Archeological site investigations using very high resolution 3D seismics

In the IMAGO project, the problem of finding wooden shipwrecks buried in the fine-grained sediment bottoms of shallow Dutch inland waterways is addressed. A trial survey was carried out, using a Very High Resolution 3D seismic acquisition system, which consists of a single source and 8 streamers. With a suitable shot interval and a smart recording strategy we can obtain a subsurface spatial sampling grid of 0.5 by 0.5 m. To support this dense grid, accurate navigation data is obtained by two DGPS antennas enabling us to calculate the orientation of the streamers independent of the sailing direction. Normal move out velocity is not critical to the stacking process, but vertical position variations, together with horizontal (offset) variations can be detrimental. Aided by the multibeam echo sounder and by picking the water bottom reflection times from the seismic data, the image is greatly enhanced

River bed classification using multi-beam echo-sounder backscatter data

The Netherlands form the delta for some of the major river systems of Europe, comprising the Rhine, the Meuse, the Scheldt and the Eems. These rivers are valuable parts of national and international ecological networks and are of high economic importance. A minimum depth should be guaranteed to keep the rivers navigable. This depth depends not only on water discharge but also on river bed topography that changes dynamically in response to discharge fluctuations. Rijkswaterstaat is the Dutch governmental organization that is responsible to maintain the main river systems for both shipping, flood conveyance and ecological purposes. To keep the rivers navigable daily dredging activities are carried out. Furthermore the discharge capacity of the rivers is enlarged and the ecological quality is improved by widening the river and making secondary channels. The river topography and its dynamics are affected by spatial variations in bed sediment composition, thus making knowledge of the spatial sediment distribution highly important. It proved to be sufficient to detect a number of classes to produce classification maps of the bottom. An attractive system to be used for obtaining information on both the river bed bathymetry and sediment composition is the multi-beam echo-sounder (MBES). This sonar emits short pulses of sound towards the river bed to determine the depth and the backscatter strength for a large number of closely-spaced beams. The MBES provides high spatial coverage of an area at moderate costs and within short time. The backscatter strengths are known to be indicative for the sediment types, and consequently have potential with regard to sediment classification. Consequently, the MBES system appears as a good alternative to the conventional, expensive and time-consuming, approach of mapping the river bed composition by taking a large number of physical sediment samples. In the present paper, the results of a novel and fairly simple sediment classification method are presented. The method that developed in the Acoustic Remote Sensing Group of Delft University of technology is briefly described in the following section.Control & OperationsAerospace Engineerin

The underwater soundscape of the North Sea

As awareness on the impact of anthropogenic underwater noise on marine life grows, underwater noise measurement programs are needed to determine the current status of marine areas and monitor long-term trends. The Joint Monitoring Programme for Ambient Noise in the North Sea (JOMOPANS) collaborative project was funded by the EU Interreg to collect a unique dataset of underwater noise levels at 19 sites across the North Sea, spanning many different countries and covering the period from 2019 to 2020. The ambient noise from this dataset has been characterised and compared - setting a benchmark for future measurements in the North Sea area. By identifying clusters with similar sound characteristics in three broadband frequency bands (25–160 Hz, 0.2–1.6 kHz, and 2–10 kHz), geographical areas that are similarly affected by sound have been identified. The measured underwater sound levels show a persistent and spatially uniform correlation with wind speed at high frequencies (above 1 kHz) and a correlation with the distance from ships at mid and high frequencies (between 40 Hz and 4 kHz). Correlation with ocean current velocity at low frequencies (up to 200 Hz), which are susceptible to nonacoustic contamination by flow noise, was also evaluated. These correlations were evaluated and simplified linear scaling laws for wind and current speeds were derived. The presented dataset provides a baseline for underwater noise measurements in the North Sea and shows that spatial variability of the dominant sound sources must be considered to predict the impact of noise reduction measures.publishedVersio