NATIONAL REPORT OF THE FEDERAL REPUBLIC OF ... - IAG Office

see ILK et al. (2005b), MAYER-GÜRR et al. (2006), MAYER-
GÜRR (2006); Integration approach, see NOVAK et al.
(2006); Multiscale modelling, see FENGLER et al. (2004a)
(2005, 2007), SCHMIDT M. et al. (2006). Several solutions
have been computed from the GRACE data (see chapter
on global models).
GOCE: As the GOCE mission is not yet in orbit, work
concentrated on preparations for using the new type of
gravity gradient observations for global gravity field
modelling, on calibration & validation of the GOCE gravity
gradient data and on required computational efforts for a
global model up to degree and order 250. For more details
on the GOCE mission and products, see GRUBER &
RUMMEL (2006), GRUBER et al. (2006) (2007), KOOP et al.
(2007), RUMMEL et al. (2003b) (2004) (2007). The major
work was focused on using GOCE data for gravity field
recovery. Different approaches as well as techniques to
filter the band-limited gradient observations have been
developed and implemented. For more details see: ABRI-
KOSOV & SCHWINTZER (2004), ABRIKOSOV et al. (2006)
(2007a) (2007b), BAUR & SNEEUW (2007), EICKER et al.
(2005) (2006), FÖRSTE et al. (2007), KARGOLL (2003, 2005),
MAYER-GÜRR et al. (2003b) (2003c), PAIL et al. (2005)
(2007a) (2007b) (2007c), SCHUH W.D. (2003a) (2003b),
SCHUH W.D. et al. (2007), WERMUTH et al. (2003, 2006),
WILD & HECK (2004) (2005). As the computational effort
to determine a GOCE gravity field solution is extraordinary,
another focal point was the derivation and implementation
of efficient algorithms. More details can be found in:
ALKHATIB (2003), ALKHATIB & SCHUH (2007), AUSTEN et
al. (2006), AUSTEN & KELLER (2006), BAUR & GRAFAREND
(2005, 2006), BAUR et al. (2006), BAUR & KUSCHE (2007),
BOXHAMMER (2003) (2006), BOXHAMMER & SCHUH (2006),
GUNDLICH et al. (2003), KOCH et al. (2004), KOCH (2005).
Gravity gradients observed in space by the GOCE mission
are internally and externally calibrated. The calibration is
crucial for the quality of the final global gravity field
models. Several papers address methods and tools either
to calibrate or to validate the observed gravity gradients.
See: BOUMAN et al. (2005), DENKER (2003), DENKER et al.
(2003), DIETRICH et al. (2004), JARECKI & MÜLLER (2003),
JARECKI et al. (2006), MÜLLER (2003a), MÜLLER et al.
(2003b) (2004), STUMMER (2006), TOTH et al. (2005a)
(2005b), WOLF et al. (2003) (2004) (2005), WOLF (2006).
Global Models
The following global gravity field models have been
published by groups in Germany (some in cooperation with
other international partners):
– EIGEN-2 : CHAMP, GeoForschungsZentrum Potsdam,
REIGBER et al. (2003d);
– EIGEN-CHAMP03S: CHAMP: GeoForschungsZentrum
Potsdam, REIGBER et al. (2005b);
– EIGEN-GRACE02S: GRACE, GeoForschungsZentrum
Potsdam, REIGBER et al. (2005a);
– EIGEN-CG01C: GRACE & surface data, Geo-
ForschungsZentrum Potsdam, REIGBER et al.(2006b);
T. Gruber: Global Gravity Field Modelling 51
– EIGEN-CG03C: GRACE & surface data, Geo-
ForschungsZentrum Potsdam;
– EIGEN-GL04S: GRACE, LAGEOS, GeoForschungs-
Zentrum Potsdam;
– EIGEN-GL04C: GRACE, LAGEOS & surface data,
GeoForschungsZentrum Potsdam;
– ITG-CHAMP01: CHAMP, Universität Bonn, MAYER-
GÜRR et al. (2005a), ILK et al. (2005a);
– ITG-GRACE02s : GRACE, Universität Bonn, MAYER-
GÜRR et al. (2007);
– SWITCH-03: CHAMP, Technische Universität Kaiserslautern,
FENGLER et al. (2004b);
– TUM-1s: CHAMP, Technische Universität München,
GERLACH et al. (2003a);
– TUM-2sp: CHAMP, Technische Universität München,
FÖLDVARY et al. (2005);
– TUM-2s: CHAMP, Technische Universität München.
Model Validation
The validation of global gravity field models by means of
independent data and observations becomes more and more
important, because the mission data from CHAMP, GRACE
and GOCE provide fields with unprecedented accuracy. In
opposite, gravity field solutions from these missions can
also be applied for validating ground data. GRUBER (2004)
summarizes classical concepts, which can be applied for
validating satellite derived global gravity field models. ILK
& LÖCHER (2005c), LÖCHER & ILK (2005) (2007) apply
energy balance equations for validating gravity field models
and orbits. KLOKOCNIK et al. (2005) and ROMANOVA et al.
(2007) use satellite altimeter data via the crossover technique
and ocean state estimation procedures, respectively,
for validating global gravity field models by means of
independent data over the oceans. Finally, ROLAND &
DENKER (2003) (2005b) (2005c) and ROLAND (2005a) use
global gravity field models for validating observed gravity
data on ground. All methods require the application of filter
techniques in order to enable the comparison of bandlimited
global models (by a truncated spherical harmonic
series) to observed ground data containing the full signal.
Future Prospects
A few studies on the requirements and instrumentation of
future gravimetry satellite missions have been performed
during the reporting period. These studies were focused on
the identification of the scientific requirements for the
different science applications, see AGUIRRE-MARTINEC &
SNEEUW (2003), FLURY & RUMMEL (2005) and Sneeuw et
al (2005b). Further studies recently have been initiated,
which will identify more details of potential future mission
scenarios and possible instrumentation configurations.
During the next couple of years the analysis of the GRACE
mission data as well the availability of the GOCE gravity
gradients will drive the further development in this area.
It can be expected that new sets of gravity field models
either from GRACE or GOCE only and from combinations