Session G08: The Future of Geodetic Networks

New Scientific Challenges: The Global Geodetic Observing System (GGOS)

M. Rothacher, R.E. Neilan, H.-P. Plag

Department 1 Geodesy and Remote Sensing, GeoForschungsZentrum Potsdam (GFZ),
Telegrafenberg A17, D-14473 Potsdam, Germany

Jet Propulsion Laboratory MS 238-540, 4800 Oak Grove Drive, Pasadena,
CA 91109, USA

Nevada Bureau of Mines and Geology / MS 178, University of Nevada,
Reno Nevada 89557-0088, USA

The helplessness we feel in view of natural disasters demonstrates very clearly
that at present our knowledge of the Earth's complex system and our tools for
the timely detection of potentially disastrous events are rather limited. The space
geodetic community with its Global Geodetic Observing System (GGOS)
--- the project of the International Association of Geodesy officially established
in Budapest in 2003 --- can make, though, important contributions to the growing monitoring
capacity for these risks to reduce the impact of these events.

The twelve existing IAG services are the crucial basis for the generation of
relevant products for Earth monitoring. In order to reach the ambitious
goals envisaged by GGOS, however, considerable challenges have to be faced
by the services and the geodetic community and substantial progress
has to be made on four different levels of complexity:

Level 1: the raw geodetic observations from the space techniques and satellite missions
(altimetry, gravity, atmosphere, ...) may be consider GGOS products of level 1.
To strive for uninterrupted, high-quality data series transmitted
in near real-time or real-time to allow for fast reaction time, covering time spans
of decades for stability, will require a tremendous international joint effort.

Level 2: individual service products for the shape and deformation of the
Earth's surface (including the oceans), Earth's orientation and rotation, and the Earth's
gravity field and its temporal variations, and, in addition, the atmospheric information
derived from ground-based and space-borne measurement techniques like GNSS. Consistent time
series of officially combined products should become available from each observation technique
covering the entire time history of the technique to allow for the detection of long-term trends.

Level 3: products resulting from a combination of all the space geodetic
techniques, e.g., consistent combined products generated by the IERS (ITRF, EOP series, ...)
and the IGFS (gravity field series, ...). These activities have barely started yet and we still
have a long way to go when thinking, e.g., of a rigorous combination of geometry, Earth rotation
and gravity.

Level 4: the inter-disciplinary level of consistent modelling and
interpretation of the processes in the Earth's system, making use of level 3 products,
global geophysical fluid information, relationships between surface deformation,
variations in Earth rotation and variations in the gravity field.
The final goal would be to obtain comprehensive global Earth models that can
assimilate, e.g., global surface deformations, information about mass
transport and exchange.

To reach these goals of GGOS the IAG commissions, services and brilliant young
scientists all over the world are encouraged to join this endeavor.