SC 2.4: Regional Geoid Determination

Chair: Hussein Abd-Elmotaal
Vice-Chair: Xiaopeng Li (USA)

Terms of Reference and Objectives

Sub-commission 2.4 is concerned with the following areas of investigation:

• Regional gravity and geoid sub-commissions: data sets, involved institutions, comparison of methods and results, data exchange, comparison with global models, connection of regional models
• Gravimetric geoid modelling techniques and methods, available software, new alternative geoid determination techniques
• GPS/levelling geoid determination: methods, comparisons, treating and interpretation of residuals, common treatment of gravity and GPS/levelling for geoid determination
• Geoid applications: GPS heights, sea surface topography, integration of geoid models in GPS receivers, vertical datums.
• Other topics: topographic effects, downward and upward continuation of terrestrial, airborne, satellite data specifically as applied to geoid modelling.

Program of Activities 

Sub-Commission 2.4 is going to initiate and coordinate regional gravity and geoid sub-commissions. It will encourage and support the data exchange between agencies and will assist local, regional and national authorities in their projects of gravity field determination. It will help in organizing courses and symposia for gravity field determination.

Steering Committee 

• Chair SC2.4: Hussein Abd-Elmotaal
• Chair SC2.4a: Heiner Denker (Germany)
• Chair SC2.4b: Maria Cristina Pacino (Argentina)
• Chair SC2.4c: Xiaopeng Li (U.S.)
• Chair SC2.4d: Hussein Abd-Elmotaal (Egypt)
• Chair SC2.4e: Cheinway Hwang (China-Taipei)
• Chair SC2.4f: Mirko Scheinert (Germany)

SC 2.4a: Gravity and Geoid in Europe

Chair: Heiner Denker (Germany)

Terms of Reference

The primary objective of the sub-commission is the development of improved regional geoid and quasigeoid models for Europe, which can be used for applications in geodesy, oceanography, geophysics and engineering, e.g., height determination with GNSS techniques, vertical datum definition and unification, dynamic ocean topography estimation, geophysical modelling, and navigation. Another emerging field is related to the development of new optical clocks in physics with relative uncertainties at the level of 10-18, as in accordance with the laws of general relativity, such clocks are sensitive to the gravity potential at the level of 0.1 m2/s2, equivalent to 1 cm in height.

The geoid and quasigeoid modelling will be based mainly on terrestrial gravity and terrain data in combination with state-of-the-art global geopotential models. In this context, upgraded terrestrial data sets as well as the utilization of GRACE and GOCE based global geopotential models led to significant improvements. The evaluation of the latest European gravimetric quasigeoid models by GNSS and levelling data indicates an accuracy potential of 1 – 2 cm on a national basis, and 2 – 4 cm at continental scales, provided that high quality and resolution input data are available within the area of interest. Further improvements can be expected from the inclusion of upgraded gravity field data sets, especially in areas with hitherto insufficient input data.

Program of Activities 

• Utilization of state-of-the-art global geopotential models.
• Identification and acquisition of new terrestrial data sets, including gravity, terrain, and GPS/levelling data.
• Merging and validation of all data sets.
• Investigation of refined mathematical modelling techniques and numerical tests.
• Computation of new geoid and quasigeoid models.
• Evaluation of the results by GNSS/levelling data.
• Study of applications, such as vertical datum definition and unification, dynamic ocean topography estimation, ground truth for optical clocks, etc.

Delegates

The regional sub-commission for Europe SC2.4a cooperates with national representatives from most of the countries in Europe and reports to sub-commission 2.4. The existing contacts and successful cooperation with the respective persons and national and international agencies shall be continued and extended.

SC 2.4b: Gravity and Geoid in South America

Chair: Maria Cristina Pacino (Argentina)
Vice-Chair: Denizar Blitzko (Brazil)

Terms of Reference and Objectives

The Sub Commission 2.4b entitled Gravity and Geoid in South America, as part of the Commission 2 of IAG, was established as an attempt to coordinate efforts to establish a new Absolute Gravity Network in South America, to carry out gravity densification surveys, to derive a geoid model for the continent as a height reference and to support local organizations in the computation of detailed geoid models in different countries.

Besides, a strong effort is being carried out in several countries in order to improve the distribution of gravity information, to organize the gravity measurements in the continent and to validate the available gravity measurements.

The main objectives of the project are:

• To re-measure existent absolute gravity stations and to encourage the establishment of new stations.
• To validate fundamental gravity network from different countries in order to establish a single and common gravity network for South America.
• To adjust national gravity networks and to link them together.
• To obtain and to maintain files with data necessary for the geoid computation like gravity anomalies, digital terrain models, geopotential models and satellite observations (GPS) on the levelling network of different countries.
• To provide a link between the different countries and the IGFS in order to assure access to proper software and geopotential models for local geoid computation.
• To compute a global geoid model for South and Central America using the available data. To encourage countries to cooperate by releasing data for this purpose.
• To encourage and eventually support local organizations in different countries endeavoring to increase the gravity data coverage, to improve the existing digital terrain models, to carry out GPS observations on the levelling network and to compute a high resolution geoid.
• To organize and/or encourage the organization of workshops, symposia or seminars on gravity and geoid determination in South America.
• To test and to use future geopotential models derived from the modern missions (GRACE and GOCE) as well as any new combined model (e.g. EGM2008).
• To support the IAG Sub-Commission 1.3b (Reference Frame for South and Central America, SIRGAS) in the activities related to the unification of the existing vertical datums.
• Establish close connections with SC2.4c (Gravity and Geoid in North and Central America) to have a good overlap of data coverage in Central America and the Caribbean.

Delegates

• Chair: Maria Cristina Pacino (Argentina)
• Co-Chair: Denizar Blitzkow (Brazil)
• Henry Montecino Castro (Chile)
• Oscar Carranco (Ecuador)
• Ana Crisitina Oliveira Concoro de Matos (Brasil)
• Ayelén Pereira (Argentina)
• Roberto Teixeira Luz (Brasil)
• Silvia Alicia Miranda (Argentina)
• Ivonne Gatica Placencia (Chile)
• Norbertino Suárez (Uruguay)
• Jorge Faure Valbi (Uruguay)

SC 2.4c: Gravity and Geoid in North and Central America

Chair: Xiaopeng Li (USA)
Vice-Chair: David Avalos (Mexico)

Terms of Reference and Objectives

The primary objective of this Sub-commission is the development of a regional gravity field and geoid model covering the region of North America and Central America by 2022 in order to achieve a common vertical datum. The region involved will encompass Iceland, Greenland, Canada, the U.S.A. (including Alaska and Hawaii), Mexico, countries forming Central America, the Caribbean Sea and the northern parts of South America. This model will serve as the official realization of the vertical datum for countries that want to adopt it.

The intention is to ensure that a suitable North American Geoid is developed to serve as a common datum for every- one in the region. All countries in the region would be served by having access to a common model for translating oceanographic effects to terrestrial datums for various scientific, commercial, engineering and disaster prepared-ness applications. Likewise, it shall serve as the basis for the forthcoming International Great Lakes Datumin 2022 (IGLD 2020).

The achievement of a geoid model for North and Central America will be accomplished by coordinating activities among agencies and universities with interest in geoid theory, gravity, gravity collection, gravity field change, geophysical modelling, digital elevation models (DEM), digital density models (DDM), altimetry, dynamic ocean topography, levelling and vertical datums. Of particular interest will be relating geoid and ocean topography models to ocean topography and tidal benchmarks, taking advantage of the recent satellite altimetry and geopotential field products.

The determination of a geoid model for North and Central America is not limited to a single agency, which will collect all necessary data from all countries. The Sub-commission encourages theoretical diversity in the determination of a geoid model among the agencies. Each agency takes responsibility or works in collaboration with neighboring countries in the development of a geoid model for their respective country with an overlap (as large as possible) over adjacent countries. Each solution will be compared, the discrepancies will be analyzed, and the conclusions will be used to improve on the next model.

Program of Activities 

The Sub-commission will support geoid activities in countries where geoid expertise is limited by encouraging more advanced members to contribute their own expertise and software. The Sub-commission will encourage training and education initiative of its delegates (e.g., IGeS geoid school, graduate studies and IPGH technical cooperation projects). Starting on 2011 the Sub-commission will organize regular meetings with representatives of Central American and Caribbean countries to promote an increase of expertise as well as to create a wide network of specialists.

The chair (or a delegate representative) of the Sub-commission will meet with the equivalent European and South American projects to discuss overlap regions and to work towards agreements to exchange data. The delegates of the Sub-commission will keep close contact with all related Study Groups of the IAG. The Sub-commission is open to all geodetic agencies and universities across North and Central America with an interest in the development of a geoid model for the region. The meetings of the Sub-commission 2.4c are open to everyone with interests in geodesy, geo- physics, oceanography and other related topics.

The delegates will communicate primarily using e-mail. In addition, starting on November 9, 2015, Canada (CGS), USA (NGS) and Mexico (INEGI) will organize audio/video conferences every four weeks to discuss activity plans and present results. The sub-commission also plans to organize annual meetings if enough delegates can be present. Preferably, these meetings will be held during international conferences;. Minutes of meetings will be prepared and sent to all delegates of the Sub-commission.

Delegates

• Chair: Xiaopeng Li (USA)
• Vice-Chair: David Avalos (Mexico)
• Rene Forsberg (Denmark)
• Jianliang Huang (Canada)
• Dan Roman (USA)
• Laramie Potts (USA)
• Yan Min Wang (USA)
• Vinicio Robles (Guatemala)
• Carlos E. Figueroa (El Salvador)
• Anthony Watts (Cayman Islands)
• Oscar Meza (Honduras)
• Alvaro Alvarez (Costa Rica)
• Wilmer Medrano (Nicaragua)
• Christopher Ballesteros (Panama)

SC 2.4d: Gravity and Geoid in Africa

Chair: Hussein Abd-Elmotaal (Egypt)
Vice-Chair: S.A. Benahmed Daho (Algeria)

Terms of Reference

The African Gravity and Geoid sub-commission (AGG) belongs to the Commission 2 of the International Association of Geodesy (IAG). The main goal of the African Gravity and Geoid sub-commission is to determine the most complete and precise geoid model for Africa that can be obtained from the available data sets. Secondary goals are to foster cooperation between African geodesists and to provide high-level training in geoid computation to African geodesists.

Objectives and Activities

The objectives and activities of the sub-commission are summarized as follows:

• Identifying and acquiring data sets - gravity anomalies, DTMs, GPS/levelling, seismic Moho.
• Training of African geodesists in geoid computation.
• Merging and validating gravity data sets.
• Computing African geoid models.
• Evaluating the computed geoid models using GPS/levelling data.
• Updating the geoid models using new data/strategies to obtain better geoid accuracy (dynamic process).

Delegates

• Chair: Hussein Abd-Elmotaal (Egypt)
• Vice-Chair: S.A. Benahmed Daho (Algeria)
• Addisu Hunegnaw (Ethiopia) 
• Ahmed Abdalla (Sudan) 
• Atef Makhloof (Egypt)
• Ayman Hassan (Egypt)
• Bernhard Heck (Germany)
• Charles Merry (South Africa) 
• Hassan Fashir (Sudan) 
• Ismail Ateya Lukandu (Kenya) 
• John B.K. Kiema (Kenya) 
• Joseph Awange (Kenya) 
• Joseph Kamguia (Cameroun)
• Karim Owolabi (Namibia)
• Kurt Seitz (Germany)
• Mostafa Abd-Elbaky (Egypt)
• Mostafa Ashry (Egypt)
• Norbert Kühtreiber (Austria)
• Patroba Odera (Kenya)
• Peter Nsombo (Zambia) 
• Prosper Ulotu (Tanzania) 
• Walyeldeen Godah (Sudan)

SC 2.4e: Gravity and Geoid in the Asia-Pacific

Chair: Cheinway Hwang (China-Taipei)
Vice-Chair: Wenbin Shen (China)

Context

There are about 48 counties in the Asia-Pacific (AP) region. Many countries in the region have invested considerable resources on improved geoid models. Recent progress in satellite altimetry greatly increases coastal marine gravity accuracy. Satellite remote sensing data have been used to generate digital elevation models that are needed for geoid modeling. Many countries now increase their GNSS/leveling observation campaigns to collect data to assess and to control the qualities of gravimetric quasi/geoid models. All such datasets allow to improve geoid models in the Asia Pacific region.

Terms of Reference and Objectives

This sub-commission is a continuation of the previous sub-commission and will continue to promote gravity data collection, geoid processing and evaluating techniques, and geoid applications in the Asia-Pacific region. In particular, coastal marine gravity will be improved by recent altimetry data.  We will organize workshops to exchange data and techniques of geoid modeling and assessing.

Program of Activities

1. Gravity and Related Data
• share available gravity data  
• share available DEMs along common borders  
• combine resources for terrestrial gravity surveys along common borders
• promote regional airborne gravity surveys 
• determine improved coastal gravity anomalies from satellite altimetry
2. Gravimetric geoid and hybrid geoid quality control
   
• share GNSS/levelling and vertical deflection data for geoid quality control  
• promote regional GNSS/leveling and vertical deflection campaigns
• connect regional vertical datums
3. Education & Research
• organize meetings and workshops to improve modeling and evaluation techniques of gravimetric quasi/geoids, and to promote their application to height modernization and vertical datum connection.
• propose technical sessions in scientific and professional conferences
• propose matters of common concern/interest

Delegates

• Chair: Cheinway Hwang (China-Taipei)
• Vice-Chair: Wenbin Shen (China)
• Jay Hyoun Kwon (Korea)
• Will Featherstone (Australia)
• Koji Matsuo (Japan)
• Ami Hassan Md Din (Malaysia)
• Chalermchon Satirapod (Thailand)
• Kosashi Prijatna (Indonesia)
• Dinh Toan Vu (Vietnam)
• Ronaldo Gatchalian (Philippines)
• Ropesh Goyal (India)
• Matt Amos (New Zealand, corresponding member only)

SC 2.4f: Gravity and Geoid in Antarctica (AntGG)

Chair: Mirko Scheinert (Germany)
Vice-Chair: Fausto Ferraccioli (UK)

Terms of Reference

Antarctica is the region that still features the largest data gaps in terrestrial gravity. Global gravity field solutions suffer from the lack of terrestrial data in Antarctica as well as from the polar data gap originating from the orbit inclination of dedicated satellite gravity field missions (esp. GOCE with a polar data gap of 1,400 km diameter). 

The coverage with terrestrial (ground-based and airborne) gravity data in Antarctica has been improved during the last years. Efforts were successfully accomplished to publish a first Antarctic-wide gravity anomaly grid (Scheinert et al. 2016) and to record data over the polar data gap (Forsberg et al. 2017). However, the gravity data coverage in Antarctica is still insufficient. The data are heterogeneous and exhibit inconsistencies. Due to the vast extension of the Antarctic continent, its hostile environment and the difficult logistic conditions it is a long-lasting task to close the Antarctic data gaps in terrestrial gravity. 

AntGG shall pursue this objective and shall facilitate the necessary coordination to release an updated grid of terrestrial gravity data for Antarctica. Terrestrial gravity data are needed for the global high-resolution determination of the Earth’s gravity field and/or for a validation of global gravity field models, for a regional improvement of the Antarctic geoid and for geophysical inversion to improve our knowledge on the subglacial topography and inner structure of the Earth.

Thus, AntGG plays an important role to improve the cooperation between all interested scientists of geodesy and of neighbouring disciplines, mainly geophysics.

Program of Activities 

• Promoting the collection of surface and airborne gravity data in Antarctica;
• Promoting new gravity surveys in Antarctica, especially airborne gravimetry;
• Promoting the establishment  and (re-)measurement of reference gravity stations utilizing absolute gravity meters;
• Promoting the scientific exchange of latest developments in technology (esp. airborne gravimetry) and data analysis;
• Evaluation of existing and new surface and airborne gravity data, validation of global gravity field models in Antarctica;
• Investigation of optimum strategy for the combination of gravity data of different sources;
• Release of updated gridded gravity anomaly dataset(s) for Antarctica to the scientific public; 
• Organization of special workshop on airborne geodesy and geophysics (especially aerogravimetry) with focus on Antarctica;
• Focus group for all scientists interested in Antarctic gravity and geoid, and cooperation with similar data initiatives, especially within the Scientific Committee on Antarctic Research (SCAR);

Delegates

• Chair: Mirko Scheinert (Germany)
• Don Blankenship (USA)
• Alessandro Capra (Italy)
• Fausto Ferraccioli (UK)
• Christoph Förste (Germany)
• René Forsberg (Denmark)
• Larry Hothem (USA)
• Graeme Eagles (Germany)
• German L. Leitchenkov (Russia)
• Jaakko Mäkinen (Finland)
• Yves Rogister (France)
• Koichiro Doi (Japan)
• Michael Studinger (USA)

Corresponding Members

• Matt Amos (New Zealand)