Relevant bibliographies by topics / GeoIP / Dissertations / Theses
To see the other types of publications on this topic, follow the link: GeoIP.

Dissertations / Theses on the topic 'GeoIP'

Author: Grafiati
Published: 4 June 2021
Last updated: 6 February 2022

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the top 50 dissertations / theses for your research on the topic 'GeoIP.'

Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.

You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.

Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.

1

Smrčka, Lukáš. "Registrační databáze IP adres." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-220537.

Full text
Abstract:
This thesis is focused on finding the physical location of stations by the passive geolocation techniques, particularly using the registration database of IP addresses. The first two part are focused on a theoretical analysis of this problem, the next two parts of this thesis deal with the solution of this problem and discussion of the results.
APA, Harvard, Vancouver, ISO, and other styles
2

Dvořák, Filip. "Využití znalosti topologie páteřních sítí pro určování fyzické polohy stanic v síti Internet." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219422.

Full text
Abstract:
The thesis discusses about modern geolocation methods and it describes the basic principles of their work. The work is divided into 2 parts - the theoretical one and the practical one. The first part of the thesis is focused on the description of these methods and on the explanation of its basic concepts which are used for determining of the physical position of the station according to its IP address. The second more extensive part of the work focuses on the description of the realization of algorithm in the Octant method in the programming language of Java and its use in the experimental net of PlanetLab. One important thing is to create a set of reference points and targets, which are necessary for the testing of the whole algorithm of the Octant Method. The results of estimated accuracy of target location obtained by the Octant method and their comparison with the results obtained by active methods of CBG, SOI and with the passive method of GeoIP are listed at the end of this work.
APA, Harvard, Vancouver, ISO, and other styles
3

Boener, Joseph H. "Monterey Bay geoid." Thesis, Monterey, California. Naval Postgraduate School, 1994. http://hdl.handle.net/10945/30875.

Full text
Abstract:
A high resolution local geoid was calculated for the Monterey Bay, CA using local gravimetry data, digital elevation data and The Ohio State University OSU91A global geopotential model. The theoretical accuracy of the calculated local geoid is 3.5 cm or better over 5 km. Local gravity data came from three sources: 1,549 land observations from the Defense Mapping Agency, 179 bottom gravity observations from two Naval Postgraduate School gravity surveys of Monterey Bay and 17,098 National Geodetic Survey land and ship gravity observations from the National Geophysical Data Center's Gravity CD-ROM. Digital terrain elevation data came from the Rocky Mountain Communication Inc. 3 Arc Second Digital Terrain Elevation CD-ROM. A GPS sea surface topography experiment conducted in October, 1993, had indicated an anomalous sea slope across the bay from Santa Cruz, California to Monterey, California. Comparisons between the calculated local geoid and the regional geoid for The United States, the National Geodetic Survey's GEOID93 indicated a possible explanation for the anomalous sea slope being a local slope in the geoid. Geoid, Monterey Bay, Sea surface.
APA, Harvard, Vancouver, ISO, and other styles
4

Li, Yecai. "Airborne gravimetry for geoid determination." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0018/NQ54797.pdf.

Full text
APA, Harvard, Vancouver, ISO, and other styles
5

Gerrard, Sara Margaret Elizabeth. "The geoid, GPS and levelling." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278288.

Full text
APA, Harvard, Vancouver, ISO, and other styles
6

Lerke, Otto. "GRACE-Eismassenbilanz." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-33282.

Full text
APA, Harvard, Vancouver, ISO, and other styles
7

Twigg, D. R. "Finite element interpolation of geoid heights." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355479.

Full text
APA, Harvard, Vancouver, ISO, and other styles
8

Garcia, Ramon V. "Local geoid determination from GRACE mission /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486398195325232.

Full text
APA, Harvard, Vancouver, ISO, and other styles
9

Ellmann, Artu. "The geoid for the Baltic countries determined by the least squares modification of Stokes´formula." Doctoral thesis, KTH, Infrastructure, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3744.

Full text
Abstract:

Precise knowledge of the geoid contributes to the studies ofthe Earth’s interior, the long-term geophysical processesand to oceanography. An accurate regional geoid model, inparticular, enables the user in many cases to replace thetraditional height determination techniques by faster and morecost-effective GPS-levelling.

In regional gravimetric geoid determination, it has becomecustomary to utilize the modified Stokes formula, whichcombines local terrestrial data with a global geopotentialmodel. The Dissertation is devoted to the determination of ahighresolution geoid model for the three Baltic countries–Estonia, Latvia and Lithuania. Six differentdeterministic and stochastic modification methods are tested.These are: Wong and Gore (1969), Vincent and Marsh (1974),Vaníèek and Kleusberg (1987) and the biased, unbiasedand optimum least squares modifications by Sjöberg (1984b,1991, 2003d). Three former methods employ originally theresidual anomaly in Stokes’integral. For the sake ofcomparison these methods are expressed such that the fullgravity anomaly is utilised in all the six methods.

The contribution of different error sources for geoidmodelling is studied by means of the expected global meansquare error (MSE). The least squares methods attempt tominimise all relevant error sources in geoid modelling byspecially determined modification parameters. Part of thepresent study contributes to some important computationalaspects of the least squares parameters sn.

This study employs the new geopotential model GGM01s, whichis compiled from data of the GRACE twin-satellites. Three sets(one from each country) of GPSlevelling points were used for anindependent evaluation of computed geoid models. Generally, thepost-fit residuals from the least squares modifications areslightly smaller (up to 1 cm) than the respective values ofdeterministic methods. This could indicate that the efforts putinto minimization of the global MSE have been advantageous.

The geoid model computed by the unbiased LS modificationprovides the“best”post-fit statistics and it isthus preferred as the final representation of the joint Balticgeoid. The modification parameters of this model are calculatedfrom the following initial conditions: (1) upper limit of theGGM01s and the modification degree of Stokes’function areboth set to 67, (2) terrestrial anomaly error variance andcorrelation length are set to 1 mGal2 and 0.1°,respectively, (3) integration cap size is 2°. Thisapproximate geoid model is supplemented by separately computedadditive corrections (the combined topographic and atmosphericeffects and ellipsoidal correction), which completes the geoidmodelling procedures. The new geoid model for the Balticcountries is named BALTgeoid-04. The RMS of the GPS-levellingpost-fit residuals are as follows: 5.3 cm for the joint Balticgeoid model and 2.8, 5.6 and 4.2 cm for Estonia, Latvia andLithuania, respectively. This fit indicates the suitability ofthe new geoid model for many practical applications.

Key words: geoid:Stokes’formula, deterministicand stochastic modifications, least squares, additivecorrections, GRACE, Baltic.

APA, Harvard, Vancouver, ISO, and other styles
10

Azmoudeh-Ardalan, Alireza. "High resolution regional geoid computation in the world geodetic datum 2000 based upon collocation of linearized observational functionals of the type GPS, gravity potential and gravity intensity /." [S.l.] : Universität Stuttgart , Fakultät Bauingenieur- und Vermessungswesen , Geodätisches Institut, 1999. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8733302.

Full text
APA, Harvard, Vancouver, ISO, and other styles
11

Eis, Pavel. "Datová sada pro klasifikaci síťových zařízení pomocí strojového učení." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2021. http://www.nusl.cz/ntk/nusl-445543.

Full text
Abstract:
Automatic classification of devices in computer network can be used for detection of anomalies in a network and also it enables application of security policies per device type. The key to creating a device classifier is a quality data set, the public availability of which is low and the creation of a new data set is difficult. The aim of this work is to create a tool, that will enable automated annotation of the data set of network devices and to create a classifier of network devices that uses only basic data from network flows. The result of this work is a modular tool providing automated annotation of network devices using system ADiCT of Cesnet's association, search engines Shodan and Censys, information from PassiveDNS, TOR, WhoIs, geolocation database and information from blacklists. Based on the annotated data set are created several classifiers that classify network devices according to the services they use. The results of the work not only significantly simplify the process of creating new data sets of network devices, but also show a non-invasive approach to the classification of network devices.
APA, Harvard, Vancouver, ISO, and other styles
12

Vajda, Peter. "The truncated geoid and the gravimetric inverse problem." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1995. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ46304.pdf.

Full text
APA, Harvard, Vancouver, ISO, and other styles
13

Craig, C. H. "Numerical modelling of mantle convection and the geoid." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372867.

Full text
APA, Harvard, Vancouver, ISO, and other styles
14

Najafi, Alamdari Mehdi. "Contributions towards the computation of a precise regional geoid." Thesis, University of New Brunswick, 1996. http://hdl.handle.net/1882/375.

Full text
APA, Harvard, Vancouver, ISO, and other styles
15

Najafi, Alamdari Mehdi. "Contributions towards the computation of a precise regional geoid." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23868.pdf.

Full text
APA, Harvard, Vancouver, ISO, and other styles
16

Serpas, Juan Gilberto. "Local and regional geoid determination from vector airborne gravimetry." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1066757143.

Full text
APA, Harvard, Vancouver, ISO, and other styles
17

Amod, Ameer. "The use of spectral methods in Quasi-geoid modelling." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/4990.

Full text
APA, Harvard, Vancouver, ISO, and other styles
18

Holst, Christine. "Bestimmung des Potentialwertes für das finnische Höhendatum unter Berücksichtigung der neuen Satelliten-Schwerefeldmodelle." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11482106.

Full text
APA, Harvard, Vancouver, ISO, and other styles
19

Nunes, Vagner Conceição. "Testes sobre a eficiência do modelo do geopotencial EGM2008 na cidade de Porto Alegre." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/26992.

Full text
Abstract:
Este estudo apresenta o teste da eficiência do Earth Global Model 2008 (EGM2008) na geração de um modelo geoidal local, através da compatiblização com a ondulação obtida por posicionamento GPS (Global Positioning System) em 63 Referências de Nível (RN’s) localizadas no município de Porto Alegre, Rio Grande do Sul. O objetivo geral da dissertação foi analisar a exatidão do modelo geoidal gerado a partir dos coeficientes do modelo geopotencial EGM2008 para nivelamento por GPS no município de Porto Alegre e os objetivos específicos foram: a avaliação do modelo na região de Porto Alegre, a comparação das ondulações geoidais do EGM2008 (NEGM2008) com as ondulações geoidais em 63 RN’s (NGPS), o ajustamento da componente sistemática do geoide que é a diferença entre NEGM2008 e NGPS e a geração do modelo geoidal local compatibilizado para Porto Alegre. O método adotado apresenta as seguintes etapas: cálculo das ondulações geoidais nas RN’s; eliminação de erros grosseiros; geração do modelo geoidal através dos dados do EGM2008 com resolução de 7” de arco; cálculo da componente sistemática do geoide; ajustamento da componente sistemática através de transformação por polinômio de 2° grau com seis parâmetros pelo Método dos Mínimos Quadrados (MMQ). Os resultados obtidos foram: os parâmetros que compatibilizam o modelo geoidal global com o local e modelo geoidal local compatibilizado no formato raster, contendo as ondulações geoidais para todo o município. O novo modelo apresentou erro médio de 1,9 cm e desvio padrão de 7,2 cm. Os resultados da dissertação confirmam que é possível reduzir o erro associado ao modelo global através dos procedimentos adotados. Dessa maneira, conclui que o método utilizado reduziu o valor médio da componente sistemática de 15,4 cm para 1,9 cm após o ajustamento.
This study presents the Earth Global Model 2008’s (EGM2008) efficiency test on the conception of a local geoid model. The results were acquired through the undulation compatibility obtained by GPS (Global Positioning System) in 63 Bench Mark (BM) located in Porto Alegre, Rio Grande do Sul state, Brazil. The aim of this research was to analyze the accuracy of the geoid model generated from the geopotential model EGM2008’s coefficients to GPS leveling in Porto Alegre. The specific goals were the evaluation of the model in Porto Alegre region’s, the comparison between the EGM2008 (NEGM2008) geoid undulations and the geoid undulations in 63 BM (NGPS), and the adjustment of geoid’s systematic component, that is the difference between NEGM2008 and NGPS and the local geoid model’s conception to Porto Alegre. The method used presents the following steps: geoid undulation on RN’s’s computation; elimination of gross errors; geoid model’s conception through EGM2008’s data with resolution of 7” of arch; geoid’s systematic component computation; adjustment of the systematic component through transformation of 2nd degree polynomial with six parameters by the method of Least Squares. The results were: the parameters that make the models global and local compatible, and local geoid model compatible in raster format, containing the geoid undulations for the entire municipality. The new model showed 1.9 of mean error and 7.2 cm of standard deviation. Through the procedures adopted, the dissertation results’ confirm that it is possible to reduce the error associated of the the global model. Therefore, the conclusion is that the method used reduced the mean error of the systematic component from 15,4 cm to 1.9 cm, after the adjustment.
APA, Harvard, Vancouver, ISO, and other styles
20

Thomas, P. L. "Satellite altimetry and the geoid over the north-east Atlantic." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371291.

Full text
APA, Harvard, Vancouver, ISO, and other styles
21

Wan, Mohd Akib Wan Abdul Aziz. "A preliminary determination of a gravimetric geoid in Peninsular Malaysia." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283665.

Full text
APA, Harvard, Vancouver, ISO, and other styles
22

Nyamangunda, Patrick. "Towards a 10cm local gravimetric geoid for Zimbabwe using FFT." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301119.

Full text
APA, Harvard, Vancouver, ISO, and other styles
23

Somieski, Anna Eve. "Astrogeodetic geoid and isostatic considerations in the North Aegean Sea, Greece /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17790.

Full text
APA, Harvard, Vancouver, ISO, and other styles
24

Kamarudin, Md Nor. "Local geoid determination from a combination of gravity and GPS data." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363535.

Full text
APA, Harvard, Vancouver, ISO, and other styles
25

Benevenuto, Junior Pedro. "Geoia e ecologia da Leishmaniose Tegumentar no Estado do Espírito Santo." reponame:Repositório Institucional da FIOCRUZ, 2000. https://www.arca.fiocruz.br/handle/icict/4939.

Full text
Abstract:
Made available in DSpace on 2012-09-06T01:11:40Z (GMT). No. of bitstreams: 2 license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) 173.pdf: 2208383 bytes, checksum: 635f306a24f3f4622676b8f32494f657 (MD5) Previous issue date: 2000
A Leishmaniose Tegumentar Americana (LTA) é uma doença infecciosa de evoluçao crônica, causada por protozoários do gênero Leishmania, que pode acometer pele e mucosas do nariz, boca, faringe e laringe, isoladamente ou nao. E uma zoonose transmitida por insetos, genericamente conhecidos como flebotomíneos, popularmente chamados de mosquito palha, cangalhinha, tatuquira, etc. A Organizaçao Mundial da Saúde (OMS) inclui a LTA entre as seis doenças infecciosas e parasitárias prioritárias para açoes de controle, pelo seu potencial epidêmico. Com o objetivo de tentar melhor compreender a epidemiologia da Leishmaniose Tegumentar Americana no Estado do Espírito Santo, realizou-se um estudo do numero de casos acontecidos no período de 1989 a 1998 por município, utilizando-se Sistemas de Informaçao Geográfica-SIG. Foram calculadas as taxas de incidência por município, considerando os limites administrativos de 1991, tomando-se por base os dados como sao registrados pela Fundaçao Nacional de Saúde (Regional Espírito Santo) e a populaçao fornecida pelo IBGE. Foi feita a regularizaçao da série temporal através de Médias Móveis de 5 meses, para diminuir a flutuaçao dos dados, e feito também a modelagem da tendência através de polinômio de terceiro grau. Utilizando-se alguns tipos de análise, fizeram-se as projeçoes em mapas, ano a ano categorizando de acordo com os parâmetros utilizados pela FNS para classificar Taxas Baixas, Médias, Altas e Muito Altas e estudar o comportamento espacial da Leishmaniose Tegumentar Americana por município. Para análise espacial considerando o número de casos, as respectivas taxas de incidência e suas relaçoes com as variáveis ambientais, utilizou-se o SIG Arc-View, através de mapas coropléticos com sobreposiçao de camadas, além do software S-Plus para utilizar-se o Estimador de Kernel para alisamento dos dados no sentido de se determinar as "Areas Quentes" e verificar a intensidade do evento em relaçao a área estudada.
APA, Harvard, Vancouver, ISO, and other styles
26

Danila, Uliana. "Mold2012 : a new gravimetric quasigeoid model over Moldova." Licentiate thesis, KTH, Geodesi och geoinformatik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105755.

Full text
Abstract:
In order to be able to use the operational Moldavian GNSS Positioning System MOLDPOS efficiently for the determination of normal heights in surveying engineering, e.g. during the construction of a road, an accurate quasigeoid model is needed. The main goal of this thesis is to present a new gravimetric quasigeoid model for Moldova (Mold2012), which has been determined by applying the Least Squares Modification of Stokes’ formula with Additive corrections (LSMSA), also called the KTH method. Due to limited coverage of gravity data, the integration area is often limited to a small spherical cap around the computation point, which leads to a truncation error for geoid height. Molodensky et al. (1962) showed that the truncation error can be reduced by the modification of Stokes’ formula, where the measured gravity data are combined with the low-frequency component of the geoid from a Global Gravitational Model (GGM). The LSMSA technique combines the GGM and the terrestrial data in an optimum way. In order to find the most suitable modification approach or cap size it is necessary to compare the gravimetric height anomalies with the GPS/levelling derived height anomalies, and for this purpose we use a GPS/levelling dataset that consists of 1042 points with geodetic coordinates in the MOLDREF99 reference system and normal heights at the same points given in the height system Baltic 77. The magnitude of the additive corrections varies within an interval from -0.6 cm to -4.3 cm over the area of Moldova. The quasigeoid model which results from combining the ITG-Grace02s solution (with n = M = 170, ψ0 = 3° and σΔg = 10 mGal) and the solution obtained from the modified Stokes’ formula together with the additive correction gives the best fit for the GPS/levelling data with a standard deviation (STD) of ±7.8 cm. The evaluation of the computed gravimetric quasigeoid is performed by comparing the gravimetric height anomalies with the GPS/levelling derived height anomalies for 1042 points. However, the above heterogeneous data include outliers, and in order to find and eliminate these, a corrector surface model is used. This surface provides a connection to the local vertical when the GNSS technique is used. After the elimination of the suspicious outliers (170 points) according to a 2-RMS test, a new corrective surface was computed based on the remaining 872 GPS/levelling points, and the STD of residuals became ±4.9 cm. The STD value for the residuals according to the order of the levelling network for the Mold2012 fitted to the local vertical datum is 3.8 cm for the I-order, 4.3 cm for the II-order, 4.5 cm for the III-order and 5.0 cm for the IV-order levelling network. But the STD of the residuals for the 18 control points indicates a better result where the STD is 3.6 cm and RMS is 3.9 cm and the min and max value of residuals is -5.3 cm and 9.0 cm, respectively. As the STD of the differences in height anomaly are not just the standard error of the height anomalies (quasigeoid model), but it contains also the standard errors of GPS heights and of normal heights. Assuming that the latter STDs are 3 cm and 3.5 cm, respectively, the STD of Mold2012 is estimated to 1.7 cm.

QC 20121127

APA, Harvard, Vancouver, ISO, and other styles
27

Inerbayeva, (Shoganbekova) Daniya. "Determination of a gravimetric geoid model of Kazakhstan using the KTH-method." Thesis, KTH, Geoinformatik och Geodesi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-52284.

Full text
Abstract:
This study work deals with the determination of the gravimetric geoid model for Kazakhstan by using the KTH-method. A number of data sets were collected for this work, such as the gravity anomalies, high-resolution Digital Elevation Model (DEM), Global Geopotential Models (GGMs) and GPS/Levelling data. These data has been optimally combined through the KTH approach, developed at the Royal Institute of Technology (KTH) in Stockholm. According to this stochastic method, Stokes’ formula is being used with the original surface gravity anomaly, which combine with a GGM yields approximate geoid heights. The corrected geoid heights are then obtained by adding the topographic, downward continuation, atmospheric and ellipsoidal corrections to the approximate geoid heights. To compute the geoid model for Kazakhstan as accurately as possible with available data set different numerical tests have been performed: Choice of the best fit geopotential model in the computation area Investigations for the best choice of the initial condition for determination of the least-squares parameters Selection of the best parametric model for reducing the effect of the systematic error and data inconsistencies between computed geoid heights and GPS/Levelling heights.  Finally, 5'x5' Kazakh gravimetric geoid (KazGM2010) has been modelled.
APA, Harvard, Vancouver, ISO, and other styles
28

Nahavandchi, Hossein. "Precise gravimetric-GPS geoid determination with improved topographic corrections applied over Sweden." Doctoral thesis, KTH, Geodesy and Photogrammetry, 1998. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2726.

Full text
APA, Harvard, Vancouver, ISO, and other styles
29

Featherstone, William Edward. "A G.P.S. controlled gravimetric determination of the geoid of the British Isles." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306204.

Full text
APA, Harvard, Vancouver, ISO, and other styles
30

Agner, Mary Alexandra. "The effect of a low density residuum on geoid anomalies and topography." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/57762.

Full text
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998.
Includes bibliographical references (p. 27-28).
Recent seismological measurements of the Pacific oceanic structure have detected a positive correspondence between surface topography, seismic wave speed, and the geoid (gravitational potential). High seismic wave speed indicates cold material sinking, which pulls the surface downward. Thus, topographic lows are expected to correlate with seismic wave speed highs, contrary to the new seismic measurements. We propose models which include two segregated materials, representing the fertile upper mantle and the residue from crustal melting, in order to decouple the surface topography from subsurface convection and create a positive correlation between topography and wave speed. We add a low viscosity zone beneath the residue to enhance the density contribution to the geoid anomaly and ensure that its sign is in phase with that of the surface topography and wave speed. Our models produce surface topography and geoid anomalies comparable to the recent seismological measurements. These models offer constraints on the strength of the low viscosity zone as well as the density difference between the residue and the upper mantle.
by Mary Alexandra Agner.
S.M.
APA, Harvard, Vancouver, ISO, and other styles
31

Abdalla, Ahmed. "Determination of a gravimetric geoid model of Sudan using the KTH method." Thesis, KTH, Geodesi och satellitpositionering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199670.

Full text
Abstract:
The main objective of this study is to compute a new gravimetric geoid model of Sudan using the KTH method based on modification of Stokes’ formula for geoid determination. The modified Stokes’ formula combines regional terrestrial gravity with long-wavelength gravity information provided by the global gravitational model (GGM). The collected datasets for this study contained the terrestrial gravity measurements, digital elevation model (DEM), GPS/levelling data and four global gravitational Models (GGMs), (EGM96, EIGEN-GRACE02S, EIGEN-GL04C and GGM03S). The gravity data underwent cross validation technique for outliers detection, three gridding algorithms (Kriging, Inverse Distance Weighting and Nearest Neighbor) have been tested, thereafter the best interpolation approach has been chosen for gridding the refined gravity data. The GGMs contributions were evaluated with GPS/levelling data to choose the best one to be used in the combined formula. In this study three stochastic modification methods of Stokes’ formula (Optimum, Unbiased and Biased) were performed, hence an approximate geoid height was computed. Thereafter, some additive corrections (Topographic, Downward Continuation, Atmospheric and Ellipsoidal) were added to the approximated geoid height to get corrected geoid height. The new gravimetric geoid model (KTH-SDG08) has been determined over the whole country of Sudan at 5′ x 5′ grid for area ( 4 ). The optimum method provides the best agreement with GPS/levelling estimated to 29 cm while the agreement for the relative geoid heights to 0.493 ppm. A comparison has also been made between the new geoid model and a previous model, determined in 1991 and shows better accuracy. 􀁄 ≤φ ≤ 23􀁄 , 22􀁄 ≤ λ ≤ 38􀁄 Keywords: geoid model, KTH method, stochastic modification methods, modified Stokes’ formula, additive corrections.
APA, Harvard, Vancouver, ISO, and other styles
32

Kirby, Jonathan Frank. "The development and application of a new algorithm for ocean geoid recovery." Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/15179.

Full text
Abstract:
The thesis describes and tests a method to combine satellite measurements of the geoid height with shipboard and terrestrial measurements of the freeair gravity anomally using Fourier transform techniques. Fast Fourier transforms can process very large data sets quickly but require the data to be available on a complete and regular grid. New methods were devised that grid altimeter and marine gravity data, and which remove the long-wavelength errors associated with these measurements. Satellite altimeter data distributed along widely spaced groundtracks are differenced along track to reduce long-wavelength orbit errors, and any repeat track observations are averaged to reduce time-dependent oceanographic noise. The ascending and descending along-track slopes are then gridded separately, using a kernel designed to extrapolate the observations smoothly into the gaps between tracks, while retaining the high along-track resolution of the data. The spectral properties of the gridding operation, were analysed by calculation of a transfer function. In a development of Sandwell's method, the grids of along-track slopes are transformed using vector algebra to grid-easting and -northing deflections of the vertical. Vertical deflection grids from any number of satellite missions may now be combined, then converted using Fourier techniques to give a grid of the geoid height. This grid is easily converted to a grid of the freeair anomaly. The effect of datum errors in the shipboard gravity data is also reduced by processing not gravity but along-track gravity gradient. An incomplete grid of freeair gravity anomalies is generated from the observed along-track gravity slopes, constrained by, and improving the altimeter-derived freeair anomaly grid. Land gravity measurements are interpolated directly onto a separate grid as there is no similar long-wavelength error in the data. The combination algorithm performs a weighted superposition of the geoid height and freeair anomaly grids in an iterative process, until self-consistent. The algorithms were first tested on a simulated dataset, extracted from accurate, high-resolution and self-consistent geoid and freeair anomaly models of the British Isles and North Sea. The geometry of real altimeter tracks from an area of equal size in the North Atlantic were superimposed on the British geoid, and simulated readings interpolated.
APA, Harvard, Vancouver, ISO, and other styles
33

Esan, Olugbenga. "Spectral analysis of gravity field data in view of sub-decimeter geoid determination." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0015/MQ55259.pdf.

Full text
APA, Harvard, Vancouver, ISO, and other styles
34

Daras, IIias. "Determination of a gravimetric geoid model of Greece using the method of KTH." Thesis, KTH, Geodesi och satellitpositionering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199682.

Full text
Abstract:
The main purpose of this study is to compute a gravimetric geoid model of Greeceusing the least squares modification method developed at KTH. In regional gravimetricgeoid determination, the modified Stokes’s formula that combines local terrestrial datawith a global geopotential model is often used nowadays.In this study, the optimum modification of Stokes’s formula, introduced by ProfessorSjöberg, is employed so that the expected mean square error (MSE) of all possiblesolutions of the general geoid model is minimized. According to this stochasticmethod, the Stokes’s formula is being used with the original surface gravity anomalywhich combined with a GGM yields an approximate geoid height. The corrected geoidheight is then obtained by adding the topographic, downward continuation,atmospheric and ellipsoidal corrections to the approximate geoid height.The dataset used for the computations, consisted of terrestrial gravimetricmeasurements, a DEM model and GPS/Levelling data for the Greek region. Threeglobal geopotential models (EGM96, EIGEN-GRACE02S, EIGEN-GL04C) weretested for choosing the best GGM to be combined into the final solution. Regarding theevaluation and refinement of the terrestrial gravity measurements, the cross-validationtechnique has been used for detection of outliers.The new Greek gravimetric geoid model was evaluated with 18 GPS/Levelling pointsof the Greek geodetic network. The absolute agreement between the gravimetric andthe GPS/Levelling geoid height was estimated at 27 cm while the relative agreement at0.9 ppm. In a case of study the absolute accuracy of the model was estimated at 14 cm.The geoid model computed in this study was also compared with some previous Greekgeoid models, yielding better external accuracy than them.
APA, Harvard, Vancouver, ISO, and other styles
35

Guimarães, Gabriel do Nascimento. "A altimetria e o modelo geoidal no Estado de São Paulo." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3138/tde-20102010-170156/.

Full text
Abstract:
Esta dissertação tem como objetivo o estudo da altimetria e do modelo geoidal no Estado de São Paulo. Para isso, uma abordagem detalhada do Problema de Valor de Contorno da Geodésia foi realizada. Além disso, são apresentados conceitos relacionados ao sistema de altitudes e a determinação das ondulações geoidais. Uma investigação do movimento e deslocamento vertical da crosta terrestre por meio do processamento preciso por ponto de duas estações de monitoramento contínuo (Cananeia NEIA e Ubatuba UBAT), localizadas no litoral paulista, foi efetuada. Constatou-se uma similaridade nos resultados por meio da comparação com o processamento feito pelo IBGE. A comparação envolvendo o Nível Médio dos Mares de duas estações maregráficas com relação ao nivelamento advindo de Imbituba foi outro estudo executado, onde a diferença após algumas correções foi de 0,34 cm. Uma análise a partir de 199 estações GPS sobre nivelamento foi realizada para comparação da ondulação geoidal com as anomalias de altura. As anomalias foram calculadas a partir dos modelos do geopotencial (EIGEN-GL04, EIGEN-5C e EGM08 para diferentes valores de grau e ordem). Os modelos que apresentaram melhor consistência com as estações GPS sobre nivelamento foram o EIGEN-GL04C e EIGEN-5C grau e ordem 360 e o EGM08 grau e ordem 360 e 2160. O modelo geoidal do Estado de São Paulo foi gerado para um modelo digital de 5. Utilizou-se a integral modificada de Stokes a partir do pacote computacional canadense SHGEO para o cálculo da componente de curto comprimento de onda. Foram empregados dados gravimétricos já existentes e dados advindos dos trabalhos de campo referentes ao Projeto Temático da FAPESP. No cálculo da componente de médio e longo comprimento de onda foi utilizado o modelo do geopotencial EGM08 (grau e ordem 150). A comparação com os dados GPS sobre nivelamento apresentou média de -0,22 m e RMSD 0,21 m. A escolha do Estado de São Paulo está relacionada à grande quantidade de trabalhos geodésicos e atividades na área da engenharia e que necessitam da utilização de um sistema altimétrico. Além disso, a grande quantidade de dados gravimétricos e de estações GPS/RN é mais uma justificativa para a realização do trabalho no Estado.
The investigation of the altimetry and the geoid model in São Paulo state is the aim of this dissertation. A detailed study concerning the Geodetic Boundary Value Problem was carried out. Moreover, the concepts related to the height system are presented. The analysis of the crust vertical displacement involving two continuous monitoring GPS stations (Cananeia NEIA and Ubatuba UBAT) in the coast of the state was performed. It was detected similar results between the comparison involved IBGE processing. A comparison involving the mean sea level of two tide gauge stations with respect to levelling from Imbituba was carried out. After some corrections the difference found was 0.34 m. A comparison between height anomalies by the Global Geopotential Models (EIGEN-GL04, EIGEN-5C and EGM08 for different degree and order) and 199 GPS observations on Bench Marks of the spirit leveling network was performed. The Global Geopotential Models that presented consistency with GPS on Bench Marks were: EIGEN-GL04C and EIGEN- 5C degree and order 360 and EGM08 degree and order 2160. São Paulo state geoid model was computed in 5 digital model. The modified Stokes integral by the Canadian package SHGEO to compute the short wavelength component was used, from Helmert gravity anomalies derived. Existing gravity data and data from FAPESP Thematic Project was processed. EGM08 model was used as a reference field restricted to degree and order 150 to obtain the long and medium wavelength components. The comparison with GPS on Bench Marks presented mean -0.22 m and RMSD 0.21 m. The reason for the choice of São Paulo state is that there are a lot of geodetic activities and important engineering works that require the use of a height system. Furthermore, there are a lot of gravimetric and GPS/BM data all around the state.
APA, Harvard, Vancouver, ISO, and other styles
36

Berntsson, Jenny. "A study on the quality of the NKG2015 geoid model over the Nordic countries." Thesis, Högskolan Väst, Avdelningen för Matematik, Data- och Lantmäteriteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-13960.

Full text
Abstract:
Geoidmodellen NKG2015 (Nordiska kommissionen för geodesi) är den senaste geoidmodellen över Norden. Det har inte publicerats någon forskning om kvaliteten på den här nya modellen, därför kan den här studien bidra till forskningen inom ämnet. Det är viktigt att vara medveten om begränsningarna och kvaliteten på den geoidmodell som används vid mätning av höjder. Om kvaliteten på geoidmodellen inte är känd så kommer kvaliteten på höjdmätningarna inte heller att vara känd. Detta kan skapa problem när mätningarna används i projekt där precision är viktigt. För att undersöka kvaliteten på geoidmodellen NKG2015 har geoidhöjderna beräknade från modellen jämförts med geoidhöjder som fås från mätning med metoden GNSS (Global Navigation Satellite Systems) /avvägning vid samma punkter. Slutningsfelet mellan geoidhöjderna från geoidmodellen och geoidhöjderna från mätningarna har analyserats med statistiska metoder. Slutningsfelens normalitet testas och analysen utförs på ofiltrerad data samt data som filtrerats med två olika konfidensintervall, 95% och 99,7%. Detta för att filtrera bort eventuella avvikande värden. Eventuella trender i datan jämnas ut med en metod baserad på minsta kvadratmetoden. Studiens resultat visar att filtrering av slutningsfelen generellt gör datan mer normalfördelad, men så är inte fallet för alla länder. I de flesta fall förbättras normaliteten även genom att jämna ut trender i datan. I processen med att jämna ut trender används en korrigerande yta med ett specificerat antal parametrar. Topografin i varje land spelar en stor roll när beslut ska fattas om hur många parametrar som behövs i den korrigerande ytan. Länder med höga berg och stora höjdskillnader så som Norge har en större osäkerhet i datan och kräver fler parametrar i den korrigerande ytan. Danmark är ett land med relativ platt topografi och behöver inte lika många parametrar i den korrigerande ytan som Norge för att effektivt jämna ut trender. Det finns givna värden på felen för datan som är uppmätt med GNSS/avvägning, dessa fel stämmer generellt inte överens med slutningsfelen. För Finland är det givna felet för GNSS/avvägning större än det borde vara medan felen för GNSS/avvägning i de andra länderna är något mindre än vad slutningsfelen antyder. De givna, uppskattade felen för geoidmodellen NKG2015 är 10 mm för Sverige och Danmark, 22 mm för Norge och 12 mm för Finland. Dessa fel är rimliga men stämmer inte helt överens med de givna felen för GNSS/avvägning i relation till slutningsfelen. Under antagandet att de givna felen för GNSS/avvägning är korrekta kan följande konfidensintervall uppskattas för geoidfelen; 06,5mm för Sverige, 1,8-5,2mm för Danmark, 14,8-17,7mm för Norge och 0-0mm för Finland.
The NKG2015 (Nordic Geodetic Commission) geoid model is the most recent official geoid model over the Nordic countries. There has been no previous research published on the quality of this model, therefore, this study may be a valuable contribution to the research in this area. It is important to be aware of the limitations and quality of the geoid model used when measuring heights. If the quality of the geoid is not known, the quality of the measured heights will also be uncertain. This might cause problems when the measured heights are used in projects where great precision is vital. Measured GNSS (Global Navigation Satellite Systems)/levelling data has been compared to the computed geoid heights from the NKG2015 geoid model at the corresponding points to investigate the quality of this model. The misclosures between the geoid height, obtained from the GNSS/levelling data and the geoid heights from the NKG2015 geoid model have been analysed by statistical methods. The normality of the misclosures is tested, and the analysis is performed on unfiltered and filtered misclosures with confidence intervals (CIs) of 95% and 99.7% to remove probable outliers. Trends in the misclosures are removed with a least-squares detrending method. The result of the study shows that filtering the misclosures generally makes them more normally distributed, but this is not the case for all countries. Detrending the misclosures improves the normality in most cases. In this process, a corrective surface with a specified number of parameters is fitted to the misclosures to remove trends. The topography of each country is very important when deciding which corrective surface that should be used in the detrending process. Countries with rough topography such as Norway has greater uncertainty in its heights and needs a corrective surface with more parameters than flatter countries such as Denmark. There are some estimates for the errors for the GNSS/levelling data which are not all in agreement with the misclosures. The GNSS/levelling error in Finland is greater than it should be. The given, estimated errors of the NKG2015 geoid model are 10 mm for Sweden and Denmark, 22 mm for Norway and 12 mm for Finland. These errors are reasonable, but not in perfect agreement with the given errors of the GNSS/levelling measurements in relation to the misclosures. Based on the assumption that the GNSS/levelling errors are correct, confidence intervals of the geoid error can be estimated. These estimated intervals are 0-6.5mm for Sweden, 1.8-5.2mm for Denmark, 14.8-17.7mm for Norway and 0-0mm for Finland. The confidence interval for Finland is not realistic because it is based on the assumption that the GNSS/levelling error is correct.
APA, Harvard, Vancouver, ISO, and other styles
37

Guimarães, Gabriel do Nascimento. "A geoid model in the state of São Paulo: an attempt for the evaluation of different methodologies." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3138/tde-30072013-234021/.

Full text
Abstract:
The purpose of this thesis is to compute and to evaluate the geoid model in the State of São Paulo from two methodologies (Stokes integral through the Fast Fourier Transform - FFT and Least Squares Collocation LSC). Another objective of this study is to verify the potentiality of GOCE-based. Therefore, a brief study about mathematical foundations and fundamentals of Physical Geodesy is carried out. Some features of the Global Geopotential Models (GGMs) are discussed, as well as an overview of the new gravimetric missions. A special attention is given to GOCE mission. The theory related to Stokes integral and Least Squares Collocation is also discussed in this work. The spectral decomposition was employed in the geoid models computation and the long wavelength component was represented by EGM2008 up to degree and order 150 and 360 and GOCE-based models up to 150. The models were compared in terms of geoid height residual and absolute and relative comparisons from GPS/leveling and the results show consistency between them. Also, a comparison in the mountain regions was carried out to verify the methodologies behavior in this area; the results showed that LSC is less consistent than FFT. Regarding GOCE-based models, 13 were tested, besides EGM2008. The evaluation was performed in terms of geoid height comparison obtained by GGMs over GPS/leveling and in terms of gravity disturbance. The evaluation shows that DIR _R3 and TIM_R3 presented more compatible results. The reason for the choice of São Paulo state is that there are a lot of geodetic activities and important engineering works that require the use of a height system. Furthermore, there are a lot of gravity and GPS/leveling data all around the state.
Esta tese tem como propósito o cálculo e a avaliação do modelo geoidal no Estado de São Paulo a partir da aplicação de duas metodologias (integral de Stokes por meio da Transformada Rápida de Fourier FFT e a colocação por mínimos quadrados Least Squares Collocation LSC). Outro objetivo deste trabalho é verificar a potencialidade dos mais recentes Modelos Globais do Geopotential (MGGs) baseados nos dados do satélite GOCE. Para tanto, um breve estudo é realizado sobre os fundamentos matemáticos e os da Geodésia Física. Algumas características dos MGGs são discutidas, bem como uma visão global das novas missões gravimétricas. Uma atenção especial é dada a missão do satélite GOCE. A teoria referente à integral de Stokes e a colocação por mínimos quadrados são outros temas discutidos no trabalho. A decomposição espectral foi empregada no cálculo dos modelos geoidais e a componente de longo comprimento de onda foi representada pelo modelo EGM2008 até grau e ordem 150 e 360 e aqueles baseados na missão GOCE até 150. Os modelos foram comparados entre si em termos do resíduo da altura geoidal e na forma absoluta e relativa por meio das estações GPS/RN. Os resultados apontaram consistência entre os modelos em termos de diferença média quadrática. Também foi realizado um estudo na região montanhosa a fim de verificar o comportamento das metodologias; os resultados mostraram que a LSC é menos consistente do que a FFT. No que diz respeito aos modelos baseados na missão GOCE, 13 foram testados, além do EGM2008. A avaliação foi realizada em termos da comparação da altura geoidal obtidas pelos MGGs com as estações GPS/nivelamento e em termos do distúrbio de gravidade. A avaliação mostra que os modelos DIR_R3 e TIM_R3 apresentaram os resultados mais compatíveis. A escolha do estado de São Paulo está relacionada à grande quantidade de trabalhos geodésicos e atividades na área da engenharia e que necessitam da utilização de um sistema altimétrico. Além disso, a grande quantidade de dados gravimétricos e de estações GPS/RN é mais uma justificativa para a realização do trabalho.
APA, Harvard, Vancouver, ISO, and other styles
38

Gachari, Moses Karoki. "Determination of a gravimetric geoid for the eastern Africa region : the classical and spectral approaches." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337722.

Full text
APA, Harvard, Vancouver, ISO, and other styles
39

Ulotu, Prosper E. "Geoid model of Tanzania from sparse and varying gravity data density by the KTH method /." Stockholm : Skolan för Arkitektur och samhällsbyggnad, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10270.

Full text
APA, Harvard, Vancouver, ISO, and other styles
40

Yang, Hyo Jin. "Geoid Determination based on a Combination of Terrestrial and Airborne Gravity Data in South Korea." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1388677708.

Full text
APA, Harvard, Vancouver, ISO, and other styles
41

Ulotu, Prosper. "Geoid Model of Tanzania from Sparse and Varying Gravity Data Density by the KTH method." Doctoral thesis, KTH, Geodesi (stängd 20110301), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10270.

Full text
Abstract:
Developed countries are striving to achieve a cm geoid model. Most developing countries/regions think that the situation in their areas does not allow even a few decimetre geoid model. GNSS, which provides us with position, is one of the greatest achievements of the present time. Conversion of ellipsoidal height to orthometric height, which is more useful, requires an accurate geoid model. In spite of the sparse terrestrial gravity data of variable density, distribution and quality (a typical situation in developing countries), this study set out to develop as accurately as possibly achievable, a high quality geoid model of Tanzania. Literature review of three more preferred geoid methods came to a conclusion, that the Royal Institute of Technology of Sweden (KTH) method of least squares modification of Stokes formula (LSMS) with additive corrections (AC) is the most suitable for this research. However, even with a good method, the accuracy and the quality of a geoid model depend much on the quality of the data. In this study, a procedure to create a gravity database (GDB) out of sparse data with varying density, distribution and quality has been developed. This GDB is of high density and full coverage, which ensures presence of high and low gravity frequencies, with medium frequencies ranging between fair and excellent. Also an alternative local/regional Global Gravitational Model (GGM) validation method based on quality terrestrial point surface gravity anomaly has been developed. Validation of a GGM using the new approach of terrestrial point gravity and GPS/Levelling, gave the same results. Once satisfactorily proved, the method has extra advantages. The limits of Tanzania GDB (TGDB) are latitudes 15 ° S to 4 ° N and longitudes 26 ° E to 44 ° E . Cleaning and quality control of the TGDB was based on the cross validation (XV) by the Kriging method and Gaussian distribution of the XV residuals. The data used in the LSMS with AC to develop a new Tanzania gravimetric geoid model 2008, TZG08, are 1′ ×1′ clean and statistically tested surface gravity anomalies. 39,677 point gravity in land and 57,723 in the ocean were utilised. Pure satellite ITGGRACE03S GGM to degree 120 was used to determine modification parameters and long-wavelength component of the geoid model. 3′′ Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM), ITG-GRACE03S to degree 120 and EIGENCG03C to degree 360 combined GGM qualified to patch the data voids in accordance to the method of this research. TZG08 is referred to Geodetic Reference System 1980 (GRS80), and its extents are latitudes 12 ° S to 1 ° N and longitudes 29 ° E to 41 ° E . 19 GPS/levelling points qualified to assess the overall accuracy of TZG08 as 29.7 cm, and upon approximate removal of GPS and orthometric systematic effects, the accuracy of TZG08 is 27.8 cm. A corrector surface (CS) for conversion of GPS height to orthometric height referred to Tanzania National Height Datum (TNHD) has been created for a part of TZG08. Using the CS and TZG08, orthometric height of Mt. Kilimanjaro is re-established as it was in 1952 to be 5,895 m above the TNHD, which is still the official height of the mountain.

QC 20100813

APA, Harvard, Vancouver, ISO, and other styles
42

Schwabe, Joachim. "Regionale Geoidmodellierung in Polargebieten." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-172617.

Full text
Abstract:
Der regionalen Schwerefeldmodellierung in polaren Gebieten kommt in vielerlei Hinsicht eine besondere und wachsende Bedeutung zu. Einerseits sind hochauflösende und präzise Geoidmodelle eine wichtige Eingangsgröße bei der Untersuchung und Quantifizierung geophysikalischer, ozeanographischer bzw. glaziologischer Phänomene, z. B. bei der Bestimmung der mittleren dynamischen Ozeantopographie oder der Anwendung des Schwimmgleichgewichts im Bereich von Schelfeisen, Meereis oder subglazialen Seen. Zudem werden sie allgemein zur Referenzierung von Höhenmodellen benötigt. Andererseits sind, aufgrund der unvermeidbaren polaren Datenlücken von Satellitenbeobachtungen jenseits der Grenzbreite (sog. „Polloch“), terrestrische Schweredaten auch für die globale Schwerefeldmodellierung unerlässlich. Jedoch sind die verfügbaren terrestrischen (bodennahen) Schwerebeobachtungen insbesondere im Gebiet der Antarktis äußerst lückenhaft und heterogen. So entspricht das tatsächliche Auflösungsvermögen selbst aktueller kombinierter Schwerefeldmodelle wie EGM2008 oder EIGEN-6C über dem antarktischen Kontinent lediglich dem der reinen Satellitenmodelle aus GRACE bzw. GOCE. Des Weiteren sind Standardverfahren der regionalen Geoidmodellierung hier nicht ohne Weiteres anwendbar. Neben der Heterogenität der Daten als praktischer Herausforderung muss aus theoretischer Sicht dem zusätzlichen Dichtekontrast durch das Eis Rechnung getragen werden. Die vorliegende kumulative Dissertation greift diese Problematik auf. Während die einzelnen Publikationen die Ergebnisse ausgewählter regionaler Fallstudien präsentieren, soll die folgende zusammenfassende Abhandlung einen doppelten Bogen spannen, indem die geophysikalischen Phänomene gleichzeitig als zu untersuchende Anwendungsgebiete und als Einflussfaktoren im Kontext der regionalen Geoidmodellierung beschrieben werden. So wird am Beispiel der Weddellsee gezeigt, wie die Meereisbedeckung die Qualität und Zuverlässigkeit der mithilfe der Satellitenaltimetrie abgeleiteten Schwerefeldmodelle beeinträchtigt. Diese Modelle bilden derzeit die alleinige Datengrundlage für die hochauflösenden globalen Modelle im Gebiet des Antarktischen Ozeans. Zugleich wird anhand des verfeinerten regionalen Modells und daraus abgeleiteter geostrophischer Geschwindigkeiten demonstriert, dass selbst lückenhafte und heterogene terrestrische Daten hier einen wesentlichen Beitrag zur simultanen Kalibrierung und Vereinheitlichung des Datenbestandes leisten können. Im Ergebnis konnten in den küstennahen Gewässern Differenzen von mehreren Dezimetern gegenüber Geoidhöhen aus EGM2008 festgestellt werden, welche teils auf systematische Abweichungen und teils auf Rauschen im globalen Modell zurückzuführen sind. Über dem Festland erreicht dessen Vernachlässigungsfehler im quadratischen Mittel sogar 0,75 m und Maxima von über 3 m. Ein weiteres verfeinertes und, dank geeigneter Eingangsdaten, sehr genaues und hochauflösendes Geoidmodell wird für die Region um den Vostoksee in der Ostantarktis abgeleitet. In Kombination mit Eisoberflächenhöhen und Eisdicken gelingt es, das Schwimmgleichgewicht des subglazialen Sees nachzuweisen. Das gegenüber GOCE zusätzlich gewonnene Geoidsignal ist hier mit 0,56 m Standardabweichung zwar etwas kleiner, jedoch wird im Vergleich mit der residualen Auslenkung des Seespiegels (0,26 m Standardabweichung) auch für diese Anwendung der signifikante und gegenüber dem Auflösungsvermögen von GOCE auch notwendige Beitrag eines regionalen Geoidmodells deutlich. Für das hydrostatische Gleichgewicht eines subglazialen Sees ist streng genommen das tatsächliche Schwerepotential in Höhe des Seespiegels maßgeblich. Dessen Berechnung erfordert eine Fortsetzung des Störpotentials nach unten innerhalb der Topographie, welche konzeptionell in engem Zusammenhang mit dem bekannten Geoid-Quasigeoid-Separationsterm steht. Dessen oft angenommene Approximation mithilfe der Bougueranomalie kann, angesichts der heutigen Anforderungen an ein modernes zentimetergenaues Geoid, gerade in rauem Gelände zu ungenau sein. In Anlehnung an aktuelle Arbeiten auf diesem Gebiet wird ein verallgemeinerter und zugleich verfeinerter Ansatz zur praktischen Berechnung des Terms erarbeitet. Am Beispiel des Himalaya werden die einzelnen Anteile im Rahmen einer Simulationsstudie quantifiziert und insbesondere ihre Sensitivität gegenüber dem Integrationsradius der Topographie untersucht. Besonderes Augenmerk liegt ebenso auf dem indirekten Effekt der Topographie in Bezug auf das Potential, welcher, im Gegensatz zur Anwendung eines planaren Modells, in sphärischer Betrachtungsweise nicht verschwindet
In many respects, regional gravity field modeling in polar areas is of special, and growing, interest. On the one hand, high-resolution and precise geoid models are an important input parameter to investigate and quantify manifold geophysical, oceanographical and glaciological phenomena, e.g., the determination of the mean dynamic ocean topography, or the application of the hydrostatic equilibrium condition in the areas of ice shelves, sea ice, or subglacial lakes. Moreover, geoid models are in general needed as a reference for height models. On the other hand, because of the unavoidable polar data gaps in satellite measurements due to the inclination (the so-called “polar gap”), terrestrial gravity data are indispensable also for global gravity field modeling. However, the available terrestrial (ground-based) gravity datasets, in particular of Antarctica, are very sparse and heterogeneous. For example, over the Antarctic continent the true resolution of even the most recent combined global geopotential models such as EGM2008 or EIGEN-6C only corresponds to that of the satellite-only models derived from GRACE and GOCE, respectively. Furthermore, standard techniques of regional geoid modeling cannot be readily used in this area. Apart from the heterogeneity of the data as a practical challenge the additional density contrast implied by the covering sheet needs to be accounted for from the theoretical point of view. This complex situation is the starting point for the present cumulative dissertation. Whereas the individual publications present the results of selected regional case studies, the intention of the following summary is to draw an integrated picture aiming at explaining the geophysical phenomena as both applications and influencing factors in the context of regional geoid modeling. Using the example of the Weddell Sea it is shown how sea-ice coverage affects the quality and reliability of marine gravity field models derived from radar satellite altimetry. At present, these models are the only input data to the high-resolution global geopotential models. At the same time, the refined regional model and geostrophic velocities derived thereof are employed to demonstrate how even sparse and heterogeneous terrestrial gravity data may provide a contribution to simultaneously calibrate and unify the available datasets. As a result, near the coast differences at the order of some decimeters could be observed in comparison with EGM2008, originating partly from systematic effects and noise in the global model. In the continental areas, its omission error even yields a standard deviation of 0.75 m and attains a maximum of more than 3 m. Another refined and, owing to appropriate input data, very precise and highly resolving geoid model is derived for the region around subglacial Lake Vostok. In combination with ice-surface heights and ice thickness data it is used to provide observational evidence that the lake is in a state of hydrostatic equilibrium. There, the additional geoid signal w.r.t. GOCE is a bit smaller (0.56 m standard deviation). However, considering the residual deviations of the apparent lake level (0.26 m standard deviation) the significant and necessary, as compared to the resolution of GOCE, contribution of a regional geoid model to this application is shown. In a strict sense, the relevant quantity to evaluate the hydrostatic equilibrium condition of a subglacial lake is the actual geopotential at the anticipated lake level. Its computation requires a downward continuation of the disturbing potential inside the topography, which is closely related to the concept of the well-known geoid-quasigeoid separation term. In the past, this term was frequently described as an approximation by means of the Bouguer anomaly. However, considering the modern requirements of the “one-centimeter geoid” this approximation may be too coarse over rough terrain. Following recent works in this field, a generalized yet refined approach for practical implementation of the term is developed. The individual constituents of the term are quantified. In particular, their sensitivity against the radius up to which topography is taken into account is investigated. For this simulation study, the Himalaya mountain region served as test area. Furthermore, special focus is given to the indirect of topography on the potential which, contrary to applying a planar model, does not vanish in the spherical approach
APA, Harvard, Vancouver, ISO, and other styles
43

Lorant, Foldvary. "Geoid Height Variations Caused by Geophysical Fluids and Their Possible Recovery by Future Satellite Gravity Missions." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150837.

Full text
APA, Harvard, Vancouver, ISO, and other styles
44

Stewart, Michael Paul. "Computation of a gravimetric geoid for the British Isles : an assessment of Fourier and classical techniques." Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/13023.

Full text
Abstract:
Some 250000 point gravity data for a 900x1 000km area covering the British Isles and the North Sea have been combined with a detailed topographic model on land and with a selection of global geopotential models in a high resolution, high precision geoid computation using two different techniques. The gravity data, comprising bouguer anomalies on land and free air anomalies at sea, together with the long wavelength gravity effect of the topographic model, were detrended with free air anomalies calculated on the ellipsoid from a high degree and order spherical harmonic geopotential model. The residual anomalies and the condensed short wavelength topography were transformed to the potential using both a fouricr technique and a classical Stokes' algorithm. The results were retrendcd with the geopotential model to produce absolute geoid heights. For each method, long wavelength residuals in the detrended gravity anomalies, caused by errors in the geopotential models, generate significant long wavelength errors which propagate through to the final geoid solution. It was found that these errors could be minimised by tapering the data and altering the shape of the data set, in the case of the fourier technique, and by using Meissl's modification to Stokes' function in the case of the classical technique. Long wavelength geoid discrepancies between different algorithms and detrending with different global gravity models involved slopes of typically less than 2cm/100km. For the cumulative effect of wavelengths between about 4 and 200km, computed geoids differed at the 1cm level. For local gravity field computations, the fourier technique was found to be 104 quicker than the classical method, for no appreciable loss in accuracy. Comparisons with short-baseline GPS-derived relative heights showed them to agree with the gravimetric geoid solutions at the 4cm level. Preliminary relative geoid heights derived from longer baseline GPS surveys agree with relative gravimetric geoid heights to 5cm/100km. Internal estimates give absolute long wavelength errors in gravimetric geoids to be approximately 2cm/100km, suggesting that the GPS observations so far available have not always achieved the accuracy of the gravimetric geoid computations. A comparison of geoid solutions from this project with the previous best geoid over the British Isles, EGG1, showed the new solutions to have a greatly improved resolution.
APA, Harvard, Vancouver, ISO, and other styles
45

Zhang, Kefei. "An evaluation of FFT geoid determination techniques and their application to height determination using GPS in Australia." Curtin University of Technology, School of Surveying and Land Information, 1997. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=11047.

Full text
Abstract:
A new, high resolution, high precision and accuracy gravimetric geoid of Australia has been produced using updated data, theory and computational methodologies. The fast Fourier transform technique is applied to the computation of the geoid and terrain effects. The long, medium and short wavelength components of the geoid are determined from the OSU91A global geopotential model, 2'x2' (residual gravity anomalies in a 3 degrees cap and 1'x1' digital terrain model (DTM), respectively.Satellite altimeter gravity data have been combined with marine gravity data to improve the coverage of the gravity data, and thus the quality of the geoid. The best gridding procedure for gravity data has been studied and applied to the gravity data gridding. It is found that the gravity field of Australia behaves quite differently. None of the free-air, Bouguer or topographic-isostatic gravity anomalies are consistently the smoothest. The Bouguer anomaly is often rougher than the free-air anomaly and thus should be not used for gravity field gridding. It is also revealed that in some regions the topography often contains longer wavelength features than the gravity anomalies.It is demonstrated that the inclusion of terrain effects is crucial for the determination of an accurate gravimetric geoid. Both the direct and indirect terrain effects need to be taken into account in the precise geoid determination of Australia. The existing AUSGEOID93 could be in error up to 0.7m in terms of the terrain effect only. In addition, a series of formulas have been developed to evaluate the precision of the terrain effects. These formulas allow the effectiveness of the terrain correction and precision requirement for a given DTM to be studied. It is recommended that the newly released 9"x9" DTM could be more effectively used if it is based on 15"x15" grid.It is estimated from comparisons with Global ++
Positioning System (GPS) and Australian Height Datum Data that the absolute accuracy of the new geoid is better than 33cm and the relative precision of the new geoid is better than 10~20cm. This new geoid can support Australian GPS heighting to third-order specifications.
APA, Harvard, Vancouver, ISO, and other styles
46

Rocha, César Peixoto da. "Obtenção e análise de azimutes por astronomia clássica e pelo sistema de posicionamento global." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/18/18137/tde-05032018-160342/.

Full text
Abstract:
O principal objetivo desse trabalho é caracterizar os métodos e processos que podem ser utilizados para obter melhores resultados dos azimutes sob a ótica da Astronomia Clássica e pelo Sistema de Posicionamento Global, levando em conta as diferentes natureza do tratamento aplicado às observações. Procurou-se também estabelecer a fronteira no comprimento das linhas Base, em que os resultados obtidos através de processos ela Astronomia Clássica tenham melhor precisão que os obtidos através dos recursos do Sistema de Posicionamento Global, além da caracterização e definição dos sistemas de referência e posicionamento, tratamentos necessários para minimizar os erros das observações e definição dos azimutes tratados pelas Engenharias.
The essential objective of this work is to characterize wich methods and processes should be used for obtain better results of the azimuths under the optics of the classic Astronomy and for the Global Positioning System, taking into account the different natures of the treatment aplied the observations. lt was also tried to establish the border in the length of base Iines, in that the results by process of the astronomy classic results of better quality that obtained by Global Positioning System, characterization and definition of the reference systems and positioning, necessary treatments to minimize the mistakes of the observations, and definition of the azimuths treated by Engineerings.
APA, Harvard, Vancouver, ISO, and other styles
47

Alves, Alexandre de Paula. "Sobre a técnica Fast Collocation (colocação rápida) na determinação do geóide do estado de São Paulo utilizando dados das missões CHAMP e GRACE." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/11269.

Full text
Abstract:
Os objetivos deste trabalho são: determinar o geóide do Estado de São Paulo (SP) pela técnica matemática Fast Collocation utilizando o modelo do geopotencial CG01c, derivado das novas missões gravimétricas de satélite CHAMP e GRACE, avaliar esse geóide através de estações com alturas geoidais conhecidas e do geóide calculado por Souza (2002), e apresentar uma nova abordagem que amplia a idéia sobre o sensoriamento remoto. O modelo do geopotencial CG01c, obtido com dados das missões CHAMP, GRACE e dados de superfície, e desenvolvido até o grau e ordem 360, foi utilizado para geração de anomalias gravimétricas, as quais foram subtraídas das anomalias gravimétricas terrestres, gerando as anomalias gravimétricas residuais. Essas anomalias residuais serviram de dados de entrada no programa FASTCOL para gerar as alturas geoidais residuais. A essas alturas geoidais residuais foi adicionado o modelo CG01c, representativo dos longos comprimentos de onda do campo de gravidade terrestre, produzindo-se o modelo geoidal chamado GEÓIDESP_FC_2007. Este geóide foi avaliado e posteriormente comparado com o Modelo Digital do Geóide Regular (MDGR). Ao final, argumentos foram apresentados para justificar o estudo do campo de gravidade da Terra no âmbito do sensoriamento remoto.
The objectives of this work are: to determine the geoid of the São Paulo (SP) State applying the mathematical technique so-called Fast Collocation using the CG01c geopotential model, from the new satellite gravity missions CHAMP and GRACE, to evaluate that geoid by stations with known geoidal heights and by the geoid determined by Souza (2002), and to show a new approach that enlarges the idea about the remote sensing. The CG01c geopotential model, obtained from missions CHAMP, GRACE and surface data, and developed up to degree and order 360, it was used to obtain the gravity anomalies, which were subtracted of the terrestrial gravity anomalies, yielding the residuals gravity anomalies. These residuals gravity anomalies it was input to the FASTCOL software to yield the residuals geoidal heights. The CG01c geopotential model, representative of the long wavelengths of the earth gravity field, was added to the residuals geoidal heights, yielding the geoid model so-called GEÓIDESP_FC_2007. This geoid was evaluated and later compared with the Modelo Digital do Geóide Regular (MDGR). At the end, arguments were presented to justify the study of the earth gravity field in the scope of the remote sensing
APA, Harvard, Vancouver, ISO, and other styles
48

Sekhar, Pavithra. "Three-Dimensional Spherical Modeling of the Mantles of Mars and Ceres: Inference from Geoid, Topography and Melt History." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/46873.

Full text
Abstract:
Mars is one of the most intriguing planets in the solar system. It is the fourth terrestrial planet and is differentiated into a core, mantle and crust. The crust of Mars is divided into the Southern highlands and the Northern lowlands. The largest volcano in the solar system, Olympus Mons is found on the crustal dichotomy boundary. The presence of isolated volcanism on the surface suggests the importance of internal activity on the planet. In addition to volcanism in the past, there has been evidence of present day volcanic activity. Convective upwelling, including decompression melting, has remained an important contributing factor in melting history of the planet. In this thesis, I investigate the production of melt in the mantle for a Newtonian rheology, and compare it with the melt needed to create Tharsis. In addition to the melt production, I analyze the 3D structure of the mantle for a stagnant lithosphere. I vary different parameters in the Martian mantle to understand the production of low or high degree structures early on to explain the crustal dichotomy. This isothermal structure in the mantle contributes to the geoid and topography on the planet. I also analyze how much of the internal density contributes to the surface topography and areoid of Mars. In contrast to Mars, Ceres is a dwarf planet in the Asteroid belt. Ceres is an icy body and it is unclear if it is differentiated into a core, mantle and crust yet. However, studies show that it is most likely a differentiated body and the mantle consists of ice and silicate. The presence of brucite and serpentine on the surface suggests the presence of internal activity. Being a massive body and also believed to have existed since the beginning of the solar system, studying Ceres will shed light on the conditions of the early solar system. Ceres has been of great interest in the scientific community and its importance has motivated NASA to launch a mission, Dawn, to study the planet. Dawn will collect data from the dwarf planet when it arrives in 2015. In my modeling studies, I implement a similar technique on Ceres, as followed on Mars, and focus on the mantle convection process and the geoid and topography. The silicate-ice mixture in the mantle gives rise to a non-Newtonian rheology that depends on the grain size of the ice particle. The geoid and topography observed for different differentiated scenarios in my modeling can be compared with the data from the Dawn mission when it arrives at Ceres in 2015.
Ph. D.
APA, Harvard, Vancouver, ISO, and other styles
49

Ågren, Jonas. "Regional Geoid Determination Methods for the Era of Satellite Gravimetry : Numerical Investigations Using Synthetic Earth Gravity Models." Doctoral thesis, KTH, Infrastructure, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-55.

Full text
Abstract:

It is the purpose of this thesis to investigate different regional geoid determination methods with respect to their feasibility for use with a future GOCE satellite-only Earth Gravity Model (EGM). This includes investigations of various techniques, which involve different approximations, as well as the expected accuracy. Many, but not all, of these tasks are tested by means of Synthetic Earth Gravity Models (SEGMs). The study is limited to remove-compute-restore methods using Helmert condensation and to Sjöberg's combined approach (method with additive corrections).

First, a number of modifications of Stokes' formula are tested with respect to their compatibility with a GOCE EGM having negligible commission error. It is concluded that the least squares modification method should be preferred.

Next, two new point-mass SEGMs are constructed in such a way that the resulting models have degree variances representative for the full and topographically reduced gravity fields, respectively. These SEGMs are then used to test different methods for modified Stokes' integration and downward continuation. It is concluded that the combined method requires dense observations, obtained from the given surface anomalies by interpolation using a reduction for all known density anomalies, most notably the topography. Examples of other conclusions are that the downward continuation method of Sjöberg (2003a) performs well numerically.

To be able to test topographic corrections, another SEGM is constructed starting from the reduced point-mass model, to which the topography, bathymetry and isostatic compensation are added. This model, which is called the Nordic SEGM, is then applied to test one strict and one more approximate approach to Helmert's condensation. One conclusion here is that Helmert's 1st method with the condensation layer 21 km below sea level should be preferred to Helmert's 2nd condensation strategy.

The thesis ends with a number of investigations of Sjöberg's combined approach to geoid determination, which include tests using the Nordic SEGM. It is concluded that the method works well in practice for a region like Scandinavia. It is finally shown how the combined strategy may preferably be used to estimate height anomalies directly.

APA, Harvard, Vancouver, ISO, and other styles
50

Ågren, Jonas. "Regional geoid determination methods for the era of satellite gravimetry : numerical investigations using synthetic earth gravity models /." Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-55.

Full text
APA, Harvard, Vancouver, ISO, and other styles
You might also be interested in the bibliographies on the topic 'GeoIP' for other source types:
Journal articles Books
We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!

To the bibliography