Difference between revisions of "JSG T.28"

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<big>'''JSG 0.15: Regional geoid/quasi-geoid modelling – Theoretical framework for the sub-centimetre accuracy'''</big>
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<big>'''JSG T.28: Forward gravity field modelling of known mass distributions'''</big>
  
Chairs: ''Jianliang Huang (Canada)''<br />
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Chairs: ''Dimitrios Tsoulis (Greece)''<br />
Affiliation: ''Comm. 2 and GGOS''
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Affiliation: ''Commissions 2 and 3, GGOS''
  
 
__TOC__
 
__TOC__
  
===Problem statement===
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===Introduction===
  
A theoretical framework for the regional geoid/quasi-geoid modelling is a conceptual structure to solve a geodetic boundary value problem regionally. It is a physically sound integration of a set of coherent definitions, physical models and constants, geodetic reference systems and mathematical equations. Current frameworks are designed to solve one of the two geodetic boundary value problems: Stokes’s and Molodensky’s. These frameworks were originally established and subsequently refined for many decades to get the best accuracy of the geoid/quasi-geoid model. The regional geoid/quasi-geoid model can now be determined with an accuracy of a few centimeters in a number of regions in the world, and has been adopted to define new vertical datum replacing the spirit-leveling networks in New Zealand and Canada. More and more countries are modernizing their existing height systems with the geoid-based datum. Yet the geoid model still needs further improvement to match the accuracy of the GNSS-based heightening. This requires the theory and its numerical realization, to be of sub-centimeter accuracy, and the availability of adequate data.
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he geometrical definition of the shape and numerical evaluation of the corresponding gravity signal of any given mass distribution express a central theme in gravity field modelling. Involving different theoretical and computational aspects of the potential field theory and including the element of interpreting the computed signal by comparing it with the observed gravity field, the specific research topic determines a characteristic interface between geodesy and geophysics.
  
Regional geoid/quasi-geoid modelling often involves the combination of satellite, airborne, terrestrial (shipborne and land) gravity data through the remove-compute-restore Stokes method and the least-squares collocation. Satellite gravity data from recent gravity missions (GRACE and GOCE) enable to model the geoid components with an accuracy of 1-2 cm at the spatial resolution of 100 km. Airborne gravity data are covering more regions with a variety of accuracies and spatial resolutions such as the US GRAV-D project. They often overlap with terrestrial gravity data, which are still unique in determining the high-degree geoid components. It can be foreseen that gravity data coverage will extend everywhere over lands, in particular, airborne data, in the near future.  Furthermore, the digital elevation models required for the gravity reduction have achieved global coverage with redundancy.  A pressing question to answer is if these data are sufficiently accurate for the sub-centimeter geoid/quasi-geoid determination. This study group focuses on refining and establishing if necessary the theoretical frameworks of the sub-centimeter geoid/quasi-geoid.  
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Theoretical and methodological aspects of mass modelling concern a wide range of applications, from computing gravity anomalies and geoid to reducing satellite gradiometry data or solving an extended family of integral equations of the potential theory. Directly linked to real mass density distributions in the Earth's interior, the problem of computing the potential function of given mass density distributions and its spatial derivatives up to higher orders defines the core of forward gravity field modelling, while also constituting an integral part of an inverse modelling flowchart in geophysics.
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The availability of an abundance of terrestrial and satellite data of global coverage and increasing spatial resolution provides a challenging framework for revisiting known theoretical aspects and especially investigating computational limits and possibilities of forward gravity modelling induced by known mass distributions. Satellite observations provide global grids of gravity related quantities at satellite altitudes, global crustal databases offer detailed layered information of the shape and consistency of the Earth's crust, while satellite methods produce digital elevation models that represent a continental part of the topographic surface with unprecedented resolution.
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The current datasets enable the consideration of several theoretical, methodological and computational aspects of forward gravity field modelling. For instance, dense digital elevation models provide a unique input dataset that challenges the evaluation of precise terrain effects, especially in areas of very steep terrain. At the same time and due to the availability of new data, the complete theoretical framework that evaluates the gravity effect of a given distribution using analytical, numerical or spectral techniques emerges again at the forefront of research, examining both ideal bodies and real distributions. Finally, the existence of detailed information of the structure in the Earth's interior provides an opportunity to revisit synthetic Earth reference models by computing the actual gravity effect induced by these distributions and validate it against the observed gravity signal obtained by the available gravity field models.
  
 
===Objectives===
 
===Objectives===
  
The theoretical frameworks of the sub-centimeter geoid/quasi-geoid consist of, but are not limited to, the following components to study:
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* Examine new theoretical developments (numerical, analytical or spectral) in expressing the gravity signal of ideal geometric distributions.
* Physical constant GM
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* Perform validation studies of precise terrain effects over rugged mountainous topography.
* W0 convention and changes
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* Compute the gravity effect of structures in the Earth's interior and embed this effort in the frame of a synthetic reference Earth model.
* Geo-center convention and motion with respect to the International Terrestrial Reference Frame (ITRF)
 
* Geodetic Reference Systems
 
* Proper formulation of the geodetic boundary value problem
 
* Nonlinear solution of the formulated geodetic boundary value problem
 
* Data type, distribution and quality requirements
 
* Data interpolation and extrapolation methods
 
* Gravity reduction including downward or upward continuation from observation points down or up to the geoid, in particular over mountainous regions, polar glaciers and ice caps
 
* Anomalous topographic mass density effect on the geoid model
 
* Spectral combination of different types of gravity data
 
* Transformation between the geoid and quasi-geoid models
 
* The time-variable geoid/quasi-geoid change modelling
 
* Estimation of the geoid/quasi-geoid model inaccuracies
 
* Independent validation of geoid/quasi-geoid models
 
* Applications of new tools such as the radial basis functions
 
  
 
===Program of activities===
 
===Program of activities===
  
* The study group achieves its objectives through organizing splinter meetings in coincidence with major IAG conferences and workshops if possible.
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* Participation in forthcoming IAG conferences with splinter meetings and proposed sessions.
* Circulating and sharing progress reports, papers and presentations.
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* Preparation of joint publications with JSG members.
* Presenting and publishing papers in the IAG symposia and scientific journals.  
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* Organization of a session at the Hotine-Marussi Symposium 2022.
  
 
===Members===
 
===Members===
 
   
 
   
'' '''Jianliang Huang (Canada), chair''' <br /> '''Yan Ming Wang (USA), vice-chair''' <br /> Riccardo Barzaghi (Italy) <br /> Heiner Denker (Germany) <br /> Will Featherstone (Australia) <br /> René Forsberg (Denmark) <br /> Christian Gerlach (Germany) <br /> Christian Hirt (Germany) <br /> Urs Marti (Switzerland) <br /> Petr Vaníček (Canada) <br />''
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'' '''Dimitrios Tsoulis (Greece), chair''' <br /> Carla Braitenberg (Italy) <br /> Christian Gerlach (Germany) <br /> Ropesh Goyal (India) <br /> Olivier Jamet (France) <br /> Michael Kuhn (Australia) <br /> Pavel Novák (Czech Republic) <br /> Konstantinos Patlakis (Greece) <br /> Daniele Sampietro (Italy) <br /> Matej Varga (Croatia) <br /> Jérôme Verdun (France) <br />''

Latest revision as of 10:50, 10 June 2020

JSG T.28: Forward gravity field modelling of known mass distributions

Chairs: Dimitrios Tsoulis (Greece)
Affiliation: Commissions 2 and 3, GGOS

Introduction

he geometrical definition of the shape and numerical evaluation of the corresponding gravity signal of any given mass distribution express a central theme in gravity field modelling. Involving different theoretical and computational aspects of the potential field theory and including the element of interpreting the computed signal by comparing it with the observed gravity field, the specific research topic determines a characteristic interface between geodesy and geophysics.

Theoretical and methodological aspects of mass modelling concern a wide range of applications, from computing gravity anomalies and geoid to reducing satellite gradiometry data or solving an extended family of integral equations of the potential theory. Directly linked to real mass density distributions in the Earth's interior, the problem of computing the potential function of given mass density distributions and its spatial derivatives up to higher orders defines the core of forward gravity field modelling, while also constituting an integral part of an inverse modelling flowchart in geophysics.

The availability of an abundance of terrestrial and satellite data of global coverage and increasing spatial resolution provides a challenging framework for revisiting known theoretical aspects and especially investigating computational limits and possibilities of forward gravity modelling induced by known mass distributions. Satellite observations provide global grids of gravity related quantities at satellite altitudes, global crustal databases offer detailed layered information of the shape and consistency of the Earth's crust, while satellite methods produce digital elevation models that represent a continental part of the topographic surface with unprecedented resolution.

The current datasets enable the consideration of several theoretical, methodological and computational aspects of forward gravity field modelling. For instance, dense digital elevation models provide a unique input dataset that challenges the evaluation of precise terrain effects, especially in areas of very steep terrain. At the same time and due to the availability of new data, the complete theoretical framework that evaluates the gravity effect of a given distribution using analytical, numerical or spectral techniques emerges again at the forefront of research, examining both ideal bodies and real distributions. Finally, the existence of detailed information of the structure in the Earth's interior provides an opportunity to revisit synthetic Earth reference models by computing the actual gravity effect induced by these distributions and validate it against the observed gravity signal obtained by the available gravity field models.

Objectives

  • Examine new theoretical developments (numerical, analytical or spectral) in expressing the gravity signal of ideal geometric distributions.
  • Perform validation studies of precise terrain effects over rugged mountainous topography.
  • Compute the gravity effect of structures in the Earth's interior and embed this effort in the frame of a synthetic reference Earth model.

Program of activities

  • Participation in forthcoming IAG conferences with splinter meetings and proposed sessions.
  • Preparation of joint publications with JSG members.
  • Organization of a session at the Hotine-Marussi Symposium 2022.

Members

Dimitrios Tsoulis (Greece), chair
Carla Braitenberg (Italy)
Christian Gerlach (Germany)
Ropesh Goyal (India)
Olivier Jamet (France)
Michael Kuhn (Australia)
Pavel Novák (Czech Republic)
Konstantinos Patlakis (Greece)
Daniele Sampietro (Italy)
Matej Varga (Croatia)
Jérôme Verdun (France)