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

Information System contains 281,000 gravity points covering
entire Germany and border-zone areas to neighbouring
countries. 157,000 data points belong to companies from
the German hydrocarbon industry. The system is open to
the public via the internet.
4. Projects and Results
Within the framework of the “European Gravity and Geoid
Project (EGGP)”, a project within Commission 2 of the
International Association of Geodesy (IAG), several new
European geoid and quasigeoid models were derived and
a final version shall be presented at the IUGG General
Assembly 2007 in Perugia. The project (also known as
CP2.1) is chaired by H. DENKER, IfE, Hannover. Progress
reports were given anually at scientific meetings in Porto
2004 (DENKER et al. 2005, DENKER 2005b), Austin 2005
(DENKER 2005d), and Istanbul 2006 (DENKER et al. 2007).
Further informations related to the EGGP can be found in
DENKER et al. (2003a and 2004) and DENKER (2004, 2006a,
2006b). Due to the confidentiality of many data sets, only
one data and computing center was set up at IfE in
Hannover. The presently available results indicate an
accuracy potential of the gravimetric (quasi)geoid models
in the order of 3 – 5 cm at continental scales and 1 – 2 cm
over shorter distances up to a few 100 km, provided that
high quality and resolution input data are available. This
is a very significant improvement compared to the last
published (quasi)geoid model EGG97, the key elements
being improved terrestrial and satellite gravity field data
from the CHAMP and GRACE missions (e.g., DENKER
2005b and 2005c).
In connection with the EGGP, a consistent marine gravity
data set was derived (DENKER and ROLAND 2005, ROLAND
2005), the merging of ship and altimetric data was studied
(ROLAND and DENKER 2005c), and contributions were made
to the cross-validation of terrestrial and satellite gravity data
(ROLAND and DENKER 2003 and 2005a). In addition, the
collected terrestrial data sets were utilized for the computation
of gravity gradients at satellite altitude with regard to
the coming GOCE satellite mission (DENKER 2003A,
MÜLLER et al. 2004b, WOLF et al. 2003, WOLF and DENKER
2005, WOLF 2007). Linked to the EGGP are also the
activities within the EUVN-DA project, an initiative to
collect a dense network of GPS and levelling control points
in Europe (KENYERES et al. 2006 and 2007).
A corresponding geoid project was established for Antarctica
within IAG Commission 2. The project “Antarctic
Geoid (AntGP)” (CP2.4), chaired by M. SCHEINERT, TU
Dresden, is aiming at the improvement of the terrestrial
gravity coverage and geoid in Antarctica. Intensive activities
took place in order to get access to already existing data
sets as well as to link the AntGP goals to planned surveys,
especially within the framework of the International Polar
Year 2007/2008. A close relation was maintained to the
project “Physical Geodesy” (chaired by M. SCHEINERT and
A. CAPRA, Italy) within the SCAR GIANT program.
Reports were given regularly to the IAG and on dedicated
conferences (e.g. SCHEINERT 2005). A case study for
regional geoid determination in Antarctica was presented
H. Denker: Regional Gravity Field Modelling 59
for the region of the Prince Charles Mountains and Lambert
Glacier, East Antarctica (SCHEINERT et al. 2007).
Since 2003, absolute gravity measurements were performed
in Scandinavia at about 30 stations co-located with permanent
GPS sites. The observations were carried out by four
groups including IfE in Hannover (TIMMEN et al. 2005 and
2006, PETTERSEN et al. 2005a and 2005b). The aim of the
project is to study glacial isostasy effects and to provide
ground truth data for the GRACE satellite gravity mission
(MÜLLER et al. 2003a, 2003c, 2004c, 2005a, 2005b, 2006a,
2007).
Several investigations were carried out with respect to the
upcoming GOCE satellite gradiometer mission (see also
other sections of the present report); the activities concern
the GOCE processing algorithms (KOOP and MÜLLER
2004), error studies (e.g., WOLF 2007, WOLF and MÜLLER
2004, WOLF 2006), calibration and validation topics
(BOUMAN et al. 2005, DENKER et al. 2003c and 2003d,
MÜLLER et al. 2003b and 2006b, TOTH et al. 2005, WOLF
2004), temporal variations in the GOCE data (JARECKI et
al. 2005), quality assessment procedures (JARECKI et al.
2006), and a regional combination and validation experiment
in Germany with heterogeneous data (LUX et al. 2006,
VOIGT et al. 2006).
In a joint effort, the Bundesamt für Kartographie und
Geodäsie (BKG), Frankfurt am Main, and IfE, Hannover,
developed a new model for the height reference surface
(quasigeoid) in Germany, which now serves as a standard
for the conversion between GPS ellipsoidal heights and
normal heights. BKG and IfE did independent computations
based on two different methods, both relying on the
remove-restore technique. The input data were point gravity
observations with a spacing of a few km, a digital terrain
model with a block size of 50 m, a global geopotential
model as well as GPS and levelling control points. Due to
insignificant differences between the two independent
solutions, both results were simply averaged, yielding the
final GCG05 model. The evaluation of this model with
independent GPS and levelling points suggests an accuracy
of about 1 to 2 cm. For details see DENKER et al. (2003B),
IHDE et al. (2006a and 2006b), LIEBSCH et al. (2006),
SCHIRMER ET AL. (2006), and IHDE et al. (2007).
Moreover, German scientists contributed to geoid studies
in Iran (ARDALAN and GRAFAREND 2004) and Turkey
(ÜSTÜN et al. 2005, EROL et al. 2007a and 2007b). Finally,
the previous national report on regional and local gravity
field modelling activities can be found in DENKER (2003b).
References
ARDALAN A.A., GRAFAREND E.: High-resolution regional geoid
computation without applying Stokes’s formula: a case study
of the Iranian geoid. Journal of Geodesy 78, 138-156, 2004.
BOUMAN J., KOOP R., HAAGMANS R., MÜLLER J., SNEEUW N.,
TSCHERNING C.C., VISSER P.: Calibration and Validation
of GOCE Gravity Gradients. In: F. Sanso (ed.): A Window
on the Future of Geodesy – Sapporo, Japan, June 30 - July
11, 2003, IAG Symp., Vol. 128, 265-270, Springer Verlag,
Berlin, Heidelberg, New York, 2005.