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Gravity field processing towards LL-SST satellite missions / Ilias Daras (2016)  

Public Titre : Gravity field processing towards LL-SST satellite missions Type de document : Thèse/HDR Auteurs : Ilias Daras, Auteur ; Roland Pail, Directeur de thèse Editeur : Munich : Bayerische Akademie der Wissenschaften Année de publication : 2016 Collection : DGK - C, ISSN 0065-5325 num. 770 Importance : 153 p. ISBN/ISSN/EAN : 978-3-7696-5182-9 Note générale : bibliographie PhD Dissertation Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] accéléromètre [Termes IGN] champ de pesanteur terrestre [Termes IGN] crénelage [Termes IGN] filtrage du bruit [Termes IGN] gravimétrie spatiale [Termes IGN] interféromètre au laser [Termes IGN] poursuite de satellite [Termes IGN] résidu [Termes IGN] satellite d'observation de la Terre Résumé : (auteur) This study focuses on important aspects concerning gravity field processing of future LL-SST [Low-Low Satellite-to-Satellite Tracking] satellite missions. Closed-loop simulations taking into account error models of new generation instrument technology are used to estimate the gravity field accuracy that future missions could provide. Limiting factors are identified, and methods for their treatment are developed. The contribution of all error sources to the error budget is analyzed. It is shown that gravity field processing with double precision may be a limiting factor for exploiting the nm-level accuracy of a laser interferometer. An enhanced numerical precision processing scheme is proposed instead, where double and quadruple precision is used in different parts of the processing chain. It is demonstrated that processing with enhanced precision can efficiently handle laser measurements and take full advantage of their accuracy, while keeping the computational times within reasonable levels. However, error sources of considerably larger impact are expected to affect future missions, with the accelerometer instrument noise and temporal aliasing effects being the most significant ones. The effect of time-correlated noise such as the one present in accelerometer measurements, can be efficiently handled by frequency dependent data weighting. Residual time series that contain the effect of system errors and propagated accelerometer and laser noise, is considered as a noise realization with stationary stochastic properties. The weight matrix is constructed from the auto-correlation functions of these residuals. Applying the weight matrix to a noise case considering all error sources leads to reduction of the error level over the complete spectral bandwidth. Co-estimation of empirical accelerations does not show the same efficiency in reducing the propagated noise with the applied processing strategy. Temporal aliasing effects are reduced essentially by adding a second pair of satellites at an inclined orbit. Compared to a GRACE-type near-polar pair, such a Bender-type constellation delivers solutions with major improvements in terms of de-aliasing potential and recovery performance. When the integrated effect of all geophysical processes is recovered, the maximum spatial resolution of 11-day solutions can be increased from 715 to 315 km half-wavelength. A further reduction of temporal aliasing errors is possible by co-parameterizing low resolution gravity fields at short time intervals, together with the higher resolution gravity field which is sampled at a longer time interval. One day was found to be the optimal sampling period for reducing the error levels in the solutions. A uniform sampling at the co-parameterized short periods, is a prerequisite for an efficient reduction of aliasing errors. High frequency atmospheric signals are captured by daily solutions to a large extent. Hence co-parameterization at daily basis results in significant reduction of aliasing caused by their under-sampling. This enables future gravity satellite missions to deliver the complete spectrum of Earth's geophysical processes. The corresponding by-products of daily gravity field solutions are expected to be very useful to atmospheric science and open doors to new fields of application. Note de contenu : 1. Introduction 1.1. Background 1.2. Motivation and objectives of this study 1.3. Outline 2. Earth's gravity field determination form satellite observations 2.1. Pertubing forces acting on a satellite 2.2. Geopotential and its functionals 2.3. Dedicated gravity satellite missions 2.4. Concepts for future satellite gravity missions 3. Description of the simulation environment for the gravity fields recovery 3.1. Outline of the simulation environment 3.2. Coordinate and time systems 3.3. Simulation if the satellite orbits 3.4. Functional model 3.5. Formulation of the NEQ system 3.6. Solution of the NEQ system 4. Design aspects and error budget of future dedicated gravity satellite missions 4.1. Orbit design 4.2. Satellite formation flights 4.3. Selected orbits for the simulations 4.4. Science and mission requirements 4.5. Noise models for the performance of the instruments 4.6. Error budget analysis 7. Treatment of temporal aliasing effects 7.1. Temporal aliasing for NGGLs 7.2. Co-parameterization of low spatial resolution gravity fiels solutions at higher frequencies 7.3. Retrieval content of NGGM gravity fiels solutions 8. Conclusions Numéro de notice : 19791 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Note de thèse : PhD Dissertation : Geodesy : Stuttgart : 2016 DOI : sans En ligne : http://nbn-resolving.de/urn:nbn:de:bvb:91-diss-20160211-1279854-1-3 Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=85011

Gravity field processing with enhanced numerical precision for LL-SST missions / Ilias Daras in Journal of geodesy, vol 89 n° 2 (February 2015)  

Public [article]  inJournal of geodesy > vol 89 n° 2 (February 2015) . - pp 99 - 110 Titre : Gravity field processing with enhanced numerical precision for LL-SST missions Type de document : Article/Communication Auteurs : Ilias Daras, Auteur ; Roland Pail, Auteur ; Michael Murböck, Auteur ; Wei Yong Yi, Auteur Année de publication : 2015 Article en page(s) : pp 99 - 110 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] capteur spatial [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GRACE [Termes IGN] interféromètre au laser [Termes IGN] orbitographie par GNSS [Termes IGN] poursuite de satellite [Termes IGN] précision absolue [Termes IGN] test de performance Résumé : (auteur) On their way to meet the augmenting demands of the Earth system user community concerning accuracies of temporal gravity field models, future gravity missions of low-low satellite-to-satellite tracking (LL-SST) type are expected to fly at optimized formations and make use of the latest technological achievements regarding the on-board sensor accuracies. Concerning the main measuring unit of an LL-SST type gravity mission, the inter-satellite measuring instrument, a much more precise interferometric laser ranging system is planned to succeed the K-band ranging system used by the Gravity Recovery and Climate Experiment (GRACE) mission. This study focuses on investigations concerning the potential performance of new generation sensors such as the laser interferometer within the gravity field processing chain. The sufficiency of current gravity field processing accuracies is tested against the new sensor requirements, via full-scale closed-loop numerical simulations of a GRACE Follow-On configuration scenario. Each part of the processing is validated separately with special emphasis on numerical errors and their impact on gravity field solutions. It is demonstrated that gravity field processing with double precision may be a limiting factor for taking full advantage of the laser interferometer’s accuracy. Instead, a hybrid processing scheme of enhanced precision is introduced, which uses double and quadruple precision in different parts of the processing chain, leading to system accuracies of only 17 nm in terms of geoid height reconstruction errors. Simulation results demonstrate the ability of enhanced precision processing to minimize the processing errors and thus exploit the full precision of a laser interferometer, when at the same time the computational times are kept within reasonable levels. Numéro de notice : A2015-331 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-014-0764-2 Date de publication en ligne : 18/10/2014 En ligne : https://doi.org/10.1007/s00190-014-0764-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=76656 [article]