The accurate determination of the gravity field and its temporal variations is one of the three fundamental pillars of modern geodesy (besides of geometry/kinematics and Earth rotation). This is essential for applications in positioning and navigation, civil engineering, metrology, geophysics, geodynamics, oceanography, hydrology, cryospheric sciences and other disciplines related to the Earth’s climate and environment. IAG Commission 2 was established at the IUGG in Sapporo in summer 2003 for promoting, supporting, and stimulating the advancement of knowledge, technology, and international cooperation in the geodetic domain associated with Earth’s gravity field.
Since most of the scientific themes are of long-term interest, large parts of the structure of Commission 2 are continued on the same basis as in the previous period 2011-15. Main focus points for the present period 2015-19 are related to the IUGG and IAG resolutions adopted at the XXVI IUGG General Assembly 2015 in Prague, addressing the topics global geodetic reference frames, future satellite gravity mission constellations, and the role of oceans in the climate system (IUGG), as well as definition and realization of an International Height Reference System (IHRS) and the establishment of an absolute gravity reference system (IAG). The structure of Commission 2 has been adopted to address these objectives and tasks, and joint working and study groups have been implemented accordingly.
Commission 2, at the start of the new period, consists of six sub-commissions (SCs), plus several Joint Study Groups (JSG) and Joint Working Groups (JWG), all of them jointly with other Commissions and/or services. The sub-commissions cover the following scientific topics:
- terrestrial, airborne, ship borne gravimetry and relative/absolute gravity networks;
- methodology for geoid and physical height systems;
- satellite gravity missions;
- regional geoid determination;
- satellite altimetry;
- gravity and mass transport in Earth system
Commission 2 has strong links to other commissions, GGOS, IGFS, ICCT and other components of IAG. Connections to these components are created through joint working groups (JWGs) and joint study groups (JSGs) that provide a cross-disciplinary stimulus for work in several topics of interest to the commission, and the joint organization of meetings.
The main tasks of Commission 2 in the period 2015-19 are among others:
- Establishment of an absolute gravity reference system to replace the International Gravity Standardization Net 1971 (IGSN71), which no longer fulfills the requirements and accuracy of a modern gravity reference; especially to include time-dependent gravity variations
- Supporting the realization of an International Height Reference System (IHRS)
- Supporting the realization of an Global Geodetic Reference System (GGRS)
- Analysis of current and future satellite data (CHAMP, GRACE, GOCE, GRACE-FO) and the release of improved global Gravity field models (satellite only models and in combination with terrestrial data and satellite altimetry)
- Promoting future gravity mission constellations for assuring the continued monitoring of global gravity and mass transport processes in the Earth system
- Assuring the future of the comparison campaigns of absolute gravimeters
- Investigating modern relativistic methods and geodetic metrology with special focus on gravity field and height determination
- Fostering regional gravity and geoid determination and integration of regional models into a global reference
- Assisting the regional sub-commissions in establishing contacts and in acquiring data
- Understanding of physics and dynamics of the Earth sub-systems and mass transport processes in the Earth system
- Providing contributions to operationalization of mass transport modelling and stimulation of new applications
- Fostering communication with user communities
- Assisting the IGFS and its components in improving their visibility and their services
The necessary WGs and SGs can be established at any time and they can be dissolved when they reached their goals or if they are not active.
The main objectives of Commission 2 are as listed in the IAG by-laws:
- Terrestrial, marine and airborne gravimetry
- Satellite gravity field observations
- Gravity field modeling
- Time-variable gravity field
- Geoid determination
- Satellite orbit modeling and determination
- Satellite altimetry for gravity field modeling
The Gravity Field Commission fosters and encourages research in the areas of its sub-entities by facilitating the exchange of information and organizing Symposia, either independently or at major conferences in geodesy. The activities of its sub-entities, as described below, constitute the activities of the Commission, which will be coordinated by the Commission and summarized in annual reports to the IAG Bureau.
The principal symposia that will be organized jointly by Commission 2 and the IGFS in the next period will be held in Thessaloniki in September 2016, and in 2018 (location TBD). The other two symposia where a Commission 2 meeting will be held are the IAG Scientific Assembly 2017 in Kobe, Japan, and the IUGG General Assembly 2019 in Montréal.