Difference between revisions of "JSG T.38"

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<big>'''JSG 0.10: High-rate GNSS'''</big>
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<big>'''JSG T.38: Exploring the similarities and dissimilarities among different geoid/quasigeoid modelling techniques in view of cm-precise and cm-accurate geoid/quasigeoid'''</big>
  
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Chair: ''Mattia Crespi (Italy)''<br>
+
Chair: ''Ropesh Goyal (India)''<br>
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Affiliation:''Commissions 1, 3 4 and GGOS''
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Vice-Chair: ''Sten Classens (Australia)''<br>
 +
Affiliations: ''Commission 2, IGFS''
  
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__TOC__
+
===Terms of Reference===
  
−
===Introduction===
+
It is over 170 years since George Gabriel Stokes published his seminal formula for
 +
geoid determination using gravity anomalies. The formula was derived in spherical
 +
approximation and is valid under some well-known assumptions. Since then, geoid
 +
modelling has revolved more or less around handling these assumptions. As a result,
 +
there are now various geoid and quasigeoid computation methods of both types, i.e.,
 +
methods with and without requiring the Stokes integration. However, despite this
 +
long-elapsed time, the determination of a cm-precise and/or cm-accurate geoid and
 +
quasigeoid remains an ongoing quest, although it has been achieved in a few studies. <br />
  
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Global Navigation Satellite Systems (GNSS) have become for a long time an indispensable tool to get accurate and reliable information about positioning and timing; in addition, GNSS are able to provide information related to physical properties of media passed through by GNSS signals. Therefore, GNSS play a central role both in geodesy and geomatics and in several branches of geophysics, representing a cornerstone for the observation and monitoring of our planet.
+
With the computation of cm-precise and/or cm-accurate geoid, a supposition can
 +
be formed that solutions from different geoid modelling methods should converge
 +
within a given threshold, with an ideal threshold value being one-cm. The rationale is
 +
that, for a region, all the methods can be used to calculate the geoid using the same
 +
data and underlying theory. Still, methods differ primarily due to different handling
 +
of the data, and assumptions and approximations. Different methods provide different
 +
solutions due to many aspects including but not limited to: 1. different modifications
 +
of Stokes’s kernel, 2. different prediction/interpolation/extrapolation methods for
 +
non-Stokes integrating geoid modelling methods, 3. use of geodetic versus geocentric
 +
coordinates, 4. different Global Geopotential Models, 5. different gridding and merging
 +
techniques, 6. different parameter sweeps (integration radius and kernel modification
 +
degree), and 7. different handling of topography, atmosphere, spherical approximation,
 +
and downward continuation. <br />
  
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So, it is not surprising that, from the very beginning of the GNSS era, the goal was pursued to widen as much as possible the range in space (from local to global) and time (from short to long term) of the observed phenomena, in order to cover the largest possible field of applications, both in science and in engineering; two complementary, but primary as well, goals were, obviously, to get these information with the highest accuracy and in the shortest time.  
+
Given these possible sources for differences in geoid models, it becomes inevitable
 +
to first create a rigorous definition of a “cm-precise” and “cm-accurate” geoid followed
 +
by a comparative study of intermediate steps of different geoid modelling methods,
 +
in addition to comparing only the final results from different methods separately.
 +
Comparative study of intermediate steps is essential given the fact that if using the
 +
same datasets in different methods, it is expected to have geoid differences less than
 +
one cm when the methods are designed to take into account all effects greater than
 +
one cm. <br />
  
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The advances in technology and the deployment of new constellations, after GPS (in the next years will be completed the European Galileo, the Chinese Beidou and the Japanese QZSS) remarkably contributed to transform this three-goals dream in reality, but still remain significant challenges when very fast phenomena have to be observed, mainly if real-time results are looked for.
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Further, in view of cm-precise and/or cm-accurate geoid, it is important to compare
−
 
+
multiple methods and parameter sweeps in different areas. This is because it would
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Actually, for almost 15 years, starting from the noble birth in seismology, and the very first experiences in structural monitoring, high-rate GNSS has demonstrated its usefulness and power in providing precise positioning information in fast time-varying environments. At the beginning, high-rate observations were mostly limited at 1 Hz, but the technology development provided GNSS equipment (in some cases even at low-cost) able to collect measurements at much higher rates, up to 100 Hz, therefore opening new possibilities, and meanwhile new challenges and problems.
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form an ideal strategy for a consistently precise/accurate geoid model. The difference
−
 
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between the precise geoid and consistently precise geoid is that the precision, in the
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So, it is necessary to think about how to optimally process this potential huge heap of data, in order to supply information of high value for a large (and likely increasing) variety of applications, some of them listed hereafter without the claim to be exhaustive: better understanding of the geophysical/geodynamical processes mechanics; monitoring of ground shaking and displacement during earthquakes, also for contribution to tsunami early warning; tracking the fast variations of the ionosphere; real-time controlling landslides and the safety of structures; providing detailed trajectories and kinematic parameters (not only position, but also velocity and acceleration) of high dynamic platforms such as airborne sensors, high-speed terrestrial vehicles and even athlete and sport vehicles monitoring.
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latter, should be preserved when a geoid model is validated region-wise in addition to
−
 
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the validation with the complete ground truth. Otherwise, cm-precise geoid may have
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Further, due to the contemporary technological development of other sensors (hereafter referred as ancillary sensors) related to positioning and kinematics able to collect data at high-rate (among which MEMS accelerometers and gyros play a central role, also for their low-cost), the feasibility of a unique device for high-rate observations embedding GNSS receiver and MEMS sensors is real, and it opens, again, new opportunities and problems, first of all related to sensors integration.
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limited meaning.
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All in all, it is clear that high-rate GNSS (and ancillary sensors) observations represent a great resource for future investigations in Earth sciences and applications in engineering, meanwhile stimulating a due attention from the methodological point of view in order to exploit their full potential and extract the best information. This is the why it is worth to open a focus on high-rate (and, if possible, real-time) GNSS within ICCT.
 
  
 
===Objectives===
 
===Objectives===
  
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* To realize the inventories of:
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• Develop a statistical definition of cm-precise and cm-accurate geoid/quasi-geoid. <br />
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** the available and applied methodologies for high-rate GNSS, in order to highlight their pros and cons and the open problems,
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• Study and quantify the differences in handling the topography, atmosphere,
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** the present and wished applications of high-rate GNSS for science and engineering, with a special concern to the estimated quantities (geodetic, kinematic, physical), in order to focus on related problems (still open and possibly new) and draw future challenges
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ellipsoidal correction, and downward continuation in different geoid/quasigeoid
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** the technology (hw, both for GNSS and ancillary sensors, and sw, possibly FOSS), pointing out what is ready and what is coming, with a special concern for the supplied observations and for their functional and stochastic modeling with the by-product of establishing a standardized terminology
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modelling methods. <br />
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* To address known (mostly cross-linked) problems related to high-rate GNSS as (not an exhaustive list): revision and refinement of functional and stochastic models; evaluation and impact of observations time-correlation; impact of multipath and constellation change; outliers detection and removal; issues about GNSS constellations interoperability; ancillary sensors evaluation, cross-calibration and  integration
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• Study, quantify and reduce the assumptions and approximations in different geoid
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* To address the new problems and future challanges arised from the inventories
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modelling methods to attain congruency within some threshold. <br />
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* To investigate about the interaction with present real-time global (IGS-RTS, EUREF-IP, etc.) and regional/local positioning services: how can these services support high-rate GNSS observations and, on reverse, how can they benefit of high-rate GNSS observations
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• Study the requirement for merging various components/steps of different geoid
 +
modelling methods. <br />
 +
• Develop external validation techniques to determine region- or nationwide
  
 
===Program of activities===
 
===Program of activities===
  
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* To launch a questionnaire for the above mentioned inventory of methodologies, applications and technologies.
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• Presenting research findings at major international geodetic conferences, meetings,
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* To open a web page with information concerning high-rate GNSS and its wide applications in science and engineering, with special emphasis on exchange of ideas, provision and updating bibliographic list of references of research results and relevant publications from different disciplines.
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and workshops. <br />
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* To launch the proposal for two (one science and the other engineering oriented) state-of-the-art review papers in high-rate GNSS co-authored by the JSG Members.
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• Preparation of joint publications with JSG members. <br />
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* To organize a session at the forthcoming Hotine-Marussi symposium.
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• Organizing a session at the Hotine-Marussi Symposium 2026. <br />
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* To promote sessions and presentation of the  research results at international symposia both related to Earth science (IAG/IUGG, EGU, AGU, EUREF, IGS) and engineering (workshops and congresses in structural and geotechnical engineering).
+
• Organizing splinter meetings at major international conferences and a series of online
 +
workshop. <br />
 +
• Supporting and cooperating with IAG commissions, services, and other study and
 +
working groups on gravity modelling and height systems.
  
 
===Members===
 
===Members===
  
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'' '''Mattia Crespi (Italy), chair''' <br /> Juan Carlos Baez (Chile) <br /> Elisa Benedetti (United Kingdom) <br /> Geo Boffi (Switzerland) <br /> Gabriele Colosimo (Switzerland) <br /> Athanasios Dermanis (Greece) <br /> Roberto Devoti (Italy) <br /> Jeff Freymueller (USA) <br /> Joao Francisco Galera Monico (Brazil) <br /> Jianghui Geng (Germany) <br /> Kosuke Heki (Japan) <br /> Melvin Hoyer (Venezuela) <br /> Nanthi Nadarajah (Australia) <br /> Yusaku Ohta (Japan) <br /> Ruey-Juin Rau (Taiwan) <br /> Eugenio Realini (Italy) <br /> Chris Rizos (Australia) <br /> Nico Sneeuw (Germany) <br /> Peiliang Xu (Japan) <br />''
+
Ropesh Goyal (India); Chair <br />
−
 
+
Sten Claessens (Australia); Vice-Chair <br />  
 +
Ismael Foroughi (Canada) <br />  
 +
Jonas Ågren (Sweden) <br />  
 +
Xiaopeng Li (USA) <br />  
 +
Bihter Erol (Turkey) <br />  
 +
Jack McCubbine (Australia) <br />  
 +
Pavel Novák (Czech Republic) <br />  
 +
Koji Matsuo (Japan) <br />  
 +
Riccardo Barzaghi (Italy) <br />  
 +
Michal Šprlák (Czech Republic) <br />  
 +
Jianliang Huang (Canada) <br />  
 +
Yan-Ming Wang (USA) <br />  
 +
Cheinway Hwang (China-Taipei) <br />  
 +
Neda Darbeheshti (Australia) <br />
  
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===Bibliography===
+
===Associate Members===
  
−
http://icct.kma.zcu.cz/index.php/Special:MovePage/JSG_0.10:_High-rate_GNSS_-_Bibliography
+
Jack McCubbine (Australia) <br />

Latest revision as of 01:30, 1 September 2024

JSG T.38: Exploring the similarities and dissimilarities among different geoid/quasigeoid modelling techniques in view of cm-precise and cm-accurate geoid/quasigeoid

Chair: Ropesh Goyal (India)
Vice-Chair: Sten Classens (Australia)
Affiliations: Commission 2, IGFS

Terms of Reference

It is over 170 years since George Gabriel Stokes published his seminal formula for geoid determination using gravity anomalies. The formula was derived in spherical approximation and is valid under some well-known assumptions. Since then, geoid modelling has revolved more or less around handling these assumptions. As a result, there are now various geoid and quasigeoid computation methods of both types, i.e., methods with and without requiring the Stokes integration. However, despite this long-elapsed time, the determination of a cm-precise and/or cm-accurate geoid and quasigeoid remains an ongoing quest, although it has been achieved in a few studies.

With the computation of cm-precise and/or cm-accurate geoid, a supposition can be formed that solutions from different geoid modelling methods should converge within a given threshold, with an ideal threshold value being one-cm. The rationale is that, for a region, all the methods can be used to calculate the geoid using the same data and underlying theory. Still, methods differ primarily due to different handling of the data, and assumptions and approximations. Different methods provide different solutions due to many aspects including but not limited to: 1. different modifications of Stokes’s kernel, 2. different prediction/interpolation/extrapolation methods for non-Stokes integrating geoid modelling methods, 3. use of geodetic versus geocentric coordinates, 4. different Global Geopotential Models, 5. different gridding and merging techniques, 6. different parameter sweeps (integration radius and kernel modification degree), and 7. different handling of topography, atmosphere, spherical approximation, and downward continuation.

Given these possible sources for differences in geoid models, it becomes inevitable to first create a rigorous definition of a “cm-precise” and “cm-accurate” geoid followed by a comparative study of intermediate steps of different geoid modelling methods, in addition to comparing only the final results from different methods separately. Comparative study of intermediate steps is essential given the fact that if using the same datasets in different methods, it is expected to have geoid differences less than one cm when the methods are designed to take into account all effects greater than one cm.

Further, in view of cm-precise and/or cm-accurate geoid, it is important to compare multiple methods and parameter sweeps in different areas. This is because it would form an ideal strategy for a consistently precise/accurate geoid model. The difference between the precise geoid and consistently precise geoid is that the precision, in the latter, should be preserved when a geoid model is validated region-wise in addition to the validation with the complete ground truth. Otherwise, cm-precise geoid may have limited meaning.

Objectives

• Develop a statistical definition of cm-precise and cm-accurate geoid/quasi-geoid.
• Study and quantify the differences in handling the topography, atmosphere, ellipsoidal correction, and downward continuation in different geoid/quasigeoid modelling methods.
• Study, quantify and reduce the assumptions and approximations in different geoid modelling methods to attain congruency within some threshold.
• Study the requirement for merging various components/steps of different geoid modelling methods.
• Develop external validation techniques to determine region- or nationwide

Program of activities

• Presenting research findings at major international geodetic conferences, meetings, and workshops.
• Preparation of joint publications with JSG members.
• Organizing a session at the Hotine-Marussi Symposium 2026.
• Organizing splinter meetings at major international conferences and a series of online workshop.
• Supporting and cooperating with IAG commissions, services, and other study and working groups on gravity modelling and height systems.

Members

Ropesh Goyal (India); Chair
Sten Claessens (Australia); Vice-Chair
Ismael Foroughi (Canada)
Jonas Ågren (Sweden)
Xiaopeng Li (USA)
Bihter Erol (Turkey)
Jack McCubbine (Australia)
Pavel Novák (Czech Republic)
Koji Matsuo (Japan)
Riccardo Barzaghi (Italy)
Michal Šprlák (Czech Republic)
Jianliang Huang (Canada)
Yan-Ming Wang (USA)
Cheinway Hwang (China-Taipei)
Neda Darbeheshti (Australia)

Associate Members

Jack McCubbine (Australia)

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