1. Next steps after BPS inventory
Detlef Angermann
Deutsches Geodätisches Forschungsinstitut (DGFI-TUM) Technische Universität München The presentation is given on behalf of the GGOS Bureau of Products and Standards (BPS) BPS Staff: Detlef Angermann, Thomas Gruber, Michael Gerstl, Robert Heinkelmann, Urs Hugentobler, Laura Sánchez, Peter Steigenberger
Unified Analysis Workshop, July 10-12, 2017, Paris, France

2. GGOS Bureau of Products and Standards (BPS)
The BPS supports GGOS in its key goal to obtain consistent products describing the geometry, rotation and gravity field of the Earth.
Mission and objectives
to serve as contact and coordinating point for the homogenization of IAG standards and products;
to keep track of the adopted geodetic standards and conventions across all IAG components, and to initiate steps to close gaps and deficiences;
to focus on the integration of geometric and gravimetric parameters and to develop new geodetic products, needed for Earth sciences and society.

3. BPS Inventory
The BPS has compiled an inventory on standards and conventions used for the generation of IAG products:
Review of numerical standards;
Focus on IAG products: CRS/CRF, TRS/TRF, EOP, GNSS satellite orbits, gravity and geoid, heights;
Assessment of the present status, identification of gaps, provision of recommendations.
BPS inventory is published in the IAG Geodesist‘s Handbook 2016:
Angermann D., Gruber T., Gerstl M., Heinkelmann R., Hugentobler U., Sánchez L., Steigenberger P.: GGOS Bureau of Products and Standards: Inventory of standards and conventions used for the generation of IAG products. In: Drewes H., Kuglitsch F., Adám J. (Eds.) The Geodesist's Handbook Journal of Geodesy 90(10), , /s z, 2016

4. Numerical standards used within IAG
Tab.1: Numerical standards of conventional parameters (as given in different sources).
The IUGG/IAG Resolutions (1979) recommend that the GRS80 (defining parameters a, GM, J2 and ω) shall be used as reference for geodetic work.
Other sources for numerical standards are widely used in geodesy (e.g., IERS Conventions, EGM2008, GRACE and GOCE standards, …).
The IAG Resolution No. 1 (2015) introduces a new conventional W0 value of m2s-2.

5. Numerical standards used within IAG (continued)
Present situation concerning numerical standards:
Different sets of numerical standards are in use within IAG;
Different use of time and tide systems in geodetic products;
IAG Resolution No. 16 (1983) recommends the zero tide system for gravity field parameters and zero (=mean) tide system for geometry (not fulfilled, the conventional tide free system is used for ITRF);
The new conventional W0 value of m2s-2 (IAG Resolution No. 1, 2015) differs from the IERS value by about 25 cm (see W0 presentation in this session);
The current situation makes the consistent use of geodetic products difficult (in particular for users who are not specialized in geodesy);
The users must exactly know on which standards, time and tide systems the geodetic products are based; transformations are necessary if different standards are used.

6. Recommendations on numerical standards
The BPS inventory provides the following recommendations:
REC 1: The used numerical standards including time and tide systems must be completely documented for all geodetic products.
REC 2: The W0 value issued by the IAG resolution No. 1 (2015) should be used as the new reference value for geodetic work.
REC 3: The development of a new Geodetic Reference System GRS20XX based on best estimates of the major parameters is desired.

7. Activities and next steps on numerical standards
REC 1: Documentation of numerical standards
Complete information on numerical standards must be provided for geodetic products (e.g., for a correct use of products, to ensure consistency of combined products)
Various groups/entities are involved within IAG, e.g.,: IAG Services, CDDIS, GGOS Portal and WG Data and Information Systems, GGOS Bureaus BNO and BPS, …
Externally: Interoperability of IAG Service products, GGOS portal and external portals (e.g., GEOSS portal) (next session “Interoperability of Portals and Metadata”)
REC 2: W0 value issued by the IAG resolution No. 1 (2015)
This topic will be addressed in the presentation “A conventional value for the geoid reference potential W0 (L. Sánchez et al., this session)
REC 3: New Geodetic Reference System GRS20XX
See next slide for more details on this issue

8. Do we need a new GRS?
Some considerations from a paper published by J. Ihde et al. (see below):
The GRS80 represents the scientific status of the 1970s, new values for GM and a were recommended at IUGG 1991;
New best estimates should be computed for the complete set of fundamental parameters of a new level ellipsoid (as done for the GRS80);
The new W0 value (2015) could be used as a defining parameter for a new GRS, the semi-major axis a would then become a derived parameter;
If the computation of a new GRS is decided, an IAG WG should prepare and propose a full consistent set of parameters in the next future (e.g. for IUGG 2019);
In 2016, IAG has installed the JWG “Establishment of the GGRF”.
Ihde J., Sánchez L., Barzaghi R., Drewes H., Foerste Ch., Gruber T., Liebsch G., Marti U., Pail R., Sideris M.: Definition and proposed realization of the International Height Reference System (IHRS). Surveys in Geophysics 38(3), , /s , 2017

9. Product-based review (chapter 4 of BPS inventory)
4.1 Celestial reference systems and frames
4.2 Terrestrial reference systems and frames
4.3 Earth Orientation Parameters (EOP)
4.4 GNSS satellite orbits
4.5 Gravity and geoid
4.6 Height systems and their realizations
GGOS Focus Area
Unified Height System

10. IERS Products: ICRF, ITRF and EOP
BPS inventory provides 3-4 recommendations for each product.
Two general recommendations of the BPS inventory are given below:
- Consistency of CRF, TRF and EOP (IUGG Resolution No. 3, 2011)
- The processing standards should be consistently applied by the IGS, ILRS, IVS, IDS
and their analysis centers
Ongoing activities of the IERS and the technique-specific Services (e.g., Workshops of the Services, Unified Analysis Workshop).
IAU is involved concerning the celestial reference system and frame (e.g., IAU Division A Working Group “Third Realization of the ICRF”).
There is a interaction between the IERS and GGOS concerning standards (BPS), station networks and co-locations (BNO), and simulations (PLATO).

11. Impact of different EOP interpolation methods
As an example, this figure shows the differences between a cubic window and a piecewise linear interpolation (M. Gerstl, DGFI-TUM)
Impact for the x- and y-pole coordinates of the IERS C04 series:
Differences between both interpolation methods reach 0.1 mas (~3 mm)

12. GNSS satellite orbits, gravity and geoid, and heights
GNSS satellite orbits (BPS inventory, section 4.4)
- Responsibility of the IGS
- Presentation “SINEX satellite metadata format”, O. Montenbruck et al., this session
Gravity and geoid (BPS inventory, section 4.5)
- Responsibility of the IGFS
- Updated IGFS website (igfs.topo.auth.gr), including a dedicated products portal
for downloading IGFS data and products
- Many GGMs are available at the ICGEM website, a conventional GGM may be useful
Height systems and their realizations (BPS inventory, section 4.6)
- Focus Area “Unified Height System”
- IAG JWG “Strategy for the realization of the IHRS”
- Presentation “A conventional value for the geoid reference potential W0”,
L. Sánchez et al., this session

13. First proposal for the IHRF reference network (April 2017)
Proposed by: GGOS Focus Area „Unified Height System“ (Chair: Laura Sánchez)
~ 250 IHRF stations co-located with geometric techniques, absolute gravity and tide gauges

14. Summary of BPS tasks and next steps
BPS tasks (as specified in the BPS Implementation Plan ):
to continue the work regarding standards and conventions (ongoing activities to address the recommendations given in the BPS inventory);
to focus on the integration of geometric and gravimetric observations and to support the development of integrated products (e.g., GGRF, IHRF, atmosphere products);
to contribute to GGRF activities (e.g., IAG representation for key area: „Data Sharing and Development of Geodetic Standards“ );
to strengthen the interaction with external stakeholders (e.g., ISO, IAU);
to initiate steps to identify the user needs and requirements for geodetic products (with the GGOS Science Panel and the IAG Services);
to contribute to define essential geodetic variables and to perform a gap analysis (see GEO work plan) (as proposed by the GGOS Science Panel).

15. Recommendations and points for discussion
Recommendations on numerical standards:
REC 1: The used numerical standards including time and tide systems must be completely documented for all geodetic products.
REC 2: The W0 value issued by the IAG resolution No. 1 (2015) should be used as the new reference value for geodetic work.
REC 3: The development of a new Geodetic Reference System GRS20XX based on best estimates of the major parameters is desired.
Homogenization and documentation of processing standards
Unified processing standards are essential for consistent products
How far should we go with such a unification?
How should the processing standards be documented (e.g., SINEX files, AC log files, standardized form, …)?

16. Backup slides

17. GGOS Organizational Structure
External
Stakeholders
New Focus Area: Geodetic Space Weather Research

18. BPS Organizational Structure
The BPS is hosted by DGFI-TUM and IAPG of Technical University of Munich
Director: Detlef Angermann, deputy director: Thomas Gruber
BPS Staff [unchanged]:
- geometry, orbits, TRF: D. Angermann, U. Hugentobler, P. Steigenberger (assoc. member, DLR)
- Earth orientation, CRF: M. Gerstl, R. Heinkelmann (IAU representative, GFZ)
- gravity, geoid, heights: T. Gruber, L. Sánchez
GGOS entities associated to the BPS [no change since 2016]:
- Committee on Earth System Modelling (Chair: M. Thomas)
- WG “ITRS Standards for ISO TC 211” (Chair: C. Boucher)
- JWG “Establishment of the GGRF” (Chair: U. Marti)
BPS representatives (IAG Services and other relevant entities) [next slide]

19. Representatives of IAG Services and other entities

20. BPS Implementation Plan 2017-2018
Planned schedule of BPS communications and operational bureau business for 2017 and 2018
2017
2018
GGOS communications with BPS participation
Coordinating Board meetings x
Consortium meetings
EC telecons (monthly)
CO/BNO/BPS/SP (quarterly)
Reporting (1-page reports)
Operational BPS bureau business
Internal BPS meetings
BPS Board meetings
Reporting of BPS entities
Monitoring progress

21. Committee “Contributions to Earth System Modelling” Chair: Maik Thomas (GFZ Potsdam)
The major long-term goal is the establishment of a physically consistent modular system of near surface dynamics that can be simultaneously applied to all geodetic observables.
Planned activities for 2017/2018:
to introduce consistent numerical approaches for processes related to mass loading and self-attraction into system model components;
to develop a strategy for the implementation of data assimilation algortihms into dynamically coupled model approaches;
feasibility studies for the provision of uncertainties and error estimates of model predictions;
preparation of level 2 products by combining gravity field observations and process simulations.

22. Working Group “ITRS Standards for ISO TC 211” Chair: Claude Boucher (France)
The mission of this WG is to coordinate the IAG community in the support of the development of the ISO standard on ITRS. A proposal to develop a standard on ITRS has been approved by TC 211 in 2016.
Objectives:
to establish the list of IAG contributors to the work of the WG;
to collect comments and proposals on any draft documents provided by the ISO TC 211 / 19161;
to establish a glossary of geodetic terms in relation with the scope of the WG.

23. JWG “Establishment of the GGRF” Chair: Urs Marti (Switzerland)
This JWG will work on the establishment and coordination of the geometric reference frame, the global height system, the global gravity network and their temporal changes.
Ongoing activities and planned actions for 2017/2018:
clarify the role between the UN-GGIM WG and the IAG WG;
intensify the contacts to IERS and IAU for the calculation of the parameters of a new GRS;
define the reference stations of a network of the IHRS and a global gravity network;
study the influence of the permenant tide system on various geodetic quanitites (J2, f, W0, ɤ, Δg, …).

24. BPS Inventory