Note to the GEO Plenary from IAG/GGOS
=====================================

The International Association of Geodesy (IAG) is implementing the
Global Geodetic Observing System (GGOS). GGOS is IAG's response to
the IUGG Resolution No. 3, taken at the International Union of
Geodesy and Geophysics (IUGG) General Assembly in 2003 in Japan.

GGOS is based on the geometrical and gravitational monitoring of
the Earth with geodetic techniques: The IERS (International Earth
Rotation and Reference Systems Service) Terrestrial Reference
Frame (ITRF) and the rotational motion of our planet is derived
from radio-astronomical, satellite and lunar laser ranging, and
GNSS (Global Navigation Satellite System including DORIS)
observations; the sea surface topography is derived from satellite
altimetry; the gravity field of the Earth is determined from
dedicated satellite missions like CHAMP, GRACE, and GOCE.

Tremendous progress was made in recent years, despite the fact
that most of the effort is based "only" on a voluntary cooperation
of geodesy-related entities (including national surveys, research
establishments, universities): The ITRF is today realized by about
200 observing sites with cm-accuracy in position and sub-mm/year
accuracy in station velocity. Our knowledge of the global gravity
field approaches the cm-level in the geoid (equipotential surface
near the Earth surface).

GGOS puts these activities into one coherent frame. GGOS defines
the products and their target accuracies, the network composition,
and it identifies the satellite missions necessary for a long-term
geodetic monitoring of the planet Earth. Naturally, the networks
and missions have to meet the scientific and societal needs of the
future.

GGOS is extremely relevant for science and society, because it
provides the metrological basis for global change monitoring,
research, and possibly mitigation. The recent Sea Level Workshop
held in Paris 2006, sponsored also by GEO, emphasized the
importance of the geometric and gravitational reference frame as
the backbone for monitoring changes in ice sheets and sea level.

In view of the importance and the impact on scientific and
societal needs of the future IAG proposes the following resolution
for consideration to the GEO plenary:

RESOLUTION:

GGOS is viewed as the metrological basis for global change studies
and as the prerequisite to develop strategies to mitigate the
impact of global change (e.g., to mitigate the impact of sea level
rise).

GGOS is considered as a key element of the GEOSS.

[ IAG is urged to come up, within one year, with a concise plan for
geodetic Earth monitoring for the next two decades as a
contribution to the GEOSS. == Attempt to spped up the writing of the
GGOS2020 document ]