0.1.2. Working Group on Strategy for the Realization of the International Height Reference System (IHRS)

Joint Working Group (JWG) of

- GGOS,
- IAG Commission 2 (Gravity field),
- IAG Commission 1 (Reference Frames),
- IAG Inter-commission Committee on Theory (ICCT), and the
- International Gravity Field Service (IGFS).

This JWG is coordinated by the GGOS Focus Area Unified Height System.

Term: 2015 - 2019

Chair: L. Sánchez (Germany)

Members: J. Ågren (Sweden), M. Amos (New Zealand), R. Barzaghi (Italy), S. De Freitas (Brazil), W. Featherstone (Australia), T. Gruber (Germany), J. Huang (Canada), J. Ihde (Germany), G. Liebsch (Germany), J. Mäkinnen (Finland), U. Marti (Switzerland), P. Novák (Czech Republic), M. Poutanen (Finland), D. Roman (USA), D. Smith (USA), M. Véronneau (Canada), Y. Wang (USA), M. Blossfeld (Germany), J. Böhm (Austria), X. Collilieux (France), M. Filmer (Australia), B. Heck (Germany), R. Pail (Germany), M. Sideris (Canada), G. Vergos (Greece), C. Tocho (Argentina), H. Denker (Germany), D. Avalos (Mexico), H. Wziontek (Germany), M. Varga (Croatia), I. Oshchepkov (Russia), D. Blitzkow (Brazil), A.C.O.C. Matos (Brazil), J. Bouman (Germany), H.A. Abd-Elmotaal (Egypt), K. Matsuo (Japan), S. Claessens (Australia), R. Forsberg (Denmark), T. Jiang (China), V.N. Grigoriadis (Greece), D.A. Natsiopoulos (Greece), Q. Liu (Germany), M. Willberg (Germany), B. Erol (Turkey), M. Serkan Isik (Turkey), S. Erol (Turkey).


Motivation

The IAG Resolution No. 1 released during the IUGG 2015 General Assembly outlines five conventions for the definition of the International Height Reference System (IHRS). The definition is given in terms of potential parameters: the vertical coordinates are geopotential numbers (-Delta_WP = CP = W0 - WP) referring to the equipotential surface of the Earth's gravity field realized by the conventional value W0 = 62 636 853.4 m2s-2. The spatial reference of the position P for the potential WP = W(X) is given by coordinates X of the International Terrestrial Reference Frame (ITRF). This Resolution also states that parameters, observations, and data shall be related to the mean tidal system/mean crust.

At present, the main challenge is the realization of the IHRS; i.e., the establishment of the International Height Reference Frame (IHRF). It is expected that the IHRF follows the same structure as the ITRF: a global network with regional and national densifications, whose geopotential numbers referring to the global IHRS are known. According to the GGOS objectives, the target accuracy of these global geopotential numbers is 1 x 10-2 m2s-2. In practice, the precise realization of the IHRS is limited by different aspects; for instance, there are no unified standards for the determination of the potential values WP, the gravity field modelling and the estimation of the position vectors X follow different conventions, the geodetic infrastructure is not homogeneously distributed globally, etc. This may restrict the expected accuracy of 1 x 10-2 m2s-2 to some orders lower (from 10 x 10-2 m2s-2 to 100 x 10-2 m2s-2). Consequently, the next step is to outline the minimum set of fundamentals needed for a reliable and sustainable realization of the IHRS.

The primary requirement of the IHRF reference network is its collocation with:

  • fundamental geodetic observatories (to make feasible the connection between position vectors X, gravity potential W, international atomic time TAI, and absolute gravity g);
  • geometrical reference stations of different densification levels (presumable with GNSS to allow access to the IHRF also in remote areas);
  • reference tide gauges and local levelling networks (to precisely know the local geopotential numbers and to allow the global vertical datum unification);
  • gravity reference stations.


Objectives

The objectives of the WG on Strategy for the Realization of the International Height Reference System (IHRS) are:

  • To define the standards and conventions required to establish an IHRF consistent with the IHRS definition. A main issue is the high-precise modelling of the time-dependent changes of the vertical coordinate (which also reflect time variations of X and W).
  • To formulate minimum requirements for the IHRF reference stations.
  • To develop a strategy for collocation of IHRF reference stations with existing geometrical reference stations at different densification levels.
  • To identify the geodetic products associated to the IHRF and to describe the elements to be considered in the corresponding metadata.
  • To review the processing strategies for the determination of the potential values WP and to recommend an appropriate computation procedure based on the accuracy level offered by those strategies.
  • To review different approaches for the vertical datum unification and to provide guidance for the integration of the existing local height systems into the global IHRS/IHRF.

The activities of this WG are based on the results presented by previous work, in particular those of the IAG Inter-Commission Project 1.2: Vertical Reference Frames (conventions for the definition of World Height System, 2003 – 2011); GGOS Focus Area 1 Unified Height System (action Items for the unification height reference systems, since 2011); the ESA project “GOCE+ Height System Unification with GOCE” (2011-2014); the GGOS-BPS (inventory of standards and conventions used for the generation of IAG/GGOS products, since 2011); and the Working Group on Vertical Datum Standardization (2011-2015).


Expected results

The main result of this WG should be a document similar to the IERS conventions; i.e., a sequence of chapters describing the different components to be consider for the precise and sustainable realization of the IHRS and its practical utilization.


Business meetings

Business meeting at the GGHS2018 Symposium, Copenhagen, Denmark, September 18, 2018 (Meeting summary).

Business meeting at the IAG-IASPEI 2017 Joint Scientific Assembly, Kobe, Japan, July 31, 2017 (Meeting summary).

Business meeting at the GGHS2016 Symposium, Thessaloniki, Greece, September 21, 2016 (Meeting summary).


Publications

Ihde J., Sánchez L., Barzaghi R., Drewes H., Foerste Ch., GruberT., Liebsch G., Marti U., Pail R., Sideris M.: Definition and proposed realization of the International Height Reference System (IHRS). Surveys in Geophysics, 10.1007/s10712-017-9409-3, 2017

Sánchez L., Sideris M.G.: Vertical datum unification for the International Height Reference System (IHRS) . Geophysical Journal International 209(2), 570-586, 10.1093/gji/ggx025, 2017

Sánchez L., Martí U., Ihde J.: Le chemin vers un système de référence altimétrique global et unifié. Association Française de Topographie, Revue XYZ 150: 61-67, 2017

Sánchez L., Ågren J., Huang J., Wang Y.M., Forsberg R.: Basic agreements for the computation of station potential values as IHRS coordinates, geoid undulations and height anomalies within the Colorado 1 cm geoid experiment, 2018


Presentations

Sánchez L.: GGOS Focus Area Unified Height System: Status report, ongoing activities, outlook. GGOS Coordinating Board Meeting, Vienna, Austria, 2019-04-06

Sánchez L.: GGOS Focus Area Unified Height System: Status report, ongoing activities, outlook. GGOS Days 2018, Tskuba, Japan, 2018-10-03

Sánchez L., Sideris M.: Vertical Datum Unification for the International Height Reference System (IHRS). International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018-09-20

Sánchez L., Ågren J., Huang J., Véronneau M., Wang Y.M., Roman D., Vergos G., Abd-Elmotaal H., Amos M., Barzaghi R., Blitzkow D., Matos A.C.O.C., Denker H., Filmer M., Claessens S., Oshchepkov I., Marti U., Matsuo K., Sideris M., Varga M., Willberg M., Pail R.: Advances in the establishment of the International Height Reference Frame (IHRF). International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018-09-17

Wang Y.M., Forsberg R., Sánchez L., Ågren J., Huang J.: Report on Colorado geoid comparisons. International Symposium on Gravity, Geoid and Height Systems 2018 (GGHS2018), Copenhagen, Denmark, 2018-09-19

Sánchez L., Madzak M.: GGOS activities related to the implementation of the International Height Reference System (IHRS). European Geosciences Union General Assembly 2018, Vienna, Austria, 2018-04-10

Sánchez L.: GGOS Focus Area Unified Height System: Ongoing activities. GGOS Coordinating Board Meeting, Vienna, Austria, 2018-04-07

Sánchez L.: GGOS Focus Area Unified Height System: Report, ongoing activities, outlook. GGOS Days 2017, Vienna, Austria, 2017-01-01

Sánchez L., Denker H., Pail R., Lieb V., Huang J., Roman D., Ågren J., Amos M., Ihde J., Barzaghi R., Sideris M., Oshchepkov I., Blitzkow D., Matos A.C.O.C., Piñon D., Avalos D., Freitas S.R.C., Luz R.: A first approximation to the International Height Reference Frame (IHRF). Joint Scientific Assembly of the International Association of Geodesy and the International Association of Seismology and Physics of the Earth’s Interior (IAG-IASPEI 2017), Kobe, Japan, 2017-08-03

Mäkinen J.: The permanent tide and the International Height Reference System IHRS. Joint Scientific Assembly of the International Association of Geodesy and the International Association of Seismology and Physics of the Earth’s Interior (IAG-IASPEI 2017), Kobe, Japan, 2017-08-01

Vergos G.S., Tziavos I.N.: Establishing an IHRS reference station. Joint Scientific Assembly of the International Association of Geodesy and the International Association of Seismology and Physics of the Earth’s Interior (IAG-IASPEI 2017), Kobe, Japan, 2017-08-01

Sánchez L., Čunderlík R., Mikula K., Minarechová Z., Dayoub N., Šíma Z., Vatrt V., Vojtíšková M.: A conventional value for the geoid reference potential W0. Unified Analysis Workshop 2017 (UAW2017), Paris, France, 2017-07-12

Sánchez L., Ihde J., Pail R., Gruber T., Barzaghi R., Marti U., Ågren J., Sideris M., Novák P.: Towards a first realization of the International Height Reference System (IHRS). European Geosciences Union General Assembly 2017, Vienna, Austria, 2017-04-25

Sánchez L. Sideris M.G.: Vertical datum unification for the International Height Reference System (IHRS). European Geosciences Union General Assembly 2017, Vienna, Austria, 2017-04-27

Marti U., Sánchez L.: Le système de référence altimétrique global. Commission Géopositionnement, Conseil national de l’information géographique, Paris, France, 2017-03-15

Sánchez L., Ihde J., Pail R., Barzaghi R., Marti U., Ågren J., Sideris M., Novák P.: Strategy for the Realization of the International Height Reference System (IHRS). Symposium SIRGAS 2016, Quito, Ecuador, 2016-11-18

Sánchez L.: Invitación a la realización del Sistema de Referencia Internacional de Alturas (IHRS) en la Región SIRGAS (in Spanish). Meeting of the SIRGAS Directing Council, Quito, Ecuador, 2016-11-17

Sánchez, L. International Height Reference System (IHRS): Required measurements and expected products. GGOS Days 2016, Cambridge (MA), USA, 2016-10-26

Sánchez L., Ihde J., Pail R., Barzaghi R., Marti U., Ågren J., Sideris M., Novák P.: Strategy for the Realization of the International Height Reference System (IHRS). GGHS2016: International Symposium on Gravity, Geoid and Height Systems 2016, Thessaloniki, Greece, 2016-09-22

Sánchez L.: Working Group on the Strategy for the Realization of the International Height Reference System (IHRS): Brainstorming and definition of action items. Splinter meeting at the International Symposium on Gravity, Geoid and Height Systems 2016, 2016-09-21

Sánchez L.: GGOS Focus Area 1: Unified Height System: Present activities, GGOS Coordinating Board Meeting, TU Vienna, Vienna, Austria, 2016-04-16

Sánchez L., Ihde J., Barzaghi R., Drewes H., Foerste Ch., Liebsch G., Marti U., Sideris M.: Establishment of an International Height Reference System in the frame of GGOS. Symposium SIRGAS 2015, Santo Domingo, Dominican Republic, 2015-11-19

Ihde J., Sánchez L.: Physical Height and the GGRF, Earth Gravity Field and the GGRF, GGRF an Integrated Approach. GGOS Days 2015, Frankfurt a.M., Germany, 2015-10-22