Difference between revisions of "JSG T.27"

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===Terms of Reference===
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===Introduction===
  
Observations provided by space geodetic techniques deliver a global picture of the changing system Earth, in particular temporal changes of the Earth’s gravity field, irregularities in the Earth rotation and variations of station positions due to various geodynamical phenomena. Different techniques are characterized by different accuracy and different sensitivity to geodetic parameters, e.g., GNSS provides most accurate pole coordinates, but cannot provide the absolute information on UT1-UTC, and thus, must be integrated with VLBI or LLR data. GRACE observations provide state-of-the-art and most accurate information on temporal changes of the gravity field, but the temporal changes of the Earth’s oblateness or the geocentre motion can be better determined using SLR data. Therefore, a fusion of various space geodetic observations is an indispensable prerequisite for a reliable description of the varying system Earth.
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Consequences of upper-atmosphere conditions on human activity underscore the necessity to better understand and predict effects of the magnetosphere-ionosphere-thermosphere (MIT) processes and of their coupling. This will prevent from their potential detrimental effects on orbiting, aerial and ground-based technologies. For instance, major concerns include the perturbation of electromagnetic signals passing through the ionosphere for an accurate and secure use of global navigation satellite systems (GNSS), and the lack of accurate aerodynamic-drag models required for accurate tracking, decay and re-entry calculations of low Earth orbiters (LEO), including manned and unmanned artificial satellites. In addition, ground power grids and electronics of satellites could be influenced, e.g., by the magnetic field generated by sudden changes in the current system due to solar storms.  
 
However, the space geodetic observations are typically not free of artifacts related to deficiencies in various models used in the data reduction process. GNSS satellite orbits are very sensitive to deficiencies in solar radiation pressure modeling affecting, e.g., the accuracy of GNSS-derived Earth rotation parameters and geocentre coordinates. Deficiencies in modeling of antenna phase center offsets, albedo and the antenna thrust limit the reliability of GNSS and DORIS-derived scale of the terrestrial reference frame, despite a good global coverage of GNSS receivers and DORIS beacons. VLBI solutions are affected by an inhomogeneous quality delivered by different stations and antenna deformations. SLR technique is affected by the Blue-Sky effect which is related to the weather dependency of laser observations and the station-dependent satellite signature effect due to multiple reflections from many retroreflectors. Moreover, un-modeled horizontal gradients of the troposphere delay in SLR analyzes also limit the quality of SLR solutions. Finally, GRACE data are very sensitive to aliasing with diurnal and semidiurnal tides, whereas GOCE and Swarm orbits show a worse quality around the geomagnetic equator due to deficiencies in ionosphere delay modeling.
 
  
Separation of real geophysical signals and artifacts in geodetic observations yield a very challenging objective. A fusion of different observational techniques of space geodesy may enhance our knowledge on systematic effects, improve the consistency between different observational techniques, and may help us to mitigate artifacts in the geodetic time series.
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Monitoring and predicting Earth’s upper atmosphere processes driven by solar activity are highly relevant to science, industry and defence. These communities emphasize the need to increment the research efforts for better understanding of the MIT responses to highly variable solar conditions, as well as detrimental space weather effects on our life and society. On one hand, electron-density variations produce perturbations in speed and direction of various electromagnetic signals propagated through the ionosphere, and reflect as a time-delay in the arrival of the modulated components from which pseudo-range measurements of GNSS are made, and an advance in the phase of signal’s carrier waves which affects also carrier-phase measurements. On the other hand, an aerodynamic drag associated with neutral-density fluctuations resulting from upper atmospheric expansion/contraction in response to variable solar and geomagnetic activity increases drag and decelerates LEOs, dwindling the lifespan of space-assets, and making their tracking difficult.
 
 
The mitigation of artifacts using parameters derived by a fusion of different techniques of space geodesy should comprise three steps: 1) identification of an artifact through an analysis of geodetic parameters derived from multiple techniques; 2) delivering a way to model an artifact; 3) applying the developed model to standard solutions by the analysis centers.
 
 
 
Improving the consistency level through mitigating artifacts in space geodetic observations will bring us closer to fulfilling the objectives of the Global Geodetic Observing System (GGOS), i.e., the 1-mm accuracy of positions and 0.1-mm/year accuracy of the velocity determination. Without a deep knowledge of systematic effects in satellite geodetic data and without a proper modeling thereof, the accomplishment of the GGOS goals will never be possible.  
 
  
 +
Through interrelations, dependencies and coupling patterns between ionosphere, thermosphere and magnetosphere variability, this JSG aims to improve the understanding of coupled processes in the MIT system, and considerations of the solar contribution. In addition, tides from the lower atmosphere forcing can feed into the electrodynamics; they have a composition effect leading to changes in the MIT system. In this scheme, our tasks are addressed to exploit the knowledge of the tight MIT coupling by investigating multiple types of magnetosphere, ionosphere and thermosphere observations. The final outcome will help to enhance the predictive capability of empirical and physics-based models through interrelations, dependencies and coupled patterns of variability between essential geodetic variables.
 +
 
===Objectives===
 
===Objectives===
  
* Developing of data fusion methods based on geodetic data from different sources
+
* Characterize and parameterize global modes of MIT variations associated with diurnal, seasonal and space weather drivers as well as the lower atmosphere forcing.
* Accuracy assessment and simulations of geodetic observations in order to fulfil GGOS’ goals
+
* Determine and parameterize mechanisms responsible for discrepancies between observables and present models.
* Study time series of geodetic parameters (geometry, gravity and rotation) and other derivative parameters (e.g., troposphere and ionosphere delays) determined using different techniques of space geodesy
+
* Detect and investigate coupled processes in the MIT system for the deciphering of physical laws and principles such as continuity, energy and momentum equations and solving partial differential equations.
* Investigating biases and systematic effects in single techniques
 
* Combination of satellite geodetic observations at the observation level and software synchronization
 
* Investigating various methods of technique co-locations: through local ties, global ties, co-location in space
 
* Identifying artifacts in time series of geodetic parameters using e.g., spatial, temporal, and spectral analyzes
 
* Elaborating methods aimed at mitigating systematic effects and artifacts
 
* Determination of the statistical significance levels of the results obtained by techniques using different methods and algorithms
 
* Comparison of different methods in order to point out their advantages and disadvantages
 
* Recommendations for analysis working groups and conventions
 
  
 
===Planned Activities===
 
===Planned Activities===
  
* Preparing a web page with information concerning integration and consistency of satellite geodetic techniques and their integration with special emphasis on exchange of ideas, providing and updating bibliographic list of references of research results and relevant publications from different disciplines.
+
* Presenting research findings at major international geodetic or geophysical conferences, meetings, and workshops.
* Working meetings at the international symposia and presentation of research results at the appropriate sessions.
+
* Interacting with related IAG Commissions and GGOS.
 +
* Monitoring research activities of the JSG members and of other scientists, whose research interests are related to the scopes of SG
 +
* Organizing a session at the Hotine-Marussi Symposium 2022.
 +
* Organizing working meetings at international symposia and presentation of research results at appropriate sessions.
  
 
===Members===
 
===Members===
  
'' '''Krzysztof Sośnica (Poland), chair''' <br /> Toshimichi Otsubo (Japan) <br /> Daniela Thaller (Germany) <br /> Mathis Blossfeld (Germany) <br /> Andrea Maier (Switzerland) <br /> Claudia Flohrer (Germany) <br /> Agnieszka Wnek (Poland) <br /> Sara Bruni (Italy) <br /> Karina Wilgan (Poland) <br />''
+
'' '''Andres Calabia Aibar (China), chair''' <br />
 +
Emmanuel Abiodun Ariyibi (Nigeria) <br />
 +
Toyese Tunde Ayorinde (Brazil) <br />
 +
Olawale S. Bolaji (Nigeria) <br />
 +
Oluwaseyi Emmanuel Jimoh (Nigeria) <br />
 +
Gang Lu (USA) <br />
 +
Naomi Maruyama (USA) <br />
 +
Astrid Maute (USA) <br />
 +
Piyush M. Metha (USA) <br />
 +
Charles Owolabi (Nigeria) <br />
 +
Liang Yuan (China) <br />''

Revision as of 10:45, 10 June 2020

JSG T.27: Coupling processes between magnetosphere, thermosphere and ionosphere

Chair: Andres Calabia Aibar (China)
Affiliation: Commission 4 and GGOS

Introduction

Consequences of upper-atmosphere conditions on human activity underscore the necessity to better understand and predict effects of the magnetosphere-ionosphere-thermosphere (MIT) processes and of their coupling. This will prevent from their potential detrimental effects on orbiting, aerial and ground-based technologies. For instance, major concerns include the perturbation of electromagnetic signals passing through the ionosphere for an accurate and secure use of global navigation satellite systems (GNSS), and the lack of accurate aerodynamic-drag models required for accurate tracking, decay and re-entry calculations of low Earth orbiters (LEO), including manned and unmanned artificial satellites. In addition, ground power grids and electronics of satellites could be influenced, e.g., by the magnetic field generated by sudden changes in the current system due to solar storms.

Monitoring and predicting Earth’s upper atmosphere processes driven by solar activity are highly relevant to science, industry and defence. These communities emphasize the need to increment the research efforts for better understanding of the MIT responses to highly variable solar conditions, as well as detrimental space weather effects on our life and society. On one hand, electron-density variations produce perturbations in speed and direction of various electromagnetic signals propagated through the ionosphere, and reflect as a time-delay in the arrival of the modulated components from which pseudo-range measurements of GNSS are made, and an advance in the phase of signal’s carrier waves which affects also carrier-phase measurements. On the other hand, an aerodynamic drag associated with neutral-density fluctuations resulting from upper atmospheric expansion/contraction in response to variable solar and geomagnetic activity increases drag and decelerates LEOs, dwindling the lifespan of space-assets, and making their tracking difficult.

Through interrelations, dependencies and coupling patterns between ionosphere, thermosphere and magnetosphere variability, this JSG aims to improve the understanding of coupled processes in the MIT system, and considerations of the solar contribution. In addition, tides from the lower atmosphere forcing can feed into the electrodynamics; they have a composition effect leading to changes in the MIT system. In this scheme, our tasks are addressed to exploit the knowledge of the tight MIT coupling by investigating multiple types of magnetosphere, ionosphere and thermosphere observations. The final outcome will help to enhance the predictive capability of empirical and physics-based models through interrelations, dependencies and coupled patterns of variability between essential geodetic variables.

Objectives

  • Characterize and parameterize global modes of MIT variations associated with diurnal, seasonal and space weather drivers as well as the lower atmosphere forcing.
  • Determine and parameterize mechanisms responsible for discrepancies between observables and present models.
  • Detect and investigate coupled processes in the MIT system for the deciphering of physical laws and principles such as continuity, energy and momentum equations and solving partial differential equations.

Planned Activities

  • Presenting research findings at major international geodetic or geophysical conferences, meetings, and workshops.
  • Interacting with related IAG Commissions and GGOS.
  • Monitoring research activities of the JSG members and of other scientists, whose research interests are related to the scopes of SG
  • Organizing a session at the Hotine-Marussi Symposium 2022.
  • Organizing working meetings at international symposia and presentation of research results at appropriate sessions.

Members

Andres Calabia Aibar (China), chair
Emmanuel Abiodun Ariyibi (Nigeria)
Toyese Tunde Ayorinde (Brazil)
Olawale S. Bolaji (Nigeria)
Oluwaseyi Emmanuel Jimoh (Nigeria)
Gang Lu (USA)
Naomi Maruyama (USA)
Astrid Maute (USA)
Piyush M. Metha (USA)
Charles Owolabi (Nigeria)
Liang Yuan (China)