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Magnetic and gravity anomalies in the Americas
Abstract
The cleaning and magnetic tape storage of spherical Earth processing programs are reported. These programs include: NVERTSM which inverts total or vector magnetic anomaly data on a distribution of point dipoles in spherical coordinates; SMFLD which utilizes output from NVERTSM to compute total or vector magnetic anomaly fields for a distribution of point dipoles in spherical coordinates; NVERTG; and GFLD. Abstracts are presented for papers dealing with the mapping and modeling of magnetic and gravity anomalies, and with the verification of crustal components in satellite data.
... • prisms (Everest 1830, Nagy 1966a, Nagy 1966b, Hjelt 1974, Ketelaar 1976, Forsberg 1984, Ketelaar 1987,Werner and Scheeres 1996, Tsoulis 1998, Tsoulis 1999, Nagy et al. 2000, Smith 2000, Tsoulis 2001, Heck and Seitz 2007, Tsoulis et al. 2009), • line-masses (Tsoulis 1999, Wild-Pfeiffer 2008, • point-masses (Tsoulis 1999, Heck and Seitz 2007, Wild-Pfeiffer 2008, Reguzzoni et al. 2013), • layer-masses (Tsoulis 1999, Tsoulis et al. 2003, Wild-Pfeiffer 2008, • Gauss-Legendre quadrature (Hwang et al. 2003, Asgharzadeh et al. 2007, Roussel et al. 2015, Uieda et al. 2016), • polyhedral bodies (Coggon 1976, Pohánka 1988, Tsoulis et al. 2003, Tsoulis 2012, D'Urso 2013, D'Urso 2014, Werner 2017), • tesseroids (Ku 1977, Heck and Seitz 2007, Wild-Pfeiffer 2008, Tsoulis et al. 2009, Li et al. 2011, Grombein et al. 2013, Hirt and Kuhn 2014, Uieda et al. 2016), • tetrahedra (Casenave et al. 2016), • prisms and tesseroids combination (Tsoulis et al. 2009, Shen andHan 2013), • prisms and polyhedrons combination (Chai and Hinze 1988, Garcia-Abdeslem 2005, D'Urso 2015. Some of the available routines for calculation of topographic effects include: TC (Forsberg 1984, Tscherning 1994, Terrain (Ma and Watts 1994), INTLOG5A (Smith 2000), TcLight (Biagi and Sanso 2001), TCQ (Hwang et al. 2003), FA2BOUG (Fullea et al. 2008), GTeC (Cella 2015), GTE , Capponi et al. 2018, and Tesseroids (Uieda et al. 2010, Uieda et al. 2016). ...
******* THESIS+PRESENTATION (complete pdf versions below).********
One of the ultimate goals in geodesy, a 1 cm geoid model, is still unreachable for most of the areas worldwide. Several theoretical, methodological, numerical and data problems will have to be resolved in order to achieve it. The main motivation of this research is in making methodological and empirical contribution towards resolving some of the open problems in the regional gravity field and geoid modeling.
Topographic and density effects which affect short and very-short wavelengths of the gravity field have been traditionally modelled using the constant parameters of the Earth’s crust. As such parameters are only an approximation, this has been a limitation in more accurate filtering and reduction of the gravity data. Therefore, a methodology was developed which allows inclusion of surface and three dimensional crustal models in all steps of geoid determination. Prior to this, surface crustal density models were developed based on the inversion methods according to Pratt-Hayford, Airy-Heiskanen, and Parasnis-Nettleton. Additionally, three-dimensional crustal models EPcrust and CRUST1.0 were included in the computations. As a result of including crustal density models, the accuracy of developed gravimetric geoid models was improved from 1 to 3 cm.
The second major focus of research was related to the problem of the diversity of possible geoid computation methods and dozens of ways to perform reduction of the gravity field. The comparison of two widely used geoid modelling approaches was performed: Royal Institute of Technology (KTH) and Remove-Compute-Restore (RCR). Furthermore, compute step in RCR approach may be performed using several spectral and spatial methods. Therefore, different geoid computation methods were compared, including analytic Stokes integration using different deterministic modifications of the Stokes’ kernels, planar and spherical Fast Fourier Technique (FFT), flat-Earth and 3D least squares collocation (LSC). KTH approach, being a relatively straightforward geoid modelling approach compared to the RCR, was used for the analysis of the influence of all input models and parameters on the accuracy computed geoid models. From the large number of computed geoid solutions, two final gravimetric and hybrid geoid models for Croatia were selected HRG2018-RCR and HRG2018-KTH having standard deviation of ±3.0 cm and ±3.5 cm. The accuracy of geoid models was validated on GNSS/levelling points with seven parametric models using a unique cross-validation fitting methodology. Few other aspects of regional gravity field modeling were researched: i) investigation of the influence of input models and parameters in obtaining residual gravity field used in the RCR approach, ii) validation of the accuracy of global geopotential models, and iii) validation of gridding methods for several types of gravity anomalies.
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