Difference between revisions of "IC SG6"

From Icctwiki
Jump to: navigation, search
 
(4 intermediate revisions by the same user not shown)
Line 1: Line 1:
−
<big>'''JSG 0.6: Applicability of current GRACE solution strategies to the next generation of inter-satellite range observations'''</big>
+
<big>'''JSG 0.15: Regional geoid/quasi-geoid modelling – Theoretical framework for the sub-centimetre accuracy'''</big>
  
−
Chairs: ''M. Weigelt (Germany), A. Jäggi (Switzerland)''<br />
+
Chairs: ''Jianliang Huang (Canada)''<br />
−
Affiliation: ''Comm. 2''
+
Affiliation: ''Comm. 2 and GGOS''
  
 
__TOC__
 
__TOC__
Line 8: Line 8:
 
===Problem statement===
 
===Problem statement===
  
−
The GRACE-mission (Tapley et al., 2004b) proved to be one of the most important satellite missions in recent times as it enabled the recovery of the static gravity field with unprecedented accuracy and, for the first time, the determination of temporal variations on a monthly (and shorter) basis. The key instrument is the K-band ranging system which continuously measures the changes of the distance between the two GRACE satellites with an accuracy of a few micrometer. Thanks to the success of this mission, proposals have been made for the development of a GRACE-follow-on mission and a next-generation GRACE satellite system, respectively. Apart from options for a multi-satellite mission, the major improvement will be the replacement of the microwave based K-band ranging system by laser interferometry (Bender et al., 2003). The expected improvement in the accuracy is in the range of a factor 10 to 1000.
+
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.
−
Two types of solution strategies exist for the determination of gravity field quantities from kinematic observations (range, range-rate and range-acceleration). The first type is based on numerical integration. The most common ones are the classical integration of the variational equations (Reigber, 1989; Tapley et al., 2004a), the Celestial Mechanics Approach (Beutler et al., 2010) or the short-arc method (Mayer-Gürr, 2006). The second type of solution strategies tries to make use of in-situ (pseudo)-observa-tions. The most typical ones are the energy balance approach (Jekeli, 1998; Han, 2003), the relative accelera-tion approach (Liu, 2008) or the line-of-sight gradiometry approach (Keller and Sharifi, 2005).
+
 
−
From a theoretical point of view all approaches are in one way or the other based on Newton's equation of motion and thus all of them should be applicable to the next generation of satellite missions as well. Practically, problems arise due to the necessity of approximations and linearizations, the accumulation of errors, the combination of highly-precise with less precise quantities, e.g. K-band with GPS, and the incorporation of auxiliary measure-ments, e.g. accelerometer data. These problems are often circumvented by introducing reference orbits, reducing the solution strategies to residual quantities, and by frequently
+
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.  
−
solving for initial conditions and/or additional empirical or stochastic parameter. In the context of the next generation of low-low satellite-to-satellite tracking systems, the question is whether these methods are still sufficient to fully exploit the potential of the improved range observations.
 
  
 
===Objectives===
 
===Objectives===
−
Observations are related to gravity field quantities by means of geometry, kinematics and dynamics. The gravity field is then represented by global or local base functions. The focus of this study group is primarily on the use of spherical harmonics as base function with different approaches to relate the observations to the gravity field. However, since local methods also proofed to yield high-quality solutions, this group will be affiliated with the pro-posed study group on the "Methodology of Regional Gravity Field Modelling" by M. Schmidt and Ch. Gerlach in order to investigate the interplay with regional model-ling. The usage of other global base functions is also wel-come.
 
−
The objectives of the study group are therefore to:
 
−
* investigate each solution strategy, identify approxima-tions and linearizations and test them for their permissibility to the next generation of inter-satellite range obser-vations,
 
−
* identify limitations or the necessity for additional and/or more accurate measurements,
 
−
* quantify the sensitivity to error sources, e.g. in tidal or non-gravitational force modelling,
 
−
* investigate the interaction with global and local modelling,
 
−
* extend the applicability to planetary satellite mission, e.g. GRAIL,
 
−
* establish a platform for the discussion and in-depth understanding of each approach and provide documentation.
 
−
It will not be the objective of this study group to identify the “best” approach as from a theoretical point of view all approaches are able to yield a solution as long as the neces-sary observations with sufficient accuracy have been made and approximations and linearization errors remain below the proposed accuracy of the new range observation. Fur-ther, solutions need validation which is done best with different and independent solution strategies in order to identify possible systematic effects.
 
  
−
===Methodology and Output===
+
The theoretical frameworks of the sub-centimeter geoid/quasi-geoid consist of, but are not limited to, the following components to study:
−
The investigation will be based on an in-depth analysis of the theoretical foundations of each approach in combina-tion with a simulation study with step-wise increasing realism. The preparation of the simulated data set and each approach will be assigned separate work packages with subtasks, which include the above mentioned objectives. Each member is supposed to assign himself to at least one work package and contribute by adding to the discussion of the principles of each approach, supplying simulated data sets, carry out numerical investigations or develop solutions to specific problems.
+
* Physical constant GM
−
The primary output is the result of the collaborative investigation of the different approaches aiming at the identification of possible challenges and the development of solutions ensuring their applicability to the next generation of inter-satellite range observations. These findings are supposed to be well documented in journal paper, possibly in a special issue of Journal of Geodesy or similar by the end of 2014. A workshop is envisaged in the vicinity of the Hotine-Marussi symposium in 2013.
+
* W0 convention and changes
 +
* 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===
  
 +
* The study group achieves its objectives through organizing splinter meetings in coincidence with major IAG conferences and workshops if possible.
 +
* Circulating and sharing progress reports, papers and presentations.
 +
* Presenting and publishing papers in the IAG symposia and scientific journals.
  
 
===Members===
 
===Members===
−
 
+
−
'' '''Matthias Weigelt (Germany), chair<br /> Adrian Jäggi (Switzerland), chair'''<br />
+
'' '''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 />''
−
Markus Antoni (Germany)<br />
 
−
Oliver Baur (Austria)<br />
 
−
Richard Biancale (France)<br />
 
−
Sean Bruinsma (France)<br />
 
−
Christoph Dahle (Germany)<br />
 
−
Christian Gerlach (Germany)<br />
 
−
Thomas Gruber (Germany)<br />
 
−
Shin-Chan Han (USA)<br />
 
−
Hassan Hashemi Farahani (The Netherlands)<br />
 
−
Wolfgang Keller (Germany)<br />
 
−
Jean-Michel Lemoine (France)<br />
 
−
Anno Löcher (Germany)<br />
 
−
Torsten Mayer-Gürr (Austria)<br />
 
−
Philip Moore (UK)<br />
 
−
Himanshu Save (USA)<br />
 
−
Mohammad Sharifi (Iran)<br />
 
−
Natthachet Tangdamrongsub (Taiwan)<br />
 
−
Pieter Visser (The Netherlands)<br />''
 
−
 
 
−
====Corresponding members====
 
−
''Christian Gruber (Germany)<br />
 
−
Majid Naeimi (Germany)<br />
 
−
Jean-Claude Raimondo (Germany)<br />
 
−
Michael Schmidt (Germany)<br />''
 

Latest revision as of 12:27, 24 April 2016

JSG 0.15: Regional geoid/quasi-geoid modelling – Theoretical framework for the sub-centimetre accuracy

Chairs: Jianliang Huang (Canada)
Affiliation: Comm. 2 and GGOS

Problem statement

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.

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.

Objectives

The theoretical frameworks of the sub-centimeter geoid/quasi-geoid consist of, but are not limited to, the following components to study:

  • Physical constant GM
  • W0 convention and changes
  • 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

  • The study group achieves its objectives through organizing splinter meetings in coincidence with major IAG conferences and workshops if possible.
  • Circulating and sharing progress reports, papers and presentations.
  • Presenting and publishing papers in the IAG symposia and scientific journals.

Members

Jianliang Huang (Canada), chair
Yan Ming Wang (USA), vice-chair
Riccardo Barzaghi (Italy)
Heiner Denker (Germany)
Will Featherstone (Australia)
René Forsberg (Denmark)
Christian Gerlach (Germany)
Christian Hirt (Germany)
Urs Marti (Switzerland)
Petr Vaníček (Canada)

Retrieved from "http://icct.kma.zcu.cz/index.php?title=IC_SG6&oldid=226"