case-study in cameroon, central africa

Many treatments in geodesy and geophysics require regularly gridded gravity anomalies. The gridding of gravity data needs interpolation. For the predicted data to be accurate, the smoothest type ofgravity anomaly should be used along with the most indicated prediction method. This paper presents the comparison of various prediction methods applied on different types of gravity anomalies andconsidering the relative geological complexity of the study area. Many algorithms are tested and the suitability of each type of anomaly and each prediction method discussed in a case-study in Cameroon (Central Africa), using a set of 43,000 gravity data points to determine the must accurate prediction technique

Programme Fortran 77 d\'ajustement du modèle de géoïde EGM96 sur la surface de référence de points GPS/nivelés.

Les altitudes recherchées lors du nivellement sont mesurées par rapport à une surface de référence : le géoïde. Le nivellement géométrique est un processus long et onéreux, on préfère désormais procéder par nivellement GPS (Global Positioning System). La surface de référence est alors réalisée en ajustant le modèle de géoïde dont on dispose sur la référence obtenue d'un ensemble de points GPS/nivelés. Les modèles de géoïde locaux ne sont pas encore disponibles dans toutes les régions. Un modèle de géoïde global peut alors être utilisé. Cet article présente un programme exécutable sur un environnement Fortran, qui permet d'ajuster le modèle de géoïde global le plus utilisé EGM96 par moindres carrés dans une région, à partir d'une modélisation par régression linéaire. Il fournit en sortie tous les résultats dans un fichier texte. Le programme crée également une grille de géoïde ajusté dans laquelle l'utilisateur peut interpoler l'ondulation ajustée en un nouveau point où il vient de faire des mesures GPS. Les résultats d'un test à partir des données sur le Cameroun montrent les résidus escomptés, avec un écart-type 0,08 m. Ce programme présente ces avantages qu'il utilise la valeur exacte de l'ondulation EGM96 en chaque point du fichier d'entrée de l'utilisateur et a un temps d'exécution optimal quel que soit le nombre de points pris en compte.Heights obtained from levelling are determined above a reference surface: the geoid. Spirit levelling is a timeconsuming high cost process. An alternative leveling process by GPS (Global Positioning System) is now used instead. The reference surface is therefore realised by fitting the available geoid model to the surface obtained from a set GPS/levelled points. However, local geoid models are still not available in many parts of the world. A local geoid can be replaced by a global one to achieve this. The program presented in this paper is executable on a Fortran surrounding and it permits to fit the must widely used global geoid EGM96 in the least squares sense in a region, from a linear regression modelling. The results are presented in an output text file and an output grid where the user can interpolate the adjusted geoid undulation at a point where he made new GPS measurements. An experimental test obtained form data in Cameroon produced reasonable residuals, with a standard deviation of 0.08 m. Some advantages of using this program are that it computes the exact value of the EGM96 geoid undulation at all points of the user's input file and its execution is very fast, regardless the number of input data points. Keywords: Ajustement, nivellement, géoïde, moindres carrés, interpolation; Fitting, levelling, geoid, least squares, interpolation. Journal des Sciences Pour l\'Ingénieur. Vol. 9 2008: pp. 11-2

Estimating gravity field and quasi-geoid in Cameroon (CGM20)

In this paper, the computation of the new gravimetric quasi-geoid of Cameroon based on some recent global geopotential models and a detailed Digital Terrain Model (DTM) of the area is presented. Besides gravity data supplied by the Bureau Gravim´etrique International (BGI) new data have been collected by the National Institute of Cartography (NIC) of Cameroon and used in the computation. Three different quasi-geoid models have been obtained based on three different global models, namely GOCE-dir5, EGM2008 and XGM2019e_2159. The wellknown remove-compute-restore technique has been applied and Fast Collocation has been used for estimating the residual quasi-geoid component from gridded gravity data. The comparisons with Global Navigation Satellite System/levelling (GNSS/levelling) data distributed over the Cameroon territory show that some improvements have been obtained either with respect to the global model solutions and to previous local estimates computed in the past

3-year results of the German nationwide survey on eye injuries caused by fireworks

Background On festive days worldwide eyes are severely injured by fireworks. The data on the number and severity are to date not registered in Germany. Objective How frequent are firework-induced injuries in Germany, who are the affected, how serious are the injuries, which forms of treatment are necessary and how frequent are accompanying injuries? Method A German nationwide online-based survey was carried out in all inpatient eye departments and data over the last 3 consecutive years were descriptively analyzed. Results From New Years Eve 2016/2017, when 41 eye departments sent in data, the participation could be increased to 51 eye departments in 2018/2019. More than one third (33-39%) of all 1356 patients over 3 years were minors, 60% were younger than 25 years old and roughly 60% of patients were injured as bystanders or in an unclear situation. In total 25% of all eye injuries were considered severe and required inpatient treatment. Accompanying injuries of the other eye, the face and hands were more frequent in minors than in adults. Eyeball ruptures were reported in 10 minors and 38 adults over the 3 years. Conclusion Particularly minors and bystanders need better protection