At the beginning of the new millennium, the idea of measuring localized functionals of the gravity potential along orbit using a single satellite with an onboard gravity gradiometer was proposed and successfully implemented in the concept of the GOCE (Gravity field and steady Ocean Circulation Explorer) mission. It was the first Earth Explorer mission of the European Space Agency (ESA) and delivered plenty of data to the scientific communities and the space agencies and brought our understanding of the Earth gravity field to a new level. The main innovative instrument of this mission was based on the technology of the electrostatic accelerometers. Such classical sensors have found various applications for inertial and gravity sensing payloads. Recently, worldwide laboratories and research institutes have proposed the idea of exploiting cold atom quantum sensors to increase the performance of inertial (gravity) measurements for future gravity missions. In this thesis work, the new mission concept will be explained and simulations will be presented to show how, using a new and highly improved gradiometer based on cold atom interferometer, the performance of GOCE could be improved over a larger measurement bandwidth. Chapter 1 includes the theoretical background of the Earth gravity field and the main principles of gravity field determination. The first section introduces the terms widely used in geodesy, while the next sections explain the measurement techniques. Chapter 2 is dedicated to satellite geodesy, introducing different concepts for gravity field determination from space. Different satellite gravity missions are described, which exploited different concepts and were launched for measuring and monitoring the Earth gravity field. Also, a summary of recent global gravity field models derived from these missions is given to outline the actual knowledge of the Earth gravity field. Chapter 3 describes the main idea of an innovative gradiometer exploiting ultra-cold atom technology. To evaluate the performance of a cold atom gradiometer, the instrument concept is presented, as well as further technological development required to achieve a better performance than the electrostatic gradiometer. Chapter 4 explains the data analysis method exploited for this work, namely the space-wise approach, applied to the simulated data. The simulated observables are the second derivatives of the gravitational potential at given points along the orbit in a given direction (e.g., the radial one). The unknowns are the spherical harmonic coefficients, retrieved by applying the space-wise approach. In this way, data that are close in space but far in time can be filtered together thanks to an intermediate gridding step that is typically implemented by least-squares collocation. Chapter 5 and Chapter 6 present the simulations and data analysis performed for two studies of future gravity missions, the so-called MOCASS and CAI studies, in which the onboard gradiometer is based on cold atom interferometry. From the measurement principle point-of-view, such new mission concepts can be considered as a GOCE follow-on, as the on-board gradiometer measures the second derivatives of the gravitational potential. To evaluate the performance of the innovative gradiometer, different scenarios have been set up for numerical simulations and the results will be explained and compared with those of the GOCE and GRACE (Gravity Recovery and Climate Experiment) missions.
Agli albori del nuovo millennio, l’idea di misurare funzionali del campo gravitazionale terrestre localizzati lungo orbita usando un singolo satellite con un gradiometro `e stata proposta e implementata con successo nella missione GOCE (Gravity field and steady Ocean Circulation Explorer). Questa `e stata la prima missione Earth Explorer dell’Agenzia Spaziale Europea (ESA) e ha fornito molti dati alla Comunit`a scientifica e alle agenzie spaziali, portando a un nuovo livello la conoscenza della la gravit`a terrestre. Il principale strumento di questa missione era basato sulla tecnologia degli accelerometri elettrostatici. Tali sensori sono stati sfruttati con successo per payload sia inerziali che gravit`a. Di recente, diversi laboratori e istituti di ricerca in tutto il mondo hanno proposto l’idea di sfruttare i sensori quantistici ad atomi freddoi per aumentare le prestazioni di misure inerziali (di gravit`a) per future missioni gravitazionali. Questo concetto di missione, che utilizza un nuovo e avanzato gradiometro basato su un interferometro ad atomi freddi, potrebbe migliorare le prestazioni di GOCE garantendo anche una pi`u ampia banda spettrale di misura. Il primo capitolo include la teoria di base relative al campo gravitazionale terrestre e i principi generali riguardanti la determinazione del campo gravitazionale. La prima sezione introduce i termini ampiamente usati in geodesia, mentre le sezioni successive spiegano le tecniche di misurazione. Il secondo capitolo `e dedicato alla geodesia satellitare, e introduce diversi concetti sulla determinazione del campo gravitazionale dallo spazio. Verranno descritte alcune missioni gravitazionali, basate su diversi concetti e aventi lo scopo di misurare e monitorare il campo gravitazionale terrestre. Inoltre, sar`a presentato un riepilogo dei recenti modelli globali di campo gravitazionale derivati da queste missioni al fine di delineare l’effettiva conoscenza del campo gravitazionale terrestre. Il terzo capitolo descrive l’idea alla base di un innovativo gradiometro che sfrutta la tecnologia ad atomi ultra-freddi. Per valutare le prestazioni di tale gradiometro, descriveremo il funzionamento dello strumento e l’ulteriore sviluppo tecnico necessario per ottenere una migliore prestazione rispetto al gradiometro elettrostatico. Il quarto capitolo spiega il metodo di analisi dati sfruttato per questo lavoro, chiamato “approccio space-wise” e applicato ai dati simulati. Le osservabili simulate sono le derivate seconde del campo gravitazionale in determinati punti dell’orbita in una data direzione (ad esempio, quella radiale). Le incognite sono i coefficienti armonici sferici, stimati grazie all’applicazione dell’approccio spacewise. In questo modo, i dati che sono vicini nello spazio ma lontani nel tempo possono essere filtrati insieme grazie alla stima intermedia di una griglia di valori che viene di solito ottenuta tramite un approccio di collocazione. Il capitolo 5 e il capitolo 6 presentano le simulazioni e l’analisi dei dati eseguite per due studi di future missioni gravitazionali, i cosiddetti studi MOCASS e CAI, in cui il gradiometro a bordo `e rappresentato da un interferometro ad atomi freddi. In merito al principio di misurazione, tali nuovi concetti di missione possono essere considerati come un seguito del GOCE, poich´e il gradiometro di bordo misura le derivate seconde del campo gravitazionale. Per valutare le prestazioni innovative del gradiometro, sono stati creati diversi scenari per le simulazioni numeriche e i risultati saranno presentati e confrontati con quelli delle missioni GOCE e GRACE (Gravity Recovery and Climate Experiment).
Gravity field recovery from gradiometric missions based on cold atom technology
BATSUKH, KHULAN
2019/2020
Abstract
At the beginning of the new millennium, the idea of measuring localized functionals of the gravity potential along orbit using a single satellite with an onboard gravity gradiometer was proposed and successfully implemented in the concept of the GOCE (Gravity field and steady Ocean Circulation Explorer) mission. It was the first Earth Explorer mission of the European Space Agency (ESA) and delivered plenty of data to the scientific communities and the space agencies and brought our understanding of the Earth gravity field to a new level. The main innovative instrument of this mission was based on the technology of the electrostatic accelerometers. Such classical sensors have found various applications for inertial and gravity sensing payloads. Recently, worldwide laboratories and research institutes have proposed the idea of exploiting cold atom quantum sensors to increase the performance of inertial (gravity) measurements for future gravity missions. In this thesis work, the new mission concept will be explained and simulations will be presented to show how, using a new and highly improved gradiometer based on cold atom interferometer, the performance of GOCE could be improved over a larger measurement bandwidth. Chapter 1 includes the theoretical background of the Earth gravity field and the main principles of gravity field determination. The first section introduces the terms widely used in geodesy, while the next sections explain the measurement techniques. Chapter 2 is dedicated to satellite geodesy, introducing different concepts for gravity field determination from space. Different satellite gravity missions are described, which exploited different concepts and were launched for measuring and monitoring the Earth gravity field. Also, a summary of recent global gravity field models derived from these missions is given to outline the actual knowledge of the Earth gravity field. Chapter 3 describes the main idea of an innovative gradiometer exploiting ultra-cold atom technology. To evaluate the performance of a cold atom gradiometer, the instrument concept is presented, as well as further technological development required to achieve a better performance than the electrostatic gradiometer. Chapter 4 explains the data analysis method exploited for this work, namely the space-wise approach, applied to the simulated data. The simulated observables are the second derivatives of the gravitational potential at given points along the orbit in a given direction (e.g., the radial one). The unknowns are the spherical harmonic coefficients, retrieved by applying the space-wise approach. In this way, data that are close in space but far in time can be filtered together thanks to an intermediate gridding step that is typically implemented by least-squares collocation. Chapter 5 and Chapter 6 present the simulations and data analysis performed for two studies of future gravity missions, the so-called MOCASS and CAI studies, in which the onboard gradiometer is based on cold atom interferometry. From the measurement principle point-of-view, such new mission concepts can be considered as a GOCE follow-on, as the on-board gradiometer measures the second derivatives of the gravitational potential. To evaluate the performance of the innovative gradiometer, different scenarios have been set up for numerical simulations and the results will be explained and compared with those of the GOCE and GRACE (Gravity Recovery and Climate Experiment) missions.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/173574