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

94
Mean sea level and sea level variations
The improvements in satellite altimetry in the last four years
provided excellent opportunities to study the mean sea
surface and its temporal variations. In this context interdisciplinary
aspects became more and more important. The
global sea level change as seen by altimetry, GNSS and tide
gauge measurements has been investigated in detail (BOSCH
2005). The different effects in sea level variability were
discussed by FENOGLIO-MARC and GROTEN (2003). The
relation between bottom pressure, vertical structure of the
ocean and sea level has also been studied (VINOGRADOVA
et al. 2007) A combination of altimetry and satellite gravity
allowed the estimation of the steric component in sea level
variations (LOMBARD et al. 2006).
Regional studies of sea level variations were carried out for
the North Atlantic (KUHN et al. 2005), the Mediterranean
(TSIMPLIS et al. 2005, FENOGLIO-MARC et al. 2006) and the
Baltic Sea (NOVOTNY et al. 2005).
Verification of mean sea level variations by
combination of techniques
The intercomparison of different observation techniques
and models is necessary in order to detect techniquedependent
errors and biases in a suitable procedure as well
as possible unmodeled effects. The range of investigations
covers ionospheric corrections in satellite altimetry
(BRUNINI et al. 2005), altimeter biases of different missions
as determined in the Mediterranean (FENOGLIO-MARC et
al. 2003) and the combination of observations and an
oceanographic model in the Baltic Sea (NOVOTNY et al.
2006).
The relation of sea level variations and vertical crustal
movements has been studied in detail in the Mediterranean
(FENOGLIO-MARC et al. 2004).
Polar Ice Sheets
The polar ice sheets are of cruicial importance as a major
component of sea level change and as an indicator for
climate change. Several regional studies were carried out
in order to investigate surface geometry, dynamics and mass
balance in specific areas.
In Antarctica, the ice shelves represent sensitive indicators
to climate changes. The Nivlisen, located in the Atlantic
sector of the Antarctic coast, was studied by combining
geodetic and glaciological observations (HORWATH et al.
2006). The tidal interaction of the Mertz glacier was
Sea Level and Ice Sheets
R. DIETRICH 1
investigated using remote sensing and in-situ observations
(LEGRESY et al. 2004).
Only recently discovered, the Antarctic subglacial lakes
attracted great attention as remarkable objects of joint international
research activities. For the largest one, the 250 km
long Lake Vostok in East Antarctica, the surface geometry
has been determined from radar altimeter data (RÖMER et
al. 2007). Furthermore, the glaciological flow regime
(WENDT et al. 2006) and tidal effects within the lake were
determined (WENDT 2005, WENDT et al. 2005).
In the Arctic, the large glaciers of the Greenland Ice Sheet
represent one main topic of research. The largest glacier
there, the Jakobshavn Isbrae, shows an acceleration of flow
velocity from 20 m/day in 1995 up to 45 m/day in 2004
with corresponding effects on sea level (MAAS et al. 2006,
DIETRICH et al. 2007).
The potential of GNSS reflections over ice sheets for
glaciological investigations has been compiled in a feasibility
study (WIEHL et al. 2003).
Geodetic Research in Arctic and Antarctic
Regions
The geodetic research in polar regions, which has been
intensified recently due to the International Polar Year
2007/2008, contributes also to the geodetic tasks in global
scale. This includes especially the reference frame and the
detection of horizontal crustal movements in Antarctica
(DIETRICH et al. 2004) as well as ice-induced vertical crustal
movements in Antarctica (SCHEINERT et al. 2005, 2006) and
Greenland (DIETRICH et al. 2005).
SASGEN et al. (2007a) determined constraints on the
present-day mass-balance and the ongoing glacial-isostatic
adjustment (GIA) in Antarctica using the GRACE
gravity-field time series. The approach involved noise
reduction in the GRACE gravity fields based on the
statistical analysis of the temporal variability of Stokes
potential coefficients (MARTINEC et al., 2007) and optimal
smoothing of the gravity field (SASGEN et al., 2006).
Additionally, a method for the evaluation and combination
of the GRACE gravity-field solutions based on an a priori
model was proposed (SASGEN et al., 2007b).
Predictions describing the prominent geoid changes arising
from present and past glacial changes in Antarctica
(SASGEN et al., 2005) and Greenland (FLEMING et al., 2004)
were made and, for Antarctica, adjusted to the noisereduced
GRACE observations. SASGEN et al. (2007a)
1 Reinhard Dietrich: Institut für Planetare Geodäsie, Techn.ische Universität Dresden, Mommsenstraße 13, D - 01062 Dresden. Germany,
Tel. +49 - 0351 - 463 346 52, Fax +49 - 351 - 463 370 63, e-mail dietrich@ipg.geo.tu-dresden.de