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

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1. Modelling Techniques
Fundamentals of gravity field modelling are described in
the textbook published by TORGE (2003), while the textbook
from FREEDEN and MICHEL (2004) focuses on the
application of multiscale techniques in potential theory.
Moreover, multiscale techniques were studied with regard
to geoid modelling (FEHLINGER et al. 2007, FENGLER et al.
2004a, FREEDEN et al. 2007, FREEDEN and SCHREINER 2006,
KUROISHI and KELLER 2005), global gravity field modelling
(FENGLER et al. 2004b, HESSE 2003), and temporal gravity
field variations (FENGLER et al. 2005 and 2007). In addition,
advanced gravity field modelling topics and results are
presented in the dissertation theses from GERLACH (2003),
HIRT (2004), ROLAND (2005) and WOLF (2007).
Different approaches for terrain and mass reductions are
discussed in HECK and SEITZ (2007) and KUHN and SEITZ
(2005). The use of terrain reductions in connection with
satellite gradiometry is investigated in HECK and WILD
(2005) and WILD and HECK (2004 and 2005). Band-limited
topographic effects for application in airborne gravimetry
and subsequent geoid determination are studied in NOVAK
et al. (2003a and 2003b). High-frequency terrain effects
are also evaluated in VOIGT and DENKER (2007). Helmert’s
methods of condensation are analyzed in HECK (2003) and
TSCHERNING and HECK (2005). Density variations are
estimated from gravity and elevation data in RÓZSA (2003),
while MLADEK (2006) discusses hydrostatic isostasy. An
evaluation of the global SRTM and GTOPO terrain data
sets in Germany is presented in DENKER (2005a). Problems
in connection with vertical reference frames are analyzed
in HECK (2004).
FLURY (2006) compared short wavelength spectral properties
of gravity anomalies from various regions and derived
a degree variance model for topographically reduced
gravity anomalies. FINN and GRAFAREND (2003) constructed
maps of ellipsoidal vertical deflections. Combined
regional gravity field solutions were studied in EICKER et
al. (2006), GITLEIN et al. (2005), KUROISHI and DENKER
(2003), ROLAND and DENKER (2005b) and WOLF and
KIELER (2007).
2. Observation Techniques
A digital transportable zenith camera system was developed
and tested at the Institut für Erdmessung (IfE), Leibniz
Universität Hannover (HIRT 2003 and 2004, HIRT et al.
2005B, HIRT and BÜRKI 2003 and 2006). Besides hardware
improvements (HIRT and KAHLMANN 2004, KAHLMANN
et al. 2004), refraction studies (HIRT 2006) and accuracy
Regional Gravity Field Modelling
H. DENKER 1
verifications (HIRT et al. 2004 and 2005a) were performed.
Furthermore, the system was used in several observation
campaigns in Switzerland (BÜRKI et al. 2005, HIRT and
REESE 2004, MARTI et al. 2004, MÜLLER et al. 2004a) and
Germany (HIRT et al. 2006 and 2007, FLURY et al. 2006).
The results indicate an observational accuracy of about 0.1"
for the astronomic positions.
3. Geophysical Investigations
A homogeneous Bouguer gravity map was published for
the Rhine Graben in cooperation between the Leibniz
Institute for Applied Geosciences (GGA-Institut),
Hannover, and the Institut de Physique du Globe de Strasbourg
(ROTSTEIN et al. 2006). Further regional data compilations
and interpretations were realized for the Alps
(ZANOLLA et al. 2006) and the Eifel region (RITTER et al.
2007). Local geophysical interpretations based on gravity
observations were presented for maar volcanic structures
in the Upper Lusatia region (GABRIEL 2003a, LINDNER et
al. 2006, SCHULZ et al. 2005), in Bavaria (GABRIEL 2003b),
for the UNESCO world heritage site Messel Pit (BUNESS
et al. 2004, JACOBY et al. 2005, SCHULZ et al. 2005), and
for a tuff chimney structure near Ebersbrunn, West-Saxony
(KRONER et al. 2006). Gravimetric and geodynamic
modelling was carried out in the Vogtland and NW-
Bohemia region to study swarm earth quake activities
(HOFMANN 2003, HOFMANN et al. 2003). A combined 3-D
interpretation of gravity and aeromagnetic data, continental
and marine seismic profiles, well logs and geological crosssections
was done for the northern Red Sea rift and Gulf
of Suez (SALEH et al. 2006). Another field of investigation
were Pleistocene valleys in northern Germany with
emphasis on ground water related structures (GABRIEL
2006, GABRIEL et al. 2003, RUMPEL et al. 2006, THOMSEN
and GABRIEL 2006, WIEDERHOLD et al. 2005).
Within the Collaborative Research Centre 526 “Rheology
of the Earth – from the Upper Crust to the Subduction
Zone” at the Ruhr-Universität Bochum, a study of the
Earth’s gravity field around Crete has given insight into the
density structure of the Hellenic subduction zone (CASTEN
and SNOPEK 2006, PRUTKIN and CASTEN 2007, SNOPEK and
CASTEN 2006, SNOPEK et al. 2007). Computer aided gravity
modelling was done by application of forward techniques
and by direct inversion; new software was developed within
the framework of the project.
Gravity data were archived in the Geophysical Information
System, maintained by the GGA-Institut (KÜHNE 2005 and
2006, KÜHNE et al. 2003). Actually, the Geophysical
1 Heiner Denker: Institut für Erdmessung, Leibniz Universität Hannover, Schneiderberg 50, D-30167 Hannover, Germany,
Fax: +49 - 511 - 7622796, Tel. +49 - 511 - 762-2796, e-mail: denker@ife.uni-hannover.de