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MEDIDA DE ALTURAS CON GPS (medida sobre el nivel del mar) V. Corchete* Departamento de Física Aplicada Escuela Politécnica Superior – CITE II (A) UNIVERSIDAD.

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Presentación del tema: "MEDIDA DE ALTURAS CON GPS (medida sobre el nivel del mar) V. Corchete* Departamento de Física Aplicada Escuela Politécnica Superior – CITE II (A) UNIVERSIDAD."— Transcripción de la presentación:

1 MEDIDA DE ALTURAS CON GPS (medida sobre el nivel del mar) V. Corchete* Departamento de Física Aplicada Escuela Politécnica Superior – CITE II (A) UNIVERSIDAD DE ALMERÍA ALMERIA * Problema. Con GPS medimos la altura h sobre el elipsoide de referencia no la altura H sobre el nivel del mar (Figura 1). Solución. Si conocemos el valor de N (la altura del nivel mar medida sobre el elipsoide de referencia) podemos calcular H como: H = h GPS - N Para obtener el valor de N usamos un modelo de geoide, pues ese modelo es justo la medida del nivel del mar sobre el elipsoide de referencia (Figuras 2 y 3). Así, un programa de ordenador calcula el valor de N, pudiendo entonces obtener H con sólo efectuar la resta anterior. MODELOS DE GEOIDE PARA EL ÁREA IBÉRICA Fig. 2. Representación del valor de N medido en metros (http://airy.ual.es/www/nibgeo_spanish.htm). Fig. 3. Representación del valor de N medido en metros (http://airy.ual.es/www/sosgis_spanish.htm). elipsoide de referencia nivel del mar superficie de la Tierra h GPS H N Fig. 1. Relación que existe entre la altura medida sobre el elipsoide (h) y la altura medida sobre el nivel del mar (H).

2 The use of the gravimetric GEOid of TUNisia: GEOTUN V. Corchete* 1, C. Jallouli 2, M. Chourak 3,4 and N. Rebai 2 1 Higher Polytechnic School, University of Almeria, ALMERIA, Spain 2 Faculté des Sciences de Tunis, University Tunis El Manar, TUNIS, Tunisia 3 Faculté Polidisciplinaire d'Errachidia, University of Moulay Ismaïl, B.P. 509 BOUTALAMINE, Morocco 4 NASG (North Africa Seismological Group) *Corresponding author: Fax ; AECI Acknowledgements. The authors are grateful to the National Geophysical Data Center (NGDC), the Bureau Gravimetrique International (BGI) and the United States Geological Survey (USGS); who have provided the data used in this study. NGDC and USGS have supplied the elevation data required to compute the necessary terrain corrections, through the databases: ETOPO2 and SRTM 90M (available by FTP internet protocol). The Agency of International Cooperation (AECI, Spain) supported this research partially, through the project A/5830/06. The relation between orthometric height (H) and ellipsoidal (h) is the undulation of the geoid (N): H = h - N Ellipsoid H h NANA A B C H A = h A N A H B = h B N B H BA = h BA N BA NBNB N BA = B – N A 0 H BA h BA The use of the GPS for levelling requires a geoid model to get orthometric heights from ellipsoidal heights. Surface of the Earth Geoid Surface of the Earth GEOid model for TUNisia: GEOTUN

3 The first high-resolution gravimetric GEOid for TUNisia: GEOTUN V. Corchete* 1, C. Jallouli 2, M. Chourak 3,4 and N. Rebai 2 1 Higher Polytechnic School, University of Almeria, ALMERIA, Spain 2 Faculté des Sciences de Tunis, University Tunis El Manar, TUNIS, Tunisia 3 Faculté Polidisciplinaire d'Errachidia, University of Moulay Ismaïl, B.P. 509 BOUTALAMINE, Morocco 4 NASG (North Africa Seismological Group) *Corresponding author: Fax AECI Figure 1. Gravity data. Figure 2. EIGEN-GL04C geoid. Figure 3. Digital Terrain Model (DTM). Acknowledgements. The authors are grateful to the National Geophysical Data Center (NGDC), the Bureau Gravimetrique International (BGI) and the United States Geological Survey (USGS); who have provided the data used in this study. NGDC and USGS have supplied the elevation data required to compute the necessary terrain corrections, through the databases: ETOPO2 and SRTM 90M (available by FTP internet protocol). The Agency of International Cooperation (AECI, Spain) supported this research partially, through the project A/5830/06. REFERENCES Corchete, V., M. Chourak and D. Khattach. The high-resolution gravimetric geoid of Iberia: IGG2005. Geophys. J. Int., 162, 676–684, Förste, C., F. Flechtner, R. Schmidt, R. König, U. Meyer, R. Stubenvoll, M. Rothacher, F. Barthelmes, H. Neumayer, R. Biancale, S. Bruinsma, J.-M. Lemoine and S. Loyer. A mean global gravity field model from the combination of satellite mission and altimetry/gravimetry surface data: EIGEN-GL04C. Geophysical Research Abstracts, Vol. 8, 03462, Figure 6. Gravimetric GEOid of TUNisia (GEOTUN). Figure 4. Terrain correction.Figure 5. Indirect effect. Computation of the geoid We have followed the computation method detailed by Corchete et al. (2005) for the calculation of the gravimetric geoid shown in Figure 6. Following this method, a complete data set consisting of: free-air gravity anomalies, a geopotential model and a high precision DTM; is necessary. The gravity data used have been 8628 points, distributed over the study area as it is shown in the Figure 1. The EIGEN-GL04C model (Förste et al., 2006) represents a major advance in the modelling of the Earths gravity and geoid (Figure 2). Therefore, this geopotential model has been considered in this study. Any gravimetric geoid computation must use anomalies that have been reduced to the geoid. This involves the computation of the terrain correction (Figure 4) and the indirect effect (Figure 5) on the geoid, which are computed from a DTM (Figure 3). This DTM is based on the SRTM (Shuttler Radar Topography Mission) and ETOPO2.

4 Bouguer anomaly map of the Moroccan area V. Corchete* 1, M. Chourak 2,3 and D. Khattach 4 1 Higher Polytechnic School, University of Almeria, ALMERIA, Spain 2 Faculté Polidisciplinaire d'Errachidia, University of Moulay Ismaïl, B.P. 509 BOUTALAMINE, Morocco 3 NASG (North Africa Seismological Group) 4 Faculté des Sciences, University of Mohamed I, OUJDA, Morocco *Corresponding author: Fax ; AECI Figure 1. Gravity data. Figure 5. Bouguer anomaly map of the Moroccan area. Acknowledgements. The authors are grateful to the National Geophysical Data Center (NGDC), the Bureau Gravimetrique International (BGI) and the United States Geological Survey (USGS); who have provided the data used in this study. NGDC and USGS have supplied the elevation data required to compute the necessary terrain corrections, through the databases: ETOPO2 and SRTM 90M (available by FTP internet protocol). The Agency of International Cooperation (AECI, Spain) supported this research partially, through the project 4/04/P/E. REFERENCES Corchete, V., M. Chourak and D. Khattach. The high-resolution gravimetric geoid of Iberia: IGG2005. Geophys. J. Int., 162, 676–684, Corchete, V., M. Chourak, D. Khattach and E. H. Benaim. The high-resolution gravimetric geoid of Morocco: MORGEO. Journal of African Earth Sciences, 48, , Figure 2. Digital terrain model (DTM). Computation of the Bouguer anomalies Since the gravity data set consisting of point data anomalies distributed randomly (Figure 1), we need to interpolate these data to obtain a regular data grid (Corchete et al. 2007). Before the interpolation, the short-wave effects that appear in the gravity anomaly field, associated to the short-wave topography and bathymetry, must be corrected (Corchete et al., 2005). Thus, we can compute a regular grid of free-air gravity data, as it is shown in Figure 3. When we have obtained the free-air gravity anomalies gridded, we can compute the Bouguer complete anomalies, as it shown in Figure 5, considering the terrain correction (Figure 4) previously obtained from a DTM of the study area (Figure 2). This DTM is based on the SRTM (Shuttler Radar Topography Mission) and ETOPO2. Figure 3. Free-air anomaly map. Figure 4. Terrain correction.


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