ggim.un.org Positioning geospatial information to address global challenges Global and National Geodetic Reference Frames: how they are connected and why they are needed? Zuheir ALTAMIMI Institut National de l’Information Géographique et Forestière, France Vice-President, International Association of Geodesy

ggim.un.org Positioning geospatial information to address global challenges The Global Geodetic reference Frame (GGRF) The GGRF includes various components…. Focus here: –The geometric part of the GGRF that allows precise positioning on the Earth surface –Global: The International Terrestrial Reference Frame (ITRF) –National : Access to the ITRF using GNSS technology Over 80% of the countries who responded to the UN-GGIM geodetic questionnaire declared ITRF and GNSS data to be highly critical for them.

ggim.un.org Positioning geospatial information to address global challenges Societal and Scientific Questions (1/2) Where am I, accurately, on Earth ? How to plan for territory & land management ? –Construction, mining, civil engineering, National boundaries,… How to locate areas and people at risk ? –Natural disasters: Earthquakes, Tsunamis & flooding, … How to ensure that geospatial data are inter-operable within a country, a region & globally ? How to accurately navigate between places on Earth, Oceans & Space ? But: How to accurately determine point positions on the Earth surface that is constantly deforming?

ggim.un.org Positioning geospatial information to address global challenges Societal and Scientific Questions (2/2) How the Earth is deforming ? –Tectonic plate motion –Land uplift & subsidence –Natural Hazard: Earthquake dislocations Post-seismic deformations, Volcano eruptions… –Ice melting –Sea level rise & variations → climate change & global warming

ggim.un.org Positioning geospatial information to address global challenges Answers Space Geodesy (Global by nature) is the science that provides accurate measurement & mathematical tools: –Positioning (location-based) –Quantification of Earth Changes in space & time –High precision Global Geodetic Reference Frame is needed Access to the GGRF by all nations is also needed To ensure inter-operability of geospatial data (global by nature), global and national reference frames must be interconnected ==> Technically very easy But how do we do that ?

ggim.un.org Positioning geospatial information to address global challenges Quantification of changes in space & time of the 3 fundamental properties of the Earth : its form (i.e. deformations), its gravity field & its rotation in space SLR VLBIGNSS/GPSDORIS Geodetic Instruments Space Geodesy

ggim.un.org Positioning geospatial information to address global challenges The Earth is constantly deforming Despite this complexity, positions on the Earth surface are determined in millimeters The satellite & its signal are disturbed by many phenomena

ggim.un.org Positioning geospatial information to address global challenges Global: Current Geodetic Networks VLBI SLR GNSS DORIS

ggim.un.org Positioning geospatial information to address global challenges The ITRF Z Y X Provided by the International Association of Geodesy (IAG) and its technique services. Freely available To all users.

ggim.un.org Positioning geospatial information to address global challenges The ITRF Chain: an International Cooperation Observations & Data Collection Data analysis & Product Generation per Technique Technique Unification & ITRF generation NMAs Space Agencies Universities Research Groups from: NMAs, Space Agencies & Universities USERS Schematic illustration of the chains leading to the ITRF generation

ggim.un.org Positioning geospatial information to address global challenges Why Multiple Techniques for the ITRF ? VLBI & SLR: –Fundamental for an accurate mathematical definition of the ITRF –Poor Geometry between North and South DORIS: for satellite orbit determination GNSS: Is the tool today to access the global ITRF by the regions and the countries

ggim.un.org Positioning geospatial information to address global challenges ITRF: GNSS Network Key messages: Data Sharing: GNSS data freely available to all users around the world Backbone link of National Reference Frames to the global ITRF

ggim.un.org Positioning geospatial information to address global challenges Examples of ITRF GNSS densifications Key messages: Data Sharing: GNSS data freely available to all users around the world Note Gaps in Africa, South America and South East Asia > 2500 GNSS stations: data freely available

ggim.un.org Positioning geospatial information to address global challenges How to connect a National Reference Frame to the ITRF? Build geodetic infrastructure using GNSS technology, enabling: Modern, more accurate and less costly national reference frame Easy to maintain than old classical geodesy: like small Ferrari vs heavy truck Easy access to the ITRF (see next) ==> Economic benefit Enhance capacity building & international cooperation in Geodesy for knowledge transfer & know how

ggim.un.org Positioning geospatial information to address global challenges AFREF Example Distribution of processed sites. Red symbol indicates sites used in the alignment to ITRF How to connect a National Reference Frame to the ITRF?

ggim.un.org Positioning geospatial information to address global challenges AFREF sites processed Distribution of AFREF sites processed. Note gap from Angola through Congo, Sudan and across North Africa.

ggim.un.org Positioning geospatial information to address global challenges Summary The ITRF underpins critical scientific and societal applications  Economic benefits It needs enhancement and long-term sustainability National Reference Frame: –An obligation by law –Easy access to the global ITRF using GNSS: Less costly, easy to maintain & more precise –Gaps in GNSS Networks and areas at risk –Need for Capacity Building in Geodesy Global level: ITRF accuracy is highly critical: –Inhomogeneous distribution of Core sites, Especially in areas of developing countries –Aging instruments –Based on the “best effort” principle

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