International Association of Geodesy


SC 4.3: Remote Sensing and Modeling of the Atmosphere




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SC 4.2

SC 4.3

SC 4.4


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Terms of Reference

The Earth’s atmosphere can be structured into various layers depending on physical parameters such as temperature or charge state. From the geodetic point of view the atmosphere is nowadays not only seen as a disturbing quantity which has to be corrected but also as a target quantity, since almost all geodetic measurement techniques provide valuable information about the atmospheric state.

Space weather and especially its impacts and risks are gaining more and more importance in politics and sciences, since our modern society is highly depending on space-borne techniques, e.g., for communication, navigation and positioning. Coupling processes between different atmospheric layers and inter-relations with climate change are other contemporary issues.

The general objectives of this SC are to coordinate research on the one hand side in understanding processes within and between the different atmospheric layers using space-geodetic measurements and observations from other branches such as astrophysics and on the other hand in developing new strategies, e.g., for prediction and real-time modelling.

Since GNSS is characterised as a highly precise observation technique it covers a wide range of applications and allows for a huge number of research topics. Besides sounding the atmosphere and studying space weather effects by modern evaluation methods, the promising GNSS reflectometry technique (GNSS-R) is another research topic within this SC.     



Steering Committee

Chair: Michael Schmidt (Germany)

Vice-Chair: Jaroslaw Bosy (Poland)




·       Bridging the gaps between modern geodetic observation techniques such as radio occultations or GNSS reflectometry, measurements from other scientific branches such as astrophysics and geophysics with the geodetic community

·       Improvement of the understanding of space weather with respect to the whole cause and effect chain

·       Investigation of the impact of solar events such as CMEs and solar flares on technical systems and satellite observation techniques

·       Investigation of ionosphere phenomena such currents or scintillations

·       Investigation the coupling processes between different layers within the atmosphere

·       Estimation of thermosphere target parameters and studying their influences on satellite missions

·       Support of atmosphere prediction models based on the combination of  data from different observation techniques, e.g. by developing sophisticated estimation procedures

·       Improvement of precise positioning and navigation on the basis of new atmosphere models

·       Development of real- and near real-time techniques for atmosphere monitoring

·       Study of the influence of the atmosphere on climate change


Program of activities


·       To promote research collaboration among groups from geodesy and other branches worldwide dealing with atmosphere research and applications

·       To organize and/or participate in scientific and professional meetings (workshops, conference sessions, etc.)

·       To maintain a web page concatenating the Sub-Commission activities and reports

·       To encourage special issues, e.g. of Journal of Geodesy, on research, applications, and activities related to the topics of this Sub-Commission



SG 4.3.1 Ionospheric and Atmospheric Coupling Processes and Phenomena: Modeling and Measurements


Chair: Lucie Rolland (France)

Vice-Chair: Attila Komjathy (USA)




This SG aims at better understanding the coupling processes within the Earth’s atmosphere and more generally between the solid Earth and its external envelopes including oceans, neutral atmosphere and the ionosphere using the help of geodetic techniques. Ionospheric disturbances from disruptive phenomena such as – but not limited to – large earthquakes, volcanic eruptions, tsunamis, meteorological or geomagnetic storms are now routinely observed using total electron content (TEC) measurements from GNSS indicating that the Earth’s internal and external processes are closely coupled. More specifically, the SG’s aims are:



·       The development of new detection capabilities (e.g., multi-GNSS, radar imagery, etc.). 

·       The characterization and classification of ionospheric signatures, transients or TIDs (traveling ionospheric disturbances), in terms of amplitude, duration, frequencies, wavelengths, etc., as they relate to the source of the phenomena (natural or hand-made, telluric, atmospheric or ionospheric, etc.).

·       The development of algorithms and methods for quantitative modeling of acoustic-gravity waves and novel designs of inversion strategies of physical parameters defining the source.

·       Further developing data collection techniques along with establishing geodetic databases of coupled phenomena using non-geodetic observations (airglow, infrasounds, etc.).



WG 4.3.1 Real-time Ionosphere Monitoring


Chair: Alberto Garcia-Rigo (Spain)

Vice-Chair: David Roma Dollase (Spain)




Currently, near real-time or even real-time procedures are under development to monitor and analyse the state of the ionosphere and to predict ionosphere target parameters such as the electron density or the vertical total electron content. 

The objectives of this WG are

·        Summary of the current status of RT Ionosphere Monitoring.

·        Comparison of existing RT Ionosphere Monitoring approaches from different perspectives for a specific event, such as the recent St. Patrick's Day 2015 Geomagnetic Storm.

·        Procedure to automatically compare on a daily basis a subset of real time ionosphere products providing the results in a common compatible IONEX format. Potential validation with external data sources, such as JASON2.

·        Open discussion towards new concept(s) on RT Ionosphere Monitoring (through a common mailing list).

·        Dissemination activities (publication on international congresses and in international journals)

This WG aims to work in close scientific collaboration with members from IGS RT-WG, URSI and COSPAR IRI, among others.



WG 4.3.2 Ionosphere Predictions

Chair: Mainul Hoque (Germany)




The general objective of this study group is the development of ionosphere prediction algo­rithm/models based on the dependence of ionospheric characteristics on solar and magnetic conditions as well as on the region of the Earth. Ionospheric disturbances can affect technologies in space and on Earth disrupting satellite and airline operations, communications networks, navigation systems. As the world becomes ever more dependent on these technologies, ionospheric disturbances as part of space weather poses an increasing risk to the economic vitality and national security. Therefore, having the knowledge of the ionospheric state in advance during space weather events is becoming more and more important.

As part of the working group activities we will arrange splinter meetings during international conferences (e.g., EGU, ION GNSS) depending on the availability of members.

Within the next four years we will focus on

·       the development of algorithms for estimating and forecasting ionospheric parameters worldwide based on data from geodetic observation systems, (e.g., GNSS) – the approach may take advantage of the ionospheric movement from east to west,

·       performing first steps by introducing physics-motivated functions into the iono­spheric parameters estimation process with respect to the inclusion of Sun and magnetic observations,

·       combining data from differ­ent sensors to improve the spatial and temporal resolution and sensitivity taking advantage of different sounding geometries and latency.



JWG 4.3.3 Combination of Observation Techniques for Multi-dimensional Ionosphere Modelling

(joint with GGOS)


Chair: Mahdi M. Alizadeh (Germany)




The general objective of this working group is the development of regional and global ionosphere maps of VTEC and electron density in 2D, 3D, and 4D; based on the combination of various observation techniques. Several observation techniques including space geodetic techniques allow monitoring and modelling of the ionosphere parameters, such as the electron density or the vertical total electron content (VTEC), but each technique has its specific characteristics which influence the derived parameters. Combining measurements from different techniques will provide more homogeneous maps with higher reliability and improved accuracy.

This JWG will contribute extensively to the aims of GGOS, which is integrating different geodetic techniques, different models, and different approaches in order to ensure a long-term, precise monitoring of the geodetic observables in agreement with the Integrated Global Observing Strategy (IGOS).

Objectives within the next four years we will:


Thus, this JWG will provide integrated global and regional maps of VTEC and peak ionosphere parameters from the combination of various space geodetic techniques. These products are interpretable as GGOS products following the strategy defined at the GGOS days 2015 in Frankfurt. 



WG 4.3.4 Ionosphere and Troposphere Impact on GNSS Positioning


Chair: Tomasz Hadas (Poland)



Atmosphere effects are still one of the major factors limiting GNSS precise positioning. One possibility to overcome this limitation is to augment the positioning with precise external model. The ionosphere information is particularly important for processing long baselines, single frequency data and ambiguity resolution. The troposphere model can improve the convergence time and height estimation, particularly in real-time kinematic positioning. Further research is needed in detailed analysis of the atmosphere impact on GNSS positioning.

For this purpose the WG will



WG 4.3.5 Ionosphere Scintillations


Chair: Lung-Chih Tsai (Taiwan) 

Vice-Chair: Jens Berdermann (Germany)




Ionospheric scintillation has significant impacts on satellite radio communication and navigation system performance. The main effects of scintillation on transionospheric radio system are signal loss and phase cycle slips, causing difficulties in the signal lock of receivers. There is no doubt that scintillation of satellite radio signals is a consequence of the existence of random electron density fluctuations within the ionosphere. There could be different sources for ionospheric instabilities/irregularities at different areas and geophysical conditions.


The objectives of this WG are



WG 4.3.6 Troposphere Tomography

Chair: Witold Rohm (Poland)



GNSS troposphere tomography technique is gradually gaining interest around the world as new researchers start investigate this concept, with new implementations being announced quite frequently. In the coming years we will see dramatic increase of number of available observations from dense GNSS networks and new satellite constellations such as Galileo, Baidou, QZSS or IRSS. As the slant troposphere delay estimation strategies are being intensively reinvestigated, the number and quality of standard tomography observations will be tripled or quadrupled.

This poses an opportunity for tomography application in the field of meteorology for monitoring, nowcasting and forecasting. The tomography models could be applied to independently resolve vertical and horizontal structure of weather phenomenon, if this could be done with high temporal resolution it would be an important input for nowcasting systems. On the other hand a number of STDs might overload the assimilation systems and the assimilation algorithms might not be optimal for exploiting the information provided by slants. An intermediate tomography step might solve these problems. However, successful implementation of tomography models in the weather services is hampered by several factors, such as (1) the unknown retrieval accuracy, (2) an unstable solution that may vary from epoch to epoch, and (3) a low vertical and horizontal resolution.

The objectives of this WG are

·       Quality assurance factors in GNSS tomography processing, investigating new mapping techniques, operator monitoring schemes and use (in the early stage) synthetic observations, [QUALITY]

·       Optimal combination of GNSS observations with other troposphere measurements in GNSS tomography models, [COMBINATION]

·       Use of tomography retrievals in severe weather investigation, [SEVERE]

·       Use of tomography retrieval in weather system assimilation. [ASSIMILATION]



WG 4.3.7 Real-time Troposphere Monitoring

Chair: Jan Dousa (Czech Republic)




The main objective of this WG is to develop, optimize and assess new real-time or ultra-fast tropospheric products using data from GNSS permanent networks. Tropospheric zenith total delays, tropospheric linear horizontal gradients, slant delays, integrated water vapour (IWV) maps or other derived products in sub-hourly fashion are foreseen for future exploitation in numerical and non-numerical weather nowcasting or severe weather event monitoring.

The use of Precise Point Positioning (PPP) processing strategy will play a key role in developing new products because it is an efficient and autonomous method, it is sensitive to absolute tropospheric path delays, it can effectively support real-time or ultra-fast production, it may optimally exploit data from all GNSS multi-constellations, it can easily produce a full variety of parameters such as zenith total delays, horizontal gradients or slant path delays and it may also support as reasonable as high temporal resolution of all the parameters. Last, but not least, the PPP is supported with the global orbit and clock products provided by the real-time service of the International GNSS Service (IGS).

The objectives of this WG are

·       Develop optimal strategies for real-time/ultra-fast tropospheric products suitable for numerical or non-numerical weather nowcasting applications or severe weather event monitoring.

·       Stimulate development of application software for supporting routine production.

·       Demonstrate real-time/ultra-fast production, assess applied methods, software and precise orbit and clock products.

·       Evaluate tropospheric parameters and their potential for applications in meteorology

·       Setup a link to the potential users, review product format and requirements.



JWG 4.3.8: GNSS tropospheric products for Climate

(joint with Commission 1)


Chair: Rosa Pacione (Italy)

Vice-Chair:  Eric Pottiaux (Belgium)




In many part of the world, huge efforts are ongoing for providing homogeneously reprocessed GNSS solutions that are the basis for deriving very precise coordinates, velocities and troposphere parameters (namely Zenith Total tropospheric Delays and Horizontal Gradients). These regional and global reprocessing campaigns are possible thanks to the availability of 19+ years of observations from permanently observing GNSS stations located worldwide (e.g. the IGS network), their regional densifications (e.g. the EPN network), and of reprocessed global orbit and clock products (e.g. those provided by the IGS Analysis Centers). These long-term time series of homogeneously reprocessed troposphere parameters will provide a GNSS climate data record with high potential for climate monitoring. Unfortunately, these time series still suffer from inhomogeneities (for example instrumental changes, changes in the station environment) which can affect the analysis of the long-term variability.

The main objective of the working group is to assess existing reprocessed GNSS tropospheric products, foster the development of forthcoming reprocessing activities and promote their use for climate research.

The objectives of this WG are:

·       Assess existing reprocessed troposphere solutions and provide recommendations for the forthcoming reprocessing activities.

·       Set-up a common GNSS climate dataset on which different homogenization methodologies can be tested. The homogenized common long-term dataset can then be reused for climate trends and variability studies within the community.

·       Stimulate the data assimilation of GNSS troposphere products in Climate Models.

·       Review and update GNSS-based product requirements and exchange format for climate.

·       Strengthen the cooperation between geodesists and climatologists.



JWG 4.3.9 GNSS-R

(joint with GGOS)


Chair: Felipe Nievinski (Brazil)

Vice-Chair: Thomas Hobiger (Sweden)




Global Navigation Satellite Systems (GNSS) have not only revolutionized positioning, navigation, and timing but also lead to the development of many other applications which were not anticipated when those satellite systems were designed decades ago. The most prominent example for a novel application from recent years is the usage of reflected GNSS signals as a new tool for remote sensing. GNSS Reflectometry (GNSS-R) enables us to derive geometric and physical characteristics of the reflecting surface by analysing and interpreting features of the received signals. GNSS-R has started to make an impact in the discipline of remote sensing but it still has not reached the focus of a broader geodetic community although topics like sea-level monitoring, hydrological loading, and water cycle and drought/flooding observations are highly relevant to the goals of the Global Geodetic Observing System (GGOS). Thus, the overall aim of this working group is to bridge the gap between GNSS-R and the geodetic community, by seeking to raise the awareness of its relevance to several geodetic problems as well as opportunities.


The objectives of this WG are

·       Identify GNSS-R products which have a strong relation to IAG services and goals.

·       Foster and establish interactions with neighbouring societies (such as the IEEE Geoscience and Remote Sensing Society, GARSS) and cooperate with technological, engineering, and operational entities related to GNSS (e.g., the International GNSS Service, IGS), identifying common goals and detecting potential synergies.

·       Provide an online inventory of GNSS-R products relevant to geodesy and point to corresponding data archives.

·       Evaluate the possibility to obtain formal errors for GNSS-R products in order to enable better combination with other datasets.

·       Provide guidelines and define formats for GNSS-R products being used for geodetic purposes.

·       Organize working meetings with GNSS-R experts, while also inviting stakeholders from the geodetic community to participate in such events.

·       Extend IGS Site Guidelines so as to maximize the shared usefulness of new GNSS site installations for reflectometry applications.

·       Supplement the GNSS-R Campaign Spreadsheet (initiated by the IEEE GRSS) so as to list existing GNSS tracking stations that can be leveraged for reflectometry purposes.

·       Evaluate the feasibility of a pilot project on GNSS-R for coastal sea level monitoring, demonstrating its current level of maturity towards an operational service; possibly in cooperation with the IGS Tide Gauge WG (IGS-TIGA).

·       Plan future inter-comparison campaigns for the validation of theoretical model simulations as well as parameter retrievals based on measured data.