Germany: GAF has developed a new innovative approach for deriving bathymetry from space by simultaneously using differential spectral attenuation and stereo-information from satellite imagery for hydrocarbon exploration and for the performance of seismic surveys. Bathymetry is the underwater topography of lakes or ocean floors and constitutes an important information layer on hydrographic charts.
Traditional ways of acquiring bathymetry data include the carrying out of depth measurements using sounding lines, sonar or LiDAR. However, as ship-based or airborne measurements take time to prepare and perform and can only cover fairly small geographic areas in a single pass, quite significant expenditure is usually required in terms of time and money.
Bathymetric information is of importance in offshore hydrocarbon exploration: knowledge of the seabed morphology and of subtle submarine features, such as so-called mud volcanoes, can provide valuable indicators to prospectors. Furthermore, accurate sea-bottom morphology facilitates the correct interpretation of 3D seismic surveys.
The method was recently used to successfully map a large area in the Caspian Sea for RWE Dea Azerbaijan, an international oil and gas company headquartered in Hamburg, Germany. The results provided valuable information suitable for hydrocarbon exploration and for the performance of seismic surveys. For the project, GAF made use of satellite remote and its new stereo approach for this task and mapped an area of 230 sqkm.
The bathymetric analysis was based on a stereo pair of very high resolution multispectral satellite images. First, stereoscopic measurements were performed, which provided depth information about clearly recognisable submerged features and topography. In a second step, a bathymetric model was created using these features and the satellite imagery, in order to provide area-wide bathymetric mapping of depths and seabed morphology.
The bathymetric information was collected in a regular grid with a spatial resolution of 4m and had an absolute vertical accuracy better than 2m. The modelling approach utilises the spectral absorption of light in the water column, which is dependent on the water depth. The method is based on the amount of light penetration into the water column, which under favourable circumstances can reach depths of up to 20m.
Commenting on the technology, Dr. Christian Bücker, Manager of Research and Development at RWE Dea, stated, "The satellite-derived bathymetry provides valuable information for our area of interest in the Caspian sea. The bathymetric analysis was performed successfully and has sufficient accuracy to detect and map mud volcanoes. The existing sparse bathymetry knowledge of the areas has thus been greatly improved."