Bathymetry and Geodesy Group

Multibeam bathymetric survey techniques provide a rapid means of determining the morphology and nature of the seafloor. The recent Hydrosweep DS-2 System onboard R/V Polarstern provides 59 individual soundings of the water depth and echo strength for each ping. Moreover sidescan information (2048 echos per ping) is retrieved. The system can be operated with 90 or 120 degrees fan angle and is designed for deep sea observations.

Hydrosweep multibeam bathymetry is a paramount "first step" reconnaissance tool used by AWI scientists for multifarious marine surveys. Multibeam bathymetry, backscatter intensity and sidescan data are collected as the first stage of multiparameter geophysical, geological, and biological surveys. The multibeam bathymetric data are used to create Digital Terrain Models (DTMs) of the seafloor. These are used to interpret features such as channels, areas of bedrock outcrop, small scale bedforms, rocks and other small objects. Acoustic backscatter intensity measurements are used to determine physical properties like the distribution of coarse and fine sediments. The DTMs and sidescan images provided by the multibeam system build the basis for the preliminary interpretation of seafloor processes and features, and are used to plan subsequent studys such as seismic surveys, seafloor sampling, or ROV operations.

The role of surveying and geodesy in classical polar research expeditions has mainly been restricted to determine positions and to provide frames for mapping. But the field of application has been expanding dramatically in the last decades. New satellite techniques with increasing accuracies, especially the Global Positioning System (GPS) and satellite altimetry, provide excellent weather independent and highly accurate tools for the operation under harsh conditions in polar regions.

Geodetic methods, such as GPS and tide gauge measurements, can be used to determine both relative and absolute rates of tectonic plate movements. A global network of IGS sites provides a geodetic datum in the IERS Terrestrial Reference Frame (ITRF). These precisely known IGS stations are available as reference for local measurements.

Long term observations of the sea surface with tide gauge measurements are used to detect variations in the mean sea level (MSL). By linking the tide gauge benchmarks to ITRF-referenced GPS markers, a vertical datum can be derived for the local site. This allows a separation of sea level changes from plate uplift, which might result either from geodynamic processes or possibly from climate changes, e.g. melting of polar ice masses. Thus geodetic techniques contribute not only to geophysics, but also to global climate research.

Gravity measurements on land, as well as at sea, are needed for the derivation of the gravity field, which provides a fundamental basis for the understanding of tectonic processes. Gravity anomalies, additionally computed from satellite altimetry, reveal plate boundaries, fracture zones and bathymetric structures. Together with tide gauge records gravity data provide information about the vertical datum. This also is important to reduce ellipsoid-based GPS data to orthometrical heights.