Difference between pages "IC SG4" and "IC SG5"

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<big>'''JSG 0.13: Integral equations of potential theory for continuation and transformation of classical and new gravitational observables'''</big>
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<big>'''Satellite gravity theory'''</big>
  
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Chair:''Michal Šprlák (Czech Republic)''<br>
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Chair: ''T. Mayer-Gürr (Germany)''<br>
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Affiliation:''Commission 2 and GGOS''
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Affiliation: ''Comm. 2''
  
 
__TOC__
 
__TOC__
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===Introduction===
 
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The description of the Earth's gravitational field and its temporal variations belongs to fundamental pillars of modern geodesy. The accurate knowledge of the global gravitational field is important in many applications including precise positioning, metrology, geophysics, geodynamics, oceanography, hydrology, cryospheric and other geosciences. Various observation techniques for collecting gravitational data have been invented based on terrestrial, marine, airborne and more recently, satellite sensors. On the other hand, different parametrization methods of the gravitational field were established in geodesy, however, with many unobservable parameters. For this reason, the geodetic science has traditionally been formulating various gravitational parameter transformations, including those based on solving boundary/initial value problems of potential theory, through Fredholm's integral equations.
 
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Traditionally, Stokes’s, Vening-Meinesz’s and Hotine’s integrals have been of interest in geodesy as they accommodated geodetic applications. In recent history, new geodetic integral transformations were formulated. This effort was mainly initiated by new gravitational observables that became gradually available to geodesists with the advent of precise GNSS (Global Navigation Satellite Systems) positioning, satellite altimetry and aerial gravimetry/gradiometry.  The family of integral transformations has enormously been extended with satellite-to-satellite tracking and satellite gradiometric data available from recent gravity-dedicated satellite missions.
 
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Besides numerous efforts in developing integral equations to cover new observables in geodesy, many aspects of integral equations remain challenging. This study group aims for systematic treatment of integral transformation in geodesy, as many formulations have been performed by making use of various approaches. Many solutions are based on spherical approximation that cannot be justified for globally distributed satellite data and with respect to requirements of various data users requiring gravitational data to be distributed the reference ellipsoid or at constant geodetic altitude. On the other hand, the integral equations in spherical approximation possess symmetric properties that allow for studying their spatial and spectral properties; they also motivate for adopting a generalized notation. New numerically efficient, stable and accurate methods for upward/downward continuation, comparison, validation, transformation, combination and/or for interpretation of gravitational data are also of high interest with increasing availability of large amounts of new data.
 
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===Objectives===
 
===Objectives===
  
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* To consider different types of gravitational data, i.e., terrestrial, aerial and satellite, available today and to formulate their mathematical relation to the gravitational potential.
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* Gravity field estimation
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* To study mathematical properties of differential operators in spherical and Jacobi ellipsoidal coordinates, which relate various functionals of the gravitational potential.
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** Perturbation techniques versus in-situ measurements and new aproaches like short-arc integration, energy balance and so on.
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* To complete the family of integral equations relating various types of current and foreseen gravitational data and to derive corresponding spherical and ellipsoidal Green’s functions.
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** Computational problems related to the huge quantities of data. Algorithms to divide the computational tasks to run on massive parallel systems.
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* To study accurate and numerically stable methods for upward/downward continuation of gravitational field parameters.
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* Noise and error treatment
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* To investigate optimal combination techniques of heterogeneous gravitational field observables for gravitational field modelling at all scales.
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** Estimating the variance-covariance matrices of the observations, filtering techniques.
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* To investigate conditionality as well as spatial and spectral properties of linear operators based on discretized integral equations.
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** Integrated analysis of different sensors featuring individual noise characteristics (like Accelerometer and K-band sensor in case of GRACE), calibration of instruments (internal and external).
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* To classify integral transformations and to propose suitable generalized notation for a variety of classical and new integral equations in geodesy.
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** A-posteriori variance-covariance matrices, error propagation, validation.
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** Space-time resolution, de-aliasing. Which signals can be estimated and which must be modeled?
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* Gravity field modeling
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** Choice of basis functions in time and space (with respect to applications in hydrology, oceanography).
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** Global and regional modeling, modeling in terms of gravity sources (mass variations).
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** Reference systems and datum problems (origin, orientation, static and temporal datum systems for gravity field changes).
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* Aspects of data combination
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** Combination of the satellite gravity missions (CHAMP, GRACE and GOCE) with terrestrial and aerial gravity information.
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** Combination at the data level versus combination of results.
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** A-priori information from non-gravity data such as changes in the geometry of the Earth and its rotation.
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** Unified approaches: Joint analysis of gravity field observations, Earth rotation, and geometry changes.
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* Future satellite missions
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** Theory of new observation types and intruments.
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** Formation flights. Investigation into stability of satellite formations and their sensitivity to aliasing errors.
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** Follow-on gravity field missions.
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** Orbit determination: theory, perturbation techniques, stability problems.
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** Challenges caused by the inceasing accuracy of the observations: integration techniques, numerical problems due to limited digits in computation.
  
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===Program of Activities===
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===Program of activities===
  
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* Presenting research results at major international geodetic and geophysical conferences, meetings and workshops.
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* Email:<br /> Internal email discussions
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* Organizing a session at the forthcoming Hotine-Marussi Symposium 2017.
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* Meeting:<br /> Organization of working group meeting at larger meetings.
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* Cooperating with related IAG Commissions and GGOS.
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* Website:<br /> Launch of a website for communications, informations and links to data sources
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* Monitoring activities of JGS members as well as other scientists related to the scope of JGS activities.
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* Simulation data:<br /> Assemble of a simulated data set with orbits, background models and artificial noise. This data set serves to test new algorithms and make different aproaches comparable.
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* Providing bibliographic list of relevant publications from different disciplines in the area of JSG interest.
 
  
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===Members===
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===Membership===
  
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'' '''Michal Šprlák (Czech Republic), chair''' <br /> Alireza Ardalan (Iran) <br /> Mehdi Eshagh (Sweden) <br /> Will Featherstone (Australia) <br /> Ismael Foroughi (Canada) <br /> Petr Holota (Czech Republic) <br /> Juraj Janák (Slovakia) <br /> Otakar Nesvadba (Czech Republic) <br /> Pavel Novák (Czech Republic) <br /> Martin Pitoňák (Czech Republic) <br /> Robert Tenzer (China) <br /> Guyla Tóth (Hungary) <br />''
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'' '''Torsten Mayer-Guerr (Germany)'''<br /> Oliver Baur (Germany)<br /> Wolfgang Bosch (Germany)<br /> Pavel Ditmar (Netherlands)<br /> Thomas Gruber (Germany)<br /> Shin-Chan Han (USA)<br /> Michael Kern (Netherlands)<br /> Juergen Kusche (Germany)<br /> Michael Schmidt (Germany)<br /> Roland Schmidt (Germany)<br /> Roland Pail (Austria)<br /> Insa Wolf (Germany)<br />''

Revision as of 13:52, 22 April 2008

Satellite gravity theory

Chair: T. Mayer-Gürr (Germany)
Affiliation: Comm. 2

Objectives

  • Gravity field estimation
    • Perturbation techniques versus in-situ measurements and new aproaches like short-arc integration, energy balance and so on.
    • Computational problems related to the huge quantities of data. Algorithms to divide the computational tasks to run on massive parallel systems.
  • Noise and error treatment
    • Estimating the variance-covariance matrices of the observations, filtering techniques.
    • Integrated analysis of different sensors featuring individual noise characteristics (like Accelerometer and K-band sensor in case of GRACE), calibration of instruments (internal and external).
    • A-posteriori variance-covariance matrices, error propagation, validation.
    • Space-time resolution, de-aliasing. Which signals can be estimated and which must be modeled?
  • Gravity field modeling
    • Choice of basis functions in time and space (with respect to applications in hydrology, oceanography).
    • Global and regional modeling, modeling in terms of gravity sources (mass variations).
    • Reference systems and datum problems (origin, orientation, static and temporal datum systems for gravity field changes).
  • Aspects of data combination
    • Combination of the satellite gravity missions (CHAMP, GRACE and GOCE) with terrestrial and aerial gravity information.
    • Combination at the data level versus combination of results.
    • A-priori information from non-gravity data such as changes in the geometry of the Earth and its rotation.
    • Unified approaches: Joint analysis of gravity field observations, Earth rotation, and geometry changes.
  • Future satellite missions
    • Theory of new observation types and intruments.
    • Formation flights. Investigation into stability of satellite formations and their sensitivity to aliasing errors.
    • Follow-on gravity field missions.
    • Orbit determination: theory, perturbation techniques, stability problems.
    • Challenges caused by the inceasing accuracy of the observations: integration techniques, numerical problems due to limited digits in computation.

Program of activities

  • Email:
    Internal email discussions
  • Meeting:
    Organization of working group meeting at larger meetings.
  • Website:
    Launch of a website for communications, informations and links to data sources
  • Simulation data:
    Assemble of a simulated data set with orbits, background models and artificial noise. This data set serves to test new algorithms and make different aproaches comparable.

Membership

Torsten Mayer-Guerr (Germany)
Oliver Baur (Germany)
Wolfgang Bosch (Germany)
Pavel Ditmar (Netherlands)
Thomas Gruber (Germany)
Shin-Chan Han (USA)
Michael Kern (Netherlands)
Juergen Kusche (Germany)
Michael Schmidt (Germany)
Roland Schmidt (Germany)
Roland Pail (Austria)
Insa Wolf (Germany)

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