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Joodaki, Gholamreza. "Earth Mass Change Tracking Using GRACE Satellite Gravity Data." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23969.
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This project is dealing with the estimation of present-day Earth’s mass transport and its redistribution by using observations from Gravity Recovery and Climate Experiment (GRACE) satellite mission. GRACE measures the gravity fluctuations which are primarily related to redistribution of water around the globe. GRACE data has yield profound new insights into melting rates of ice sheets and mountain glaciers, land hydrology, ocean circulation, and sea level rise. In this project, first, the ice melting rate in the Greenlandic ice sheet is studied. This is done by analyzing the time series of monthly GRACE release 04 gravity field solutions from three different data sets, CSR (Center for Space Research), GFZ (Geoforschungszentrum), and JPL (Jet Propulsion Laboratory) with respect to their long-term temporal changes. The data are de-striped by applying a non-isotropic filter. Also, a method for reducing the leakage effects is developed. As an example, the ice mass balance is estimated of -163 ± 20 Gt/yr based on the CSR release 04 and smoothing by a parameter of a =1013 during April 2002 to February 2010. The results also show that the spatial distribution of the ice mass loss is changing with time and the ice mass loss is accelerating. For example, its acceleration is a rate of -32±6 Gt/yr2 during 2002 to 2011. The second part of this project is concern with the determination of water mass changes in the Nordic Seas. It is determined by analyzing the time series of monthly GRACE level 2 release 04 data from GFZ during October 2002 to October 2010. The striping errors are reduced by using a non-isotropic filter and the data are smoothed by a parameter of a =1014 according to Gaussian smoothing radius of 530 km. The time series of water mass changes are used to study the steric sea height variations over the Nordic Seas during the same period of study. This is done by analyzing the time series of monthly sea level anomaly from ENVISAT (Environmental Satellite) altimetry data, cycles 10 to 93, among the time series of water mass changes. The results show that the interdisciplinary nature of the GRACE measurements have opened up the unique opportunity to enhance our knowledge on the interaction between Earth system components and their response to climate variability. In the last part of this project, variations of the continental total water storage, total groundwater storage, and anthropogenic contributions across the Middle East are studied. By using a mascon analysis method and GRACE level 2 release 05 data from CSR during February 2003 to December 2012, the time series of total water storage, total ground water storage and anthropogenic contributions are estimated over this region. The region is subdivided to seven mascons including Iran, Iraq, Syria, eastern Turkey (east of 35º longitude), northern and southern Saudi Arabia (north and south of 25º latitude), and the region immediately west of Caspian Sea. The total groundwater storage, and anthropogenic contributions are separated from the total water storage by using the CLM4.5 (version 4.5 of the Community Land Model) hydrological model. The results show that Iran with a rate of 25±6 Gt/yr has the most groundwater loss rate during February 2003 to December 2012 in this region. The Iran’s rate of groundwater loss from the GRACE data is supported by an analysis of in situ well data from across Iran. The results also show that the GRACE mission is able to monitor monthly water storage changes within river basins and aquifers that are 200,000 km2 or larger in area, and, can contribute to water management at regional and national scales, and to international policy discussions as well.
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Han, Shin-Chan. "Efficient global gravity field determination from satellite-to-satellite tracking." Columbus, Ohio : Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1061995200.
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Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xvii, 198 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Christopher Jekeli, Dept. of Geodetic Science and Surveying. Includes bibliographical references (p. 192-198).
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Yamamoto, Keiko. "Study on regional scale mass variation using GRACE satellite gravity data." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/59309.
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Habana, Nlingilili Oarabile Kgosietsile. "Gravity Recovery by Kinematic State Vector Perturbation from Satellite-to-Satellite Tracking for GRACE-like Orbits over Long Arcs." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1578042687104082.
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Scheller, Marita. "Bestimmung hydrologischer Massenvariationen aus GRACE-Daten am Beispiel sibirischer Flusssysteme." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-103852.
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Aus Beobachtungsdaten der Satellitenmission GRACE (Gravity Recovery and Climate Experiment) können Variationen des Erdschwerefeldes auf großen räumlichen Skalen mit hoher Genauigkeit abgeleitet werden. Die Variationen auf zeitlichen Skalen von mehreren Tagen bis Wochen und räumlichen Skalen von wenigen hundert Kilometern sind insbesondere auf Änderungen der kontinentalen Wassermassen zurückzuführen. Die vorliegende Promotionsarbeit beschäftigt sich mit der Bestimmung hydrologischer Massenvariationen aus GRACE-Daten am Beispiel der vier größten sibirischen Flusseinzugsgebiete Ob, Jenissei, Lena und Kolyma. Darauf aufbauend sollen in Kombination mit atmosphärischen Daten der NCEP-Reanalyse Süßwassereinträge in den Arktischen Ozean abgeleitet werden. Die Süßwassereinträge beeinflussen nachhaltig den Salzgehalt und damit das ozeanographische Regime des Arktischen Ozeans, welcher wiederum einen Einfluss auf die globale thermohaline Zirkulation hat. Da die großen Strömungen des Weltozeans einen grundlegenden Faktor des globalen Klimageschehens darstellen, sind die Änderungen des Süßwassereintrages ein wichtiger Aspekt hinsichtlich prognostizierter Klimatrends. Der Abfluss kann an ausgewählten Messpunkten mit einer hohen zeitlichen Auflösung beobachtet werden. Die Datenreihen weisen jedoch immer wieder Lücken auf und die bodengebundenen Messungen sind oft schwierig und kostenintensiv. Messmethoden, die unabhängig vom Zugang ins Messgebiet sind, können einen großen Fortschritt bei der Beobachtung sich ändernder Massen und Süßwasserflüsse leisten und damit einen Beitrag für ein besseres Verständnis gekoppelter komplexer Prozesse der Arktis liefern. Da die Fehlerstruktur der GRACE-Daten komplex und bis heute nicht vollständig verstanden ist, erfolgt zunächst eine Untersuchung des GRACE-Fehlerhaushaltes. Zudem werden die Fehlereffekte aufgrund des begrenzten räumlichen Spektrums und damit einhergehender Leck-Effekte auf Ebene von Gebietsmittelwerten analysiert und Lösungsvorschläge diskutiert. Dabei sind folgende Aspekte von Bedeutung: Erweiterung der GRACE-Datenreihe um geeigente Terme ersten Grades und Abschätzung von Leck-Effekten, verursacht durch das begrenzte Spektrum der Kugelfunktionsentwicklung. Leck-Effekte aufgrund ozeanischer Signalanteile sind bzgl. der Einzugsgebiete sibirischer Flusssysteme klein (< 1%), wohingegen Leck-Effekte aufgrund kontinentaler Signalanteile je nach Gebietsgröße relative Fehler von 8-17% nach sich ziehen. Die größten Fehlereffekte resultieren jedoch aus den Koeffizienten hoher Grade. Die Filterung der GRACE-Daten ermöglicht die Glättung fehlerbehafterer Signalanteile. Neben den in der Literatur gängigen Filtern wurde im Rahmen der Arbeit ein Kombinationsfilter entwickelt, welches auf Basis von räumlichen Vorinformationen aus Hydrologiemodellen signifikante Signalstrukturen in den GRACE-Datenreihen detektiert. Somit muss lediglich ein Restsignal mittels Filterung gedämpft werden. Mit dem Kombinationsfilter können sowohl feinere Signalstrukturen als auch größere Signalamplituden auf Land erhalten werden. Im Vergleich zu reinen Filteranwendungen werden hier Gesamtsignalstärke, Amplitude und Phase des jährlichen Signals gut repräsentiert. Darauf aufbauend lassen sich, in Kombination mit atmosphärischen Daten, Abflüsse für die sibirischen Flusssysteme aus GRACE-Wasserspeichervariationen ableiten. Die Validierung der berechneten Abflüsse anhand beobachteter Abflüsse zeigt eine hohe Übereinstimmung von bis zu 83%. Eine Gegenüberstellung des berechneten Abflusses der Lena mit Wasserstandsmessungen im Mündungsbereich zeigt zudem einen Zusammenhang zwischen dem maximalen Abfluss im Frühjahr und einer Zunahme des Wasserstandes in der LaptewseeThe satellite mission GRACE (Gravity Recovery and Climate Experiment) observes the earth's gravity field on temporal scales of a few days to several weeks and spatial scales of a few hundred kilometers with high accuracy. A large part of the variations of the gravity field originate from hydrological mass changes on the continents. The dissertation discusses the determination of hydrological mass variations from GRACE for the Siberian water systems of the rivers Ob, Yenisey, Lena and Kolyma. The mass variations from GRACE data are combined with atmospheric data of the NCEP reanalysis to calculate the freshwater fluxes in the Arctic Ocean. The freshwater fluxes strongly influences the salinity and the oceanographic regime of the Arctic Ocean. In turn, the Arctic Ocean controls the global thermohaline circulation which is very important for the global climate. Because these large currents of the ocean influence the global climate, the changes of the freshwater fluxes in the Arctic Ocean are an important factor for the global climate change. The runoff can be measured pointwise with high temporal resolution, but measurements in the high latitudes are difficulty and expensive. Independent methods to measure the mass changes in the Arctic can help to determine the freshwater fluxes on large spatial scales, and contribute to understand the coupled and complex processes of the Arctic. Until present, the complex error structure of the GRACE data are not fully understand. The dissertation examines the errors and analysizes the leakage caused by the limited spectrum of the Stokes coefficients. A proposal for a solution will be discussed. The following steps are important: Expanding the GRACE data with adequate terms of degree one; Valuation of leakage errors because of the limited spectrum. Leakage due to oceanographic signals of the Arctic Ocean are small (< 1%). Leakage errors due to signals on land produces relative errors of basin averages of 8-17%. Beyond that, the largest errors are caused by the coefficients of higher degree. Filtering is an effective method to damp the error signals. In addition to the common filters described in the literature, a filter method, called composite filter, was created. Significant structures from hydrological models can be deteceted in the GRACE data without any other filtering. Only the residual signals should be filtered by using one of the common filters. In comparison to the common filters, the composite filter represents the signal strength, the signal structures, the amplitude and the phase of the saisonal signal on the continents much better. Combining hydrological mass variations from GRACE data with atmospheric data (for example the NCEP reanalysis) the runoff of the four Siberian river systems can be calculated. The validation of the calculated runoff using observations leads to a good agreement (83% for Yenisey and Lena). Furthermore, it is possible to combine the runoff of a river system with measurements of water level and salinity in the Arctic Ocean. The high runoff of the Lena river system in spring is visible in the water level changes in the Laptev sea
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Poropat, Lea [Verfasser]. "Importance of numerical ocean modelling and in situ ocean bottom pressure observations for satellite gravimetry from GRACE and GRACE-FO / Lea Poropat." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1215571895/34.
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Sutton, Eric K. "Effects of solar disturbances on the thermosphere densities and winds from CHAMP and GRACE satellite accelerometer data." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3303901.
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Kazemzadeh, Samimi Anahita. "Estimation of regional groundwater level through calibration of GRACE satellite data : A case study in southern half of Sweden." Thesis, Högskolan i Gävle, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-13634.
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Lombardo, Marco. "Numerical simulations of the orbit determination of a small sat mission for gravity investigations based on Satellite-to-Satellite Tracking." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18501/.
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In the recent years small satellites technology is growing up very fast. The use of a small sized spacecraft allows to reduce the costs of construction and launch without make particular compromise in terms of scientific objectives. Recently the small satellites have been used also as complement in a deep space mission and so new engineering challenges have born.
The purpose of this master thesis rely on a particular small satellites mission concept that would improve the gravity investigations accuracy of a target body but with a lower cost. This mission case is based on the employment of a pair
of small satellites that use the Satellite-to-Satellite Tracking technique to generates the observable quantities used for the orbit determination process and for the scientific analysis. These observables are two-way Doppler data obtained from the frequency shift of a stable microwave carrier transmitted between the two spacecrafts. Through these measurements it is possible to determine the static
and dynamic gravity field of a body. The utilization
of the SST, together with the small satellites technology, would certainly reduce the complexity and the costs, with an increment of estimation accuracy, but with the introduction of new potential engineering problems.
The targets of the proposed SST mission concept are Titan, Enceladus and Europa.
In each of these mission cases the two smallsats are placed on the same orbit, with a given angular separation.
The objectives of this thesis were focused on the analysis of the SST technique, the numerical simulation of the orbit determination of the spacecrafts and the obtainable accuracy of the moon's gravity field estimation. Following these targets different orbital geometries were studied, to identify the most promising configurations.
All the numerical evaluations have been conducted with the astro available at the Radio Science and Planetary Exploration Laboratory of the University of Bologna.
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Vishwakarma, Bramha Dutt [Verfasser], and Nico [Akademischer Betreuer] Sneeuw. "Understanding and repairing the signal damage due to filtering of mass change estimates from the GRACE satellite mission / Bramha Dutt Vishwakarma ; Betreuer: Nico Sneeuw." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1138234877/34.
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Dietrich, Reinhard, Martin Horwath, and Andreas Groh. "Beitrag der polaren Eismassen zum globalen Meeresspiegelanstieg aus Daten der Satelliten-Schwerefeldmission GRACE." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-26330.
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Die mit dem globalen Klimawandel einhergehende Zunahme der mittleren Jahrestemperatur führt zu einem Anstieg des mittleren Meeresspiegels. Hierzu trägt auch das Schmelzwasser der kontinentalen Eismassen bei. Über die Bestimmung der kontinentalen Eismassenänderungen kann somit auf deren Beitrag zum globalen Meeresspiegelanstieg geschlossen werden. Eismassenänderungen spiegeln sich in Variationen des Gravitationsfeldes der Erde wieder. Diese Variationen werden durch die Satelliten- Schwerefeldmission GRACE monatlich bestimmt. Am Institut für Planetare Geodäsie wurden die Eismassenänderungen des Antarktischen und Grönländischen Eisschildes aus 61 GRACEMonatslösungen für den Zeitraum August 2002 bis Januar 2008 abgeleitet. Sie belaufen sich auf -109 ± 48 bzw. -193 ± 22 Gt/a, was einem äquivalenten Meeresspiegelanstieg von 0.31 bzw. 0.55 mm/a entsprichtThe mean annual temperature rise which goes hand in hand with global warming results in a mean sea level rise. Meltwater influx from continental ice masses is one component of this phenomenon. Hence, the determination of continental ice mass changes makes it possible to infer their contribution to the global mean sea level rise. Such mass variations induce changes in the Earth's gravity field, as observed on a monthly basis by the gravity field satellite mission GRACE. At the Institut für Planetare Geodäsie, mass changes across the ice sheets of Greenland and Antarctica have been derived from 61 GRACE monthly solutions for the period 08/2002 – 01/2008. These ice mass changes add up to -109 ± 48 and -193 ± 22 Gt/a, respectively. This equates to a sea level rise of 0.31 or 0.55 mm/a
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Lindgren, Carl. "Estimating groundwater changes in the Rufiji basin by using data from the GRACE satellites." Thesis, Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-105999.
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Filho, Flavio Guilherme Vaz de Almeida. "Variação temporal do campo gravitacional detectada pelo satélite GRACE: aplicação na bacia Amazônica." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3138/tde-10112009-094808/.
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O objetivo deste trabalho é investigar o processo das variações do campo gravitacional, obtidas através da missão espacial GRACE e seu relacionamento com a dinâmica das águas na região Amazônica. A partir disto, procurou-se desenvolver uma metodologia para as estimativas das cotas dágua em áreas inundáveis não monitoradas ou de difícil acesso. Para isso, os coeficientes de Stokes, disponibilizados pelo GRGS de Toulouse, foram convertidos, por um processo denominado inversão, no equivalente à altura dágua (EqW) para o período de aproximadamente 4 anos (julho de 2002 a maio de 2006) e os valores comparados às cotas do nível dágua in-situ obtidas pela Agência Nacional de Águas (ANA). A escolha da bacia Amazônica está relacionada ao fato da mesma apresentar, próximo ao centro, amplitudes de aproximadamente 1250 mm no nível do EqW, sendo as maiores do mundo. A regionalização dos modelos globais das variações deste campo pôde ser aplicada para uma boa estimativa nas cotas dágua in-situ. Assim, foram estimados os erros desta metodologia, que são da ordem de ~160 mm para o EqW, oriundos dos erros nos coeficientes de Stokes, truncamento do espectro e erros de vazamento de informações hidrológicas das bacias vizinhas. Esta metodologia trata, portanto, de estimar as cotas onde não existam estações de monitoramento, avaliando a ordem de grandeza dos erros. Por fim, são apresentadas cartas que relacionam hidrogeologicamente as defasagens apresentadas nos ciclos semi-anuais e as áreas onde a metodologia poderá ser melhor aplicada com estimativas mais precisas do EqW e com maior coerência entre os dados satelitais e terrestres.A comparison between vertically-integrated equivalent water height (EWH) derived from GRACE gravity anomalies with in situ water level time series measured at ground-based hydrometric stations (HS) in the Amazon basin is figure out in the thesis. A methodology for EWH estimation at ungauged sites is presented. The Stokes coefficients disponibilized by GRGS - Toulouse at a 10-day interval were converted into EWH for a ~4-year period (July-2002 to May-2006) using the methodology so-called inversion, and then compared to HS level. In the basin, the amplitudes of EWH signal are the largest on the Earth and can reach on the order of 1250 mm at the center of the basin (e.g. Manaus station). The uncertainties represent ~160 mm of EWH, including Stokes coefficient uncertainties, leakage errors and spectrum truncation. A methodology for acquire water level historical series at ungauged places is proposed with the estimated incertitude. A hydrological map is compared with a correlation chart and figure out areas where this methodology works better, in addition, compared also with shift phased semi-annual cycles.
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Casadei, Alessandro. "Simulazione di front-end GPS per la verifica di algoritmi di navigazione per satelliti LEO." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/6354/.
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Descrizione di un software di simulazione, realizzato attraverso la programmazione in Labview, che estrapola i dati immagazzinati nei file RINEX di navigazione e di osservazione della missione GRACE e li invia con le stesse modalità con cui lo farebbe il ricevitore OEM615 della NovAtel. L'obiettivo è creare un software che permetta di testare, nell'ambito della missione ESEO dell'ESA, il ricevitore GPS che farà parte del payoload della stessa missione, costituita da un micro-satellite che orbiterà in orbita bassa LEO, e che sarà composto da un ricevitore OEM615, da un'antenna GPS e da un processore di navigazione.
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Dieng, Habib Boubacar. "Variations actuelles du niveau de la mer." Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30003/document.
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Depuis le début des années 1990 on suit l'évolution globale du niveau de la mer grâce aux satellites altimétriques. Ils observent une hausse du niveau moyen global de la mer (GMSL) de 3.4 ± 0.4 mm/an sur la période 1993-2016 (ce qui représente le double de ce qui a été observé au cours du 20ème siècle par les marégraphes, hausse à 1.7 mm/an entre 1900 et 1990). Le GMSL présente aussi des fluctuations interannuelles qui peuvent atteindre quelques millimètres, surtout pendant les épisodes ENSO. Cette hausse n'est pas régionalement uniforme : elle a été 3 fois plus rapide que la hausse moyenne globale dans certaines zones entre 1993 et 2016. Au cours du 21ème siècle, on s'attend à une hausse accrue du GMSL pouvant aller jusqu'à 1 m à l'horizon 2100, avec une forte variabilité régionale. Il est donc important de comprendre l'évolution actuelle du niveau des océans qui constitue une menace sérieuse pour de nombreuses régions côtières basses souvent très peuplées. Cette thèse s'inscrit dans le contexte du projet niveau de la mer CCI (Climate Change Initiative) de l'Agence Spatiale Européenne (ESA) ayant pour objectif de fournir de meilleurs produits du niveau de la mer combinant les missions Topex/Poseidon, Jason-1/2, ERS-1/2 et Envisat. L'objectif premier de cette thèse est de valider ces produits SL_CCI du niveau de la mer en utilisant différentes approches, en particulier par l'étude du bilan (comparaison du GMSL observé avec la somme des différentes contributions : composante stérique, fonte des glaces continentales et transferts d'eau depuis les terres émergées). Un autre objectif est d'estimer les composantes du niveau de la mer mal connues, et tout particulièrement le contenu thermique de l'océan profond non mesurable par le système Argo, et la contribution du stock d'eau sur les continents. Ces travaux ont montré que la contribution de l'océan profond en dessous de 2000m est faible sur la période 2005-2013 et contenue dans la barre d'incertitudes des données (erreurs qui proviennent essentiellement, (1) des produits niveau de la mer altimétriques et des lacunes de la couverture géographique des données Argo dans la région Indonésienne pour la tendance et (2) des produits GRACE et Argo pour la variabilité interannuelle). Nos résultats et la méthode utilisée montrent que le niveau de la mer et ses composantes sont encore entachés d'erreurs importantes. Dans la deuxième partie, nous avons analysé l'influence du phénomène ENSO (El Niño et La Niña) sur les variations interannuelles du GMSL. Nous montrons que lors des évènements La Niña comme celui de 2010-2011, le déficit de précipitations sur l'océan (et l'excès sur les continents) conduit à une baisse temporaire de la masse de l'océan global et donc du niveau de la mer. C'est essentiellement la variation de masse de l'océan qui explique la variabilité interannuelle du niveau de la mer lors des évènements ENSO, et le déficit (La Niña) ou excès (El Niño) de masse se trouve confiné dans l'océan Pacifique tropical Nord. Pour finir, nous analysons l'évolution de la température moyenne de l'air et de l'océan en surface sur la période du "hiatus" (2003-2013). Nous montrons que ce hiatus, c'est à dire le ralentissement récent de la hausse de la température moyenne globale de la Terre est un phénomène quasi global, même si le Pacifique tropical Est s'est fortement refroidi. Cette "supposée" pause récente s'explique par la variabilité naturelle interne du climat. La Terre est toujours en état de déséquilibre énergétique dû à l'accumulation de gaz à effet de serre. Nous mettons en évidence le rôle de la variabilité naturelle à court terme sur les changements à plus long terme associés au réchauffement climatique anthropiqueSince the early 1990s sea level is routinely measured using high-precision altimeter satellites. These observe a rise in global mean sea level (GMSL) of 3.4 ± 0.4 mm/yr over the 1993-2016 period (which is twice what has been observed during the 20th century by the tide gauges, with a rise of 1.7 +/- 0.3 mm/yr). The interannual variability in the GMSL can reach several millimeters, especially during ENSO events. The rate of sea level rise is not regionally uniform. During the altimetry era, it was three times faster than the global mean in some areas. During the 21st century, we expect a greater rise of the GMSL than today, up to 1 m in 2100, with strong regional variability. It is therefore important to understand the current evolution of the sea level, since it represents a serious threat to many low coastal areas, often densely populated of the planet. My thesis research deals with the Sea Level CCI (Climate Change Initiative) project of the European Space Agency (ESA) which objective is to provide improved sea level products combining several altimetry missions, including Topex/Poseidon, Jason-1/2, ERS-1/2 and Envisat. The primary objective of my thesis was to validate the CCI sea level products using different approaches, in particular the sea level budget approach. It consists of comparing the observed GMSL with the sum of different contributions : the steric component, melting of continental ice and transfers of water between the land surface and oceans. Another objective was to estimate the poorly known components to sea level rise, in particular the heat content of the deep ocean not measurable by Argo, and the contribution of water storage on the land. My work has shown that the contribution of the deep ocean below 2000m to the rising sea level is small over the 2005-2013 periods and not significant compared to the data uncertainties. The main uncertainties come from: (1) -in terms of trend- the altimetry sea level products and gaps in the geographical coverage of Argo data in the Indonesian region, and (2) -in terms of interannual variability- the GRACE and Argo products. My results and the method used show that the sea level and its components are still affected by important errors. In the second part, I analyzed the influence of ENSO (El Niño and La Niña) on the interannual variations of the GMSL. I showed that during La Niña events, like that of 2010-2011, the rainfall deficit over the ocean (and excess over the continents) leads to a temporary decrease in the global ocean mass and therefore in the GMSL. This is essentially the ocean mass variation that explains the interannual variability of the GMSL during ENSO events. Furthermore, the deficit (La Niña) or excess (El Niño) ocean mass is confined in the north tropical Pacific Ocean. Finally, I analyzed the evolution of the average temperature of air and ocean surface over the period of the "hiatus" (2003-2013). I showed that this hiatus, i.e. the recent slowdown in the rise of the global mean Earth's temperature is an almost global phenomenon, though cooling of the tropical eastern Pacific has slightly contributed. This recent pause is attributable to natural internal climate variability. The Earth is indeed still in a state of energetic imbalance due to the accumulation of greenhouse gases. I highlighted the role of the natural variability that is superimposed to the anthropogenic global warming
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Vaz, De Almeida Flavio-Guilherm. "Etudes des variations temporelles du champ de pesanteur terrestre à partir des données de la mission GRACE : application au bassin amazonien." Toulouse 3, 2009. http://thesesups.ups-tlse.fr/583/.
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L'objectif de ce travail est d'analyser les variations temporelles du champ de gravité, déterminées par la mission spatiale Gravity Recovery and Climate Experiment (GRACE), et ses relations avec la dynamique des eaux dans la région Amazonienne. À ce titre, nous avons cherché à développer une méthodologie pour les estimations des stocks d'eau dans des zones innondables non contrôlées ou difficilement accessibles. Pour ce faire, les coefficients de Stokes, calculés par le Groupe de Recherche de Geodesie Spatiale (GRGS) de Toulouse, ont été convertis en hauteur d'eau équivalente (HEE, Equivalent water Height - EWH en anglais) sur une période d'environ 4 ans (juillet de 2002 à mai 2006). Les valeurs d'HEE ainsi obtenues ont été comparées aux niveaux d'eau in-situ collectés par l'Agence Nationale de lEau brésilienne (ANA). Le choix du bassin Amazonien pour ce travail tient au fait qu'il présente en son centre, des amplitudes d'environ 1250mm de HEE, soit les plus grandes du monde. Cette amplitude est validée indirectement par comparaison entre les déplacements crustaux verticaux équivalents à cette charge superficielle et les mouvements verticaux de la stations GPS permanente de Manaus, à proximité du centre du bassin. Nous estimons que les erreurs associées à ces HEE sont au maximum de l'ordre de ~160mm HEE. Elles proviennent des erreurs des coefficients de Stokes, de la troncation du spectre et des erreurs de contamination (leakage) d'informations hydrologiques des bassins voisins. Finalement, HEE et les données de hauteur d'eau sont comparées dans les fleuves en terme d'hydrogéologieThe objective of this work is to analyze the temporal variations of the gravitational field, determined by the space mission Gravity Recovery and Climate Experiment (GRACE), and its relationships to the dynamics of water in the Amazon basin area. For this reason, was developed a methodology to estimate the water level in not controlled stocks or difficult to reach floodplains. With this intention, the Stokes coefficients, calculated by the Groupe de Recherche de Geodesie Spatiale (GRGS) Toulouse-FR, were converted into equivalent water height (EWH) for a ~4-year period (July-2002 to May-2006). In this basin, the amplitudes of EWH signal are the largest on Earth and can reach about 1250mm at the center of the basin. Analysis of the uncertainties indicate that it represents ~160 mm of EWH in this basin, including Stokes coefficient uncertainties (~130 mm), leakage errors (12 ~ 21 mm) and spectrum truncation (10 ~ 15 mm). This amplitude was indirectly validated by the comparison between equivalent vertical crustal displacements due to surface water load and the vertical movements of the Manaus GPS permanent monitoring stations, near to the center of the basin. The values of EWH thus obtained were compared with the in-situ water level collected by the Brazilian National Agency of Water (ANA) at 233 ground-based hydrometric stations (HS). Although EWH and HS measure different water bodies, high correlation, up to ~80% in most of the cases, is detected. This high correlation allows adjusting linear relationships between both series for the major tributaries of the Amazon. The regression coefficients decrease from upstream to downstream along the rivers reaching the theoretical value 1 at the mouth of the Amazon in the Atlantic Ocean
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Sammari, Hédia. "Modèle de géoide marin dans la mer Égée par altimétrie satellitaire." Master's thesis, Université Laval, 2009. http://hdl.handle.net/20.500.11794/20511.
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Depuis les années 1990, l' altimétrie par satellites est entrée dans une phase opérationnelle, grâce à la couverture exceptionnelle procurée par la combinaison de plusieurs missions (TOPEX/POSEIDON, ERS-1/2, Jason-l , ENVISAT, GFO). Ces missions contribuent entre autres à l'étude des marées, de la circulation océanique et du climat global. Ainsi, l'altimétrie spatiale, au moyen d'un radar embarqué sur un satellite, permet de cartographier directement les hauteurs de la surface de la mer d'une manière continue et d'étudier la surface océanique moyenne et aussi le géoïde. Il s'agit dans cette étude de calculer un géoïde local en mer Égée en Méditerranée par l'analyse des mesures altimétriques du satellite Jason-l et du positionnement précis de marégraphes au sol. Une correction d'orbite des données altimétriques et une interpolation sur une grille régulière sont appliquées. La méthode d'interpolation spatiale du krigeage est utilisée pour le calcul du modèle du géoïde sur une grille régulière de la zone d 'étude. La validation externe du modèle s'appuie sur la comparaison avec des données in situ de marégraphe et des modèles existants tels que l'EGM 96.
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Ge, Shengjie. "GPS radio occultation and the role of atmospheric pressure on spaceborne gravity estimation over Antarctica." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1149070384.
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Bourda, Géraldine. "Rotation terrestre et Variations du champ de gravité : Etude et apport des missions CHAMP et GRACE." Phd thesis, Observatoire de Paris, 2004. http://tel.archives-ouvertes.fr/tel-00008286.
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La distribution des masses à l'intérieur de la Terre régit la vitesse de rotation terrestre, ainsi que le comportement de l'axe de rotation terrestre dans la Terre, et dans l'espace. Ces distributions de masses peuvent être mesurées depuis l'espace grâce aux satellites artificiels, dont l'orbitographie donne accès à la détermination du champ de gravité terrestre. Par conséquent, les variations temporelles du champ de gravité peuvent être reliées aux variations des paramètres d'orientation terrestre (via le tenseur d'inertie). Des progrès considérables ont été effectués ces dernières années dans la modélisation des effets des couches fluides. Et de nos jours, les mesures d'orientation terrestre dans l'espace obtenues par Interférométrie à très Longue Base (VLBI) ont une exactitude meilleure qu'une milliseconde de degré. Ceci permet de progresser dans la connaissance de la dynamique globale de la Terre. Mon travail de thèse a eu pour but d'utiliser la mesure du champ de gravité et de ses variations comme outil pour compléter la modélisation de la rotation terrestre. D'une part, en vue de l'utilisation des mesures du satellite GRACE, d'une grande précision, nous avons effectué des comparaisons précises des méthodes numériques d'intégration d'orbite de Cowell et d'Encke dans le logiciel GINS du GRGS. D'autre part, nous avons établi les liens théoriques entre les Paramètres d'Orientation Terrestres (EOP) et les variations des coefficients du champ de gravité. Ainsi, nous avons utilisé les données de variations temporelles des coefficients de degré 2 du géopotentiel pour en déduire leur influence sur la longueur du jour, le mouvement du pôle et la précession de l'équateur.
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Peterseim, Nadja Verfasser], Roland [Akademischer Betreuer] Pail, Urs [Akademischer Betreuer] Hugentobler, and Petrus Nicolaas Anna Maria [Akademischer Betreuer] [Visser. "TWANGS – High-Frequency Disturbing Signals in the 10 Hz Accelerometer Data of the GRACE Satellites / Nadja Peterseim. Gutachter: Urs Hugentobler ; Roland Pail ; Pieter N. A. M. Visser. Betreuer: Roland Pail." München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1058214233/34.
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Garcez, de Oliveira Krone Martins Alberto. "Plus loin avec la mission spatiale Gaia grâce à l'analyse des objets étendus." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14241/document.
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Ce travail a comme objectif principal de vérifier s’il est possible de faire de la science avec les observations d’objets étendus qui seront réalisées par la mission spatiale Gaia. Cette mission, l’un des plus ambitieux projets de l’Astronomie moderne,observera plus d’un milliard d’objets dans tout le ciel avec des précisions inédites, fournissant des données astrométriques, photométriques et spectroscopiques. Naturellement, en fonction de sa priorité astrométrique, Gaia a été optimisé pour l’étude d’objets ponctuels. Néanmoins, diverses sources associées à des émissions étendues seront observées. Ces émissions peuvent avoir une origine intrinsèque, telles que les galaxies, ou extrinsèque, telles que les projections d’objets distincts sur la même ligne de visée, et présenteront probablement de solutions astrométriques moins bonnes.Pour étudier ces émissions, leurs images bidimensionnelles doivent être analysées.Néanmoins, comme Gaia ne produit pas de telles données, nous avons commencé ce travail en vérifiant si à partir de ses observations unidimensionnelles il serait possible de reconstruire des images 2D d’objets dans tout le ciel.Nous avons ainsi estimé la quantité de cas sujets à la présence d’émissions étendues extrinsèques, et nous avons présenté une méthode que nous avons développée pour analyser leurs images reconstruites. Nous avons montré que l’utilisation de cette méthode permettra d’étendre le catalogue final de façon fiable à des millions de sources ponctuelles dont beaucoup dépasseront la magnitude limite de l’instrument.D’un autre coté, dans le cas d’émissions intrinsèques, nous avons premièrement obtenu une estimation supérieure du nombre de cas que Gaia pourra observer. Nous avons alors vérifié qu’après les reconstructions d’images, les codes que nous avons développés permettront de classifier morphologiquement des millions de galaxies dans les types précoce/tardif et elliptique/spirale/irrégulière. Nous avons de plus présenté une méthode que nous avons développée pour réaliser la décomposition bulbe/disque directement à partir des observations unidimensionnelles de Gaia de façon complètement automatique.Finalement nous avons conclu qu’il est possible d’utiliser beaucoup de ces données qui pourraient être ignorées pour faire de la science. Et que le fait de les exploiter permettra aussi bien la détection de millions d’objets qui dépassent la limite de magnitude de Gaia, que de mener des études sur la morphologie de millions de galaxies dont les structures ne peuvent être révélées qu’à partir de l’espace ou au moyen d’optique adaptative, augmentant un peu plus les horizons de cette mission déjà immenseThe main objective of this work is to determine whether it is possible to do science from the observations of extended objects that will be performed by the Gaia space mission. One of the most ambitious projects of modern Astronomy, this mission will observe more than one billion objects through out the sky, thus providing astrometric, photometric and spectroscopic data with unprecedented precision. Naturally, Gaia has been optimized for the study of point-like sources due to its astrometrical priority. Nevertheless, many sources associated with extended emission will be observed. The origins of these extended sources can be either intrinsic, such as galaxies, or extrinsic, such as projections of objects in the same line of sight. In both cases, these sources will have less than optimal astrometric solutions.In order to study those emissions, their two-dimensional images will be analyzed. Nonetheless, since Gaia will not acquire such images, we begin this work by checking whether it will be possible to reconstruct images anywhere in the sky from the satellite’s one-dimensional observations.Consequently, we, on the one hand, estimate the number of cases which will be subjected to the extrinsic extended emissions, present a method which we developed to analyze the reconstructed images by segregating the different sources and show that the adoption of this method will allow extending the catalogue reliably by millions of point sources, many of which are beyond the limiting magnitude of the instrument. On the other hand, regarding intrinsic extended emissions, we first obtain an upper limit estimate for the number of cases which Gaia will be able to observe ; then,we verify that the combination of image reconstructions and the use of the codes introduced here in will allow performing the morphological classification of millions of galaxies in early/late types and elliptical/spiral/irregular classes. Afterward,we present a method which we developed to decompose those galaxies into their bulge/disk components directly from the one-dimensional Gaia data in a completely automatic way. Finally, we conclude that it is possible to harness the data of many of the observations that might other wise be ignored to do science. Saving these data will allow the detection of millions of objects beyond Gaia’s limiting magnitude and the study of the morphology of millions of galaxies whose structures can only be probed from space or through the adoption of adaptive optics, thus somewhat expanding the horizons of this already comprehensive mission
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Jones, Fraser Black III. "G.R.A.C.E. satellite thermal model." Thesis, 2012. http://hdl.handle.net/2152/29163.
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I developed a thermal model of the Gravity Recovery and Climate Experiment satellite for the Center for Space Research to use in verifying their thermal models and for developing the next generation of satellites for their experiments. I chose COMSOL to model the satellite and used ProEngineer and 3Ds Max to generate the mesh from a .STEP file provided by DaimlerChrysler. I adjusted the model based on previous computer models and actual telemetry data from the GRACE satellite provided from 2002 through 2008. Using the model, I developed a sensitivity analysis of the satellites key thermal environment components and used that to recommend design changed for the next generation of satellites. Special attention should be given to redesigning the Star Camera Arrays and the heat transfer between the Main Equipment Platform and the Radiator.text
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Yirdaw-Zeleke, Sitotaw. "Implications of GRACE Satellite Gravity Measurements for Diverse Hydrological Applications." 2010. http://hdl.handle.net/1993/3944.
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Soil moisture plays a major role in the hydrologic water balance and is the basis for most hydrological models. It influences the partitioning of energy and moisture inputs at the land surface. Because of its importance, it has been used as a key variable for many hydrological studies such as flood forecasting, drought studies and the determination of groundwater recharge. Therefore, spatially distributed soil moisture with reasonable temporal resolution is considered a valuable source of information for hydrological model parameterization and validation. Unfortunately, soil moisture is difficult to measure and remains essentially unmeasured over spatial and temporal scales needed for a number of hydrological model applications.
In 2002, the Gravity Recovery And Climate Experiment (GRACE) satellite platform was launched to measure, among other things, the gravitational field of the earth. Over its life span, these orbiting satellites have produced time series of mass changes of the earth-atmosphere system. The subsequent outcome of this, after integration over a number of years, is a time series of highly refined images of the earth's mass distribution. In addition to quantifying the static distribution of mass, the month-to-month variation in the earth's gravitational field are indicative of the integrated value of the subsurface total water storage for specific catchments. Utilization of these natural changes in the earth's gravitational field entails the transformation of the derived GRACE geopotential spherical harmonic coefficients into spatially varying time series estimates of total water storage. These remotely sensed basin total water storage estimates can be routinely validated against independent estimates of total water storage from an atmospheric-based water balance approach or from well calibrated macroscale hydrologic models. The hydrological relevance and implications of remotely estimated GRACE total water storage over poorly gauged, wetland-dominated watershed as well as over a deltaic region underlain by a thick sand aquifer in Western Canada are the focus of this thesis.
The domain of the first case study was the Mackenzie River Basin wherein the
GRACE total water storage estimates were successfully inter-compared and validated with the atmospheric based water balance. These were then used to assess the WATCLASS hydrological model estimates of total water storage. The outcome of this inter-comparison revealed the potential application of the GRACE-based approach for the closure of the hydrological water balance of the Mackenzie River Basin as well as a dependable source of data for the calibration of traditional hydrological models.
The Mackenzie River Basin result led to a second case study where the GRACE-based total water storage was validated using storage estimated from the atmospheric-based water balance P-E computations in conjunction with the measured streamflow records for the Saskatchewan River Basin at its Grand Rapids outlet in Manitoba. The fallout from this comparison was then applied to the characterization of the Prairie-wide 2002/2003 drought enabling the development of a new drought index now known as the Total Storage Deficit Index (TSDI). This study demonstrated the potential application of the GRACE-based technique as a tool for drought characterization in the Canadian Prairies.
Finally, the hydroinformatic approach based on the artificial neural network (ANN) enabled the downscaling of the groundwater component from the total water storage estimate from the remote sensing satellite, GRACE. This was subsequently explored as an alternate source of calibration and validation for a hydrological modeling application over the Assiniboine Delta Aquifer in Manitoba. Interestingly, a high correlation exists between the simulated groundwater storage from the coupled hydrological model, CLM-PF and the downscaled groundwater time series storage from the remote sensing satellite GRACE over this 4,000 km2 deltaic basin in Canada.
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Scheller, Marita. "Bestimmung hydrologischer Massenvariationen aus GRACE-Daten am Beispiel sibirischer Flusssysteme." Doctoral thesis, 2012. https://tud.qucosa.de/id/qucosa%3A26475.
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Aus Beobachtungsdaten der Satellitenmission GRACE (Gravity Recovery and Climate Experiment) können Variationen des Erdschwerefeldes auf großen räumlichen Skalen mit hoher Genauigkeit abgeleitet werden. Die Variationen auf zeitlichen Skalen von mehreren Tagen bis Wochen und räumlichen Skalen von wenigen hundert Kilometern sind insbesondere auf Änderungen der kontinentalen Wassermassen zurückzuführen. Die vorliegende Promotionsarbeit beschäftigt sich mit der Bestimmung hydrologischer Massenvariationen aus GRACE-Daten am Beispiel der vier größten sibirischen Flusseinzugsgebiete Ob, Jenissei, Lena und Kolyma. Darauf aufbauend sollen in Kombination mit atmosphärischen Daten der NCEP-Reanalyse Süßwassereinträge in den Arktischen Ozean abgeleitet werden.
Die Süßwassereinträge beeinflussen nachhaltig den Salzgehalt und damit das ozeanographische Regime des Arktischen Ozeans, welcher wiederum einen Einfluss auf die globale thermohaline Zirkulation hat. Da die großen Strömungen des Weltozeans einen grundlegenden Faktor des globalen Klimageschehens darstellen, sind die Änderungen des Süßwassereintrages ein wichtiger Aspekt hinsichtlich prognostizierter Klimatrends. Der Abfluss kann an ausgewählten Messpunkten mit einer hohen zeitlichen Auflösung beobachtet werden. Die Datenreihen weisen jedoch immer wieder Lücken auf und die bodengebundenen Messungen sind oft schwierig und kostenintensiv. Messmethoden, die unabhängig vom Zugang ins Messgebiet sind, können einen großen Fortschritt bei der Beobachtung sich ändernder Massen und Süßwasserflüsse leisten und damit einen Beitrag für ein besseres Verständnis gekoppelter komplexer Prozesse der Arktis liefern.
Da die Fehlerstruktur der GRACE-Daten komplex und bis heute nicht vollständig verstanden ist, erfolgt zunächst eine Untersuchung des GRACE-Fehlerhaushaltes. Zudem werden die Fehlereffekte aufgrund des begrenzten räumlichen Spektrums und damit einhergehender Leck-Effekte auf Ebene von Gebietsmittelwerten analysiert und Lösungsvorschläge diskutiert. Dabei sind folgende Aspekte von Bedeutung: Erweiterung der GRACE-Datenreihe um geeigente Terme ersten Grades und Abschätzung von Leck-Effekten, verursacht durch das begrenzte Spektrum der Kugelfunktionsentwicklung. Leck-Effekte aufgrund ozeanischer Signalanteile sind bzgl. der Einzugsgebiete sibirischer Flusssysteme klein (< 1%), wohingegen Leck-Effekte aufgrund kontinentaler Signalanteile je nach Gebietsgröße relative Fehler von 8-17% nach sich ziehen. Die größten Fehlereffekte resultieren jedoch aus den Koeffizienten hoher Grade. Die Filterung der GRACE-Daten ermöglicht die Glättung fehlerbehafterer Signalanteile. Neben den in der Literatur gängigen Filtern wurde im Rahmen der Arbeit ein Kombinationsfilter entwickelt, welches auf Basis von räumlichen Vorinformationen aus Hydrologiemodellen signifikante Signalstrukturen in den GRACE-Datenreihen detektiert. Somit muss lediglich ein Restsignal mittels Filterung gedämpft werden. Mit dem Kombinationsfilter können sowohl feinere Signalstrukturen als auch größere Signalamplituden auf Land erhalten werden. Im Vergleich zu reinen Filteranwendungen werden hier Gesamtsignalstärke, Amplitude und Phase des jährlichen Signals gut repräsentiert. Darauf aufbauend lassen sich, in Kombination mit atmosphärischen Daten, Abflüsse für die sibirischen Flusssysteme aus GRACE-Wasserspeichervariationen ableiten. Die Validierung der berechneten Abflüsse anhand beobachteter Abflüsse zeigt eine hohe Übereinstimmung von bis zu 83%. Eine Gegenüberstellung des berechneten Abflusses der Lena mit Wasserstandsmessungen im Mündungsbereich zeigt zudem einen Zusammenhang zwischen dem maximalen Abfluss im Frühjahr und einer Zunahme des Wasserstandes in der Laptewsee.The satellite mission GRACE (Gravity Recovery and Climate Experiment) observes the earth's gravity field on temporal scales of a few days to several weeks and spatial scales of a few hundred kilometers with high accuracy. A large part of the variations of the gravity field originate from hydrological mass changes on the continents. The dissertation discusses the determination of hydrological mass variations from GRACE for the Siberian water systems of the rivers Ob, Yenisey, Lena and Kolyma. The mass variations from GRACE data are combined with atmospheric data of the NCEP reanalysis to calculate the freshwater fluxes in the Arctic Ocean. The freshwater fluxes strongly influences the salinity and the oceanographic regime of the Arctic Ocean. In turn, the Arctic Ocean controls the global thermohaline circulation which is very important for the global climate. Because these large currents of the ocean influence the global climate, the changes of the freshwater fluxes in the Arctic Ocean are an important factor for the global climate change. The runoff can be measured pointwise with high temporal resolution, but measurements in the high latitudes are difficulty and expensive. Independent methods to measure the mass changes in the Arctic can help to determine the freshwater fluxes on large spatial scales, and contribute to understand the coupled and complex processes of the Arctic. Until present, the complex error structure of the GRACE data are not fully understand. The dissertation examines the errors and analysizes the leakage caused by the limited spectrum of the Stokes coefficients. A proposal for a solution will be discussed. The following steps are important: Expanding the GRACE data with adequate terms of degree one; Valuation of leakage errors because of the limited spectrum. Leakage due to oceanographic signals of the Arctic Ocean are small (< 1%). Leakage errors due to signals on land produces relative errors of basin averages of 8-17%. Beyond that, the largest errors are caused by the coefficients of higher degree. Filtering is an effective method to damp the error signals. In addition to the common filters described in the literature, a filter method, called composite filter, was created. Significant structures from hydrological models can be deteceted in the GRACE data without any other filtering. Only the residual signals should be filtered by using one of the common filters. In comparison to the common filters, the composite filter represents the signal strength, the signal structures, the amplitude and the phase of the saisonal signal on the continents much better. Combining hydrological mass variations from GRACE data with atmospheric data (for example the NCEP reanalysis) the runoff of the four Siberian river systems can be calculated. The validation of the calculated runoff using observations leads to a good agreement (83% for Yenisey and Lena). Furthermore, it is possible to combine the runoff of a river system with measurements of water level and salinity in the Arctic Ocean. The high runoff of the Lena river system in spring is visible in the water level changes in the Laptev sea.
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Lin, Yu-siang, and 林榆翔. "Comparing the GRACE satellite with land hydrology to explore gravity changes in Taiwan." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/99485166256026321989.
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碩士國立中央大學
地球物理研究所
100
In this study we use the GRACE satellite gravity data provided by CSR, of which the GSM version has already had the non-tidal atmosphere and oceans components removed. The highest spherical harmonic degree is 60, corresponding to around 333 kilometers of spatial resolution. We take the point (E121°, N23°45‘) near the central part of Taiwan to represent the whole Taiwan. The GRACE data of gravity changes have relationship with surface water cycle through the surface water balance equation：ΔS/Δt=P-E-R, where ΔS means change in storage converted from GRACE gravity data to the equivalent depth, P means precipitation, E means evapotranspiration, and R means runoff. For P we employ the data of precipitation from the Central Weather Bureau by means of Thiessen Polygons Method. E is modled via the Hamon (1979) algorithm using temperature data. R is obtained from the Water Resources Agency statistics. Comparing between ΔS and P-E-R can help understand the precision of the GRACE Satellite measurement for Taiwan, as well as analyze further the phenomena of surface water cycle in Taiwan. The results show that the correlation is low between the GRACE satellite measurements and the P-E-R. The main reason is Taiwan''s high terrain, steep slope and rapid runoff, resulting rainfall can not stay long on land.
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Cheng, Ying-Hua, and 陳盈樺. "Geocenter and C20 variations derived by satellite altimeters, GRACE and NCEP climate model." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/86316514124500362522.
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碩士國立成功大學
測量及空間資訊學系碩博士班
97
Geocenter variations defined as the position of the Earth’s center of mass (CM) relative to the center of figure (CF) of the Earth’s outer space are caused by mass redistribution like the mass exchange between ocean mass, atmosphere, ice sheets, glaciers, and hydrology. In previous studies, geocenter variations were estimated using Satellite Laser Range (SLR)、Global Positioning System (GPS), or satellite altimeter measurements, but these measurements do not distribute globally and evenly. In addition, some researchers used climate models with unknown uncertainties to estimate geocenter, which causes the errors of estimated geocenter are not assessable. Theoretically, higher degree harmonics do not bias the estimate of degree one because they are orthogonal; however, Lavalle´e et al. [2006] reported that unmodeled higher degree harmonics could actually alias the estimate of geocenter variations. GRACE mission has been successfully and continually providing monthly average observations of the Earth’s gravity field since the satellites were launched in 2002. The observations are represented in form of 2~120 degree spherical harmonic coefficients, but the degree-2 coefficient is currently not well determined. In this study, we estimated geocenter and C20 variations accurately by combining the steric-corrected and loading-corrected altimeter data and GRACE solution to reduce the aliasing of higher degree harmonics to estimate geocenter variations. The annual amplitude of x-, y-, and z-components are 1.2±0.2mm, 2.2±0.2mm, and 2.5±0.3mm respectively. The annual phase of x-, y-, and z-components are 67.8±9o, 337.1±4.7o, 61.1±6.6o respectively. The computational result agrees well with Swenson et al. [2008]. Additionally, compared with GRACE-derived C20, the annual amplitude and phase of the estimated ΔC20 at 1.1×10-10±1.2×10-12 and 35.8±5.8o in this study are much closer to SLR-derived ΔC20. Finally, we join the NCEP climate model (snow, atmospheric pressure, and soil moisture data) to compute geocenter and C20 variations but the estimate is not significant improved because the error of the model may be large and not assessable.
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Tzu-YuanChung and 鐘子淵. "Estimation of Geocenter Variation Using a Combination of GRACE, Satellite Altimetry, and Ocean Models." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/53735444902648484286.
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Wu, I.-Ju, and 吳繹如. "Estimating Antarctica land topography and crustal thickness from GRACE gravity and ICESat altimetry satellite data." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/60709012422462732306.
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碩士國立臺灣大學
地質科學研究所
98
We propose a new method combining GRACE (Gravity Recovery and Climate Experiment) gravity and ICESat (Ice, Cloud, and land Elevation Satellite) altimetry data to estimate the land topography for Antarctica. Antarctica is the fifth-largest continent in the world and about 98% of Antarctica is covered by ice, where in-situ measurements are difficult. Some experimental airborne radar and ground-based radar data have revealed very limited land topography beneath heavy ice sheet. To estimate the land topography for the full coverage of Antarctica, we combine GRACE data that indicate the mass distribution, with data of ICESat laser altimetry that provide high-resolution mapping of ice topography. Our approach is actually based on some geological constraints: assuming uniform densities of the land and ice considering the Airy-type isostasy. In the beginning we construct an initial model for the ice thickness and land topography based on the BEDMAP ice thickness and ICESat data. Thereafter we forward compute the model’s gravity field and compare with the GRACE observed data. Our initial model undergoes the adjustments to improve the fit between modeled results and the observed data. The final results show that the crust thickness is between 17 to 50 kilometer and the ice thickness is between 0 to 4300 m. And final examination is done by comparing our results with previous but sparse observations of ice thickness to reconfirm the reliability of our results. As the gravitational inversion problem is non-unique, our estimating result is just one of all possibilities constrained by available data in optimal way.
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Wang, Cheng-Gi, and 王成機. "Determinations of the Earth's gravity field and its temporal variation from satellite tracking data: case studies for CHAMP and GRACE missions." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/81510444604262529305.
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博士國立交通大學
土木工程系所
93
With the advent of the CHAMP and GRACE satellite missions, satellite gravimetry has opened a new era featuring high spatial resolution and accuracy. These two missions provide continuous satellite tracking data in a high-low（HL-SST） and a low-low satellite-to-satellite tracking（LL-SST） scenario. They are both equipped with accelerometers for determining non-gravitational forces and star-cameras for determining attitudes. For each mission a laser retro-reflector is also mounted to provide additional tracking data. The GRACE mission uses a K-band ranging system to determine ranges and range rates (RR) between the two GRACE satellites at an accuracy of 10 m and 1 m/s, respectively. Precise range-rate rates (RRR) can be derived from RR. The uniqueness and the unprecedented accuracy of CHAMP and GRACE's tracking data have motivated this study, which mainly focuses on methods for efficiently recovering the Earth's gravity field and its temporal variation. A phase method is developed. In this method, GPS phase observations of a low earth orbiter (LEO) are used to compute line-of-sight accelerations between GPS and LEO, which are then used to determine the 3-dimensional accelerations of LEO using precise GPS ephemeris. Accelerations are linear functions of gravity coefficients, which make the least-squares estimation of gravity coefficients very simple in terms of computational effort. This method is efficient and does not require modeling GPS integer ambiguities. However, accelerations other than the Earth's gravity-induced acceleration must be modeled and removed from the phase-determined accelerations. The gravity coefficients recovered from CHAMP by this method agree well with the EGM96 gravity coefficients. Closed, linear expressions between RR or RRR and gravity coefficients are established using a linear orbit perturbation theory. These expressions are based on the concepts that RR is a function of the potential difference between two satellites and RRR is the line-of-sight acceleration. These expressions are used in a least-squares estimation of gravity coefficients from GRACE's RR or RRR. Seven days of simulated data using EGM96 and OSU91A have been used to test the theories and computer programs based on these expressions. A direct acceleration method is employed to determine the time variation of the Earth's gravity field. In this method, the accelerations of LEO are determined by numerical differentiations of the positions of LEO. After removing accelerations other than the Earth's gravity-induced accelerations, linear relations between LEO accelerations and gravity coefficients can be established, as in the phase method. Empirical parameters can be used to model the residual non-Earth-gravity accelerations. The time series of J2 derived from one year of CHAMP data and four months of GRACE data by this method closely resemble the SLR-derived time series of J2. Moreover, one set of normal equations is computed from a 7-day orbit arc. A total of 42 such normal equations from CHAMP data and 33 normal equations from GRACE data are computed. These normal equations are considered uncorrelated and are combined to determine an averaged gravity field. This gravity field yields a geoid model with an accuracy of better 5 mm at a spatial resolution of 1000 km half-wavelength, which is better than those derived from the recent satellite-only EIGEN-1S and EGM96 gravity fields.
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Roesset, Peter Jose. "A simulation study of the use of accelerometer data in the GRACE mission." Thesis, 2003. http://hdl.handle.net/2152/888.
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Roesset, Peter Jose Tapley Bryon D. "A simulation study of the use of accelerometer data in the GRACE mission." 2003. http://wwwlib.umi.com/cr/utexas/fullcit?p3122783.
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Seo, Ki-weon. "Hydrological applications of gravity recovery and climate experiment (GRACE)." Thesis, 2005. http://www.lib.utexas.edu/etd/d/2005/seok61021/seok61021.pdf#page=3.
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Seo, Ki-weon Wilson Clark R. "Hydrological applications of gravity recovery and climate experiment (GRACE)." 2005. http://repositories.lib.utexas.edu/bitstream/handle/2152/1803/seok61021.pdf.
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Wang, Furun Tapley Byron D. "Study on center of mass calibration and K-band ranging system calibration of the GRACE mission." 2003. http://wwwlib.umi.com/cr/utexas/fullcit?p3120308.
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Ko, Ung Dai 1970. "Analysis of the characteristics of grace dual one-way ranging system." 2008. http://hdl.handle.net/2152/17977.
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The motivation for this research was an improvement of the quality of the Earth’s gravity solutions from the GRACE mission data through an instrument-level study. The objective was a better understanding of the characteristics and sources of the highfrequency noise in the range of (0.02 ~ 0.1 Hz) in the dual one-way ranging (DOWR) and its effect on the gravity solution. For this purpose, the mathematical model of the DOWR observation was derived and the Allan variance was computed to establish an upper bound on the level of frequency instability of the ultra-stable oscillators (USO) to determine their contribution to the high-frequency noise. Because they are dominated by the high-frequency noise, the postfit residuals of the time derivative of the DOWR ranges were also examined to evaluate the contributions of various other factors such as system noise from the microwave signal receiver, external influences, and internal influences. The results indicate that the system noise is the dominant source of the excessive highfrequency noise. As one method of mitigation, a tighter bandwidth filter was applied to the DOWR processing, resulting in modest improvements in gravity solutions.text
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Wang, Furun. "Study on center of mass calibration and K-brand ranging system calibration of the GRACE mission." Thesis, 2003. http://hdl.handle.net/2152/28512.
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The twin Gravity Recovery and Climate Experiment (GRACE) satellites were successfully launched on March 17, 2002. The mission goal is to make significant improvement in current measurements of the Earth’s gravity field. The satellites are linked by a K-band ranging system, which measures the range change due to the gravitational and non-gravitational accelerations. The non-gravitational accelerations can be obtained by transforming the accelerometer measurements into the inertial frame of reference based on the star camera observations, and will be used to separate gravitational effects in the range changes. However, the accelerometer’s proof mass offset from the center of mass of the spacecraft must be minimized and the misalignment between star camera frame and accelerometer frame must be known accurately in order to reduce the accelerometer data error. In addition, the phase center of the K-band horn must be known to make antenna offset corrections to the range and range change data. The objective of the center of mass calibration is to determine the proof mass offset, and then, to use the center of mass trim assembly mechanism to eliminate this offset. The main purpose of the K-band ranging system calibration is to determine the phase center of the K-band antenna, which will be used to adjust the satellite attitude orientations and make the antenna offset corrections to the K-band ranging system phase measurements. Furthermore, this calibration allows the misalignment between star camera frame and accelerometer frame to be determined. The calibration maneuvers have been designed for the real mission. Estimation algorithms have been developed and complete simulations have been performed. Finally, the real calibration data have been processed. Analysis shows that the proof mass offset has been determined better than the requirement value of 0.1 mm and trimmed well below this value. The boresight error of the K-band horn’s phase center has been determined better than 0.3 mrad and the resultant antenna offset correction error of range and range rate will be much less than the system resolution (10[mu]m ,1[mu]m/ s) and the frame misalignment parameters have been determined better than (0.04o ,1[delta] ) . Overall, the goal of calibrations has been successfully achieved.text
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Reubelt, Tilo [Verfasser]. "Harmonische Gravitationsfeldanalyse aus GPS-vermessenen kinematischen Bahnen niedrig fliegender Satelliten vom Typ CHAMP, GRACE und GOCE mit einem hoch auflösenden Beschleunigungsansatz / vorgelegt von Tilo Reubelt." 2009. http://d-nb.info/994003153/34.
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Grobler, Johannes Marthinus. "'n Ondersoek van Afrikaanssprekendes se behoeftes aan Afrikaanse televisieprogramme : 'n gevallestudie." Diss., 2001. http://hdl.handle.net/10500/16883.
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Text in AfrikaansHierdie studie ondersoek die behoeftes van Afrikaanse televisiekykers aan Afrikaanse televisieprogramme te midde van die veranderinge wat sedert demokratisering aan die Suid-Afrikaanse medialandskap plaasvind. Hierdie behoeftes word ondersoek by wyse van 'n gevallestudie ender graad 10-leerders in Pretoria. Die gebruike- en bevredigingsbenadering dien as teoretiese onderbou vir die studie en die invloed van 'n aantal veranderlikes word ondersoek. Hierdie veranderlikes is televisiegerig (inhoud, aanbod en struktuur van Afrikaanse programme), tegnologiegerig (nuwe mediategnologiee socs satelliettelevisie en die Internet) en kykergerig (sosio-kulturele, persoonlike en demografiese faktore). Die studie bevind dat daar 'n verband is tussen hierdie veranderlikes en respondente se behoeftes aan Afrikaanse televisieprogramme. Die studie bevind dat Afrikaanse programme nie respondente se behoeftes bevredig nie. Nuwe mediategnologiee verbreed respondente se sosio-kulturele horlE;onne sodat hulle gemaklik met programme in Engels omgaan. Te midde van die toenemende aanbod van oorsese programme in Engels, neem die behoefte aan Afrikaanse programme af.
This study investigates the need for Afrikaans television programmes among Afrikaans viewers in the changing media environment in South Africa. Needs are studied by means of a case study among grade 10 learners in Pretoria. The uses and gratifications approach serves as the theoretical framework of the study and a number of variables are investigated. These variables are television driven (supply, content and structure), technology driven (new media technologies such as satellite television and the Internet) and viewer driven (socio-cultural, personal and demographic factors). The study finds that there is a connection between these variables and the need for Afrikaans programmes among respondents. The supply, content and structure of Afrikaans programmes do not gratify respondents' needs. New media technologies broaden respondents' socio-cultural horizons, enabling them to comfortably watch English programmes. Amidst the increasing supply of overseas programmes in English, the need for Afrikaans programmes is diminishing
Communication Science
M. A. (Kommunikasiekunde)