13 research outputs found
Indications of marine benthos occurrence from multi-spectral multi-beam backscatter data: a case study in the North Sea
No full textTo facilitate the conservation of seafloor habitats and planning of offshore activities, there is a growing need for mapping marine benthos in an effective and efficient way. Acoustic data acquired by multi-beam echosounders (MBES) have been extensively used for large-scale and high-resolution seafloor characterization. A deeper understanding of the relationship between backscatter data and sediment compositions can help to identify the benthos occurrence from the MBES data. With two multi-spectral MBES datasets collected near the western Wadden Sea islands in the North Sea, we investigated the potential of mapping marine benthos through backscatter classification. Two unsupervised classification methods, i.e., Bayesian classification, which mainly exploits the backscatter strength from incident angles larger than 20°, and hierarchical clustering of the backscatter strength at different angular ranges, were employed and the results were compared. The classification results from both methods showed a good correspondence with sediment properties such as the median grain size. Moreover, based on a principal component analysis of bottom sample properties, the hierarchical clustering results indicated a better distinction between contributions from the gravel content and benthos occurrence, e.g., sand mason worm density, than Bayesian classification, through involving the backscatter angular variations. Classification for multiple frequencies, on the other hand, showed little difference regarding the relationship with bottom sample properties. Although the backscatter difference between frequencies was also found to positively correlate with certain sample properties, using multi-spectral features for acoustic classification in this study did not reveal additional information compared to single-frequency classification results
Characterizing seabed sediments using multi-spectral backscatter data in the North Sea
No full textAcoustic classification using single-beam and multi-beam echosounders has been widely applied in characterizing seabed sediments. Although previous studies have shown a better discrimination of fine and coarse sediments using multi-spectral echosounder data, analysis regarding comprehensive seabed sediment properties is still needed. In this study, we used single-beam data of 24 kHz, as well as multi-beam data of 90 and 300 kHz to investigate the benefits of multi-spectral backscatter data in describing sediment properties including median grain size; weight percentages of gravel, sand, and mud; volume percentages of stones, shell fragments, and living bivalves; as well as density of acoustically hard animals (molluscs and the tube-building worm Lanice conchilega). We classified data of each frequency in an unsupervised manner, using K-means clustering for the single-beam echo time series and Bayesian classification for the multi-beam backscatter. Compared with the top-layer sediment properties, we found classification of 90 and 300 kHz consistent with variations of median grain size and L. conchilega density, whereas classification of 24 kHz can also be related to the percentages of shell fragments and stones. In addition, one acoustic class of 24 kHz might indicate a higher gravel content in the subsurface of the study area. Although quantitative relationships between backscatter and sediment properties are still difficult to achieve given a limited number of samples, using multi-spectral backscatter data is a potential approach to characterize seabed sediments from various perspectives.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aircraft Noise and Climate EffectsControl & OperationsOptical and Laser Remote Sensin
The Environment & Planning vision: Enrichment in governmental participation
No full textA master thesis that addresses the 'to be developed' Environment & Planning vision and the possible support of this vision to the energetic society.Built Environment and Spatial Planning (B&S)Built Environment and Spatial Planning (B&S)Technology, Policy and Managemen
Solution of the vector wave equation using a Krylov solver with an algebraic multigrid approximated preconditioner
No full textElectrical Engineering, Mathematics and Computer Scienc
Optimization of a District Heating Network with the focus on heat loss
No full textIn the Netherlands most houses and buildings are connected to a gas network since the nineteen seventies to heat our houses and cook. In march of this year the new Dutch government announced that to meet the climate accord of Paris all dutch household should be of the gas net in 2030. To do this multiple alternatives to heat homes are available and one of those which has proven to be feasible over the last years is district heat. In a district heating network hot water is pumped round a city through a network of pipe lines to houses and other buildings. The network is split into a primary and a secondary network. In the primary network the heat is transported from the source, and in the secondary network the heat is pumped from a substation to the customers. The heat usually is rest heat of a STEG- or waste incineration power plant. With the increasing demand for heat due to the disconnection of the gas network, and at the same time the search for a more sustainable heat source for the district heating network like geothermal heat the prices and costs rise rapidly. This makes the heat loss in the system a more important issue also from a financial perspective. The current installed networks are all series 1 single pipe lines of ST/PUR/PE, this means the inner pipe through which the water flows is steal, followed by an insulating PUR layer which is covered by a protective PE layer. To decrease the heat loss from the pipe lines Nuon is looking at two possible options. Series 2 single piping which has a thicker insulating PUR layer and second the twin pipeline where both the steal supply and return lines areembedded into one insulating PUR layer and a protective PE shell. The heat loss calculations for the buried pipelines in the ground are done using empirical formulas found in literature. These are checked numerical using a pde-solver. Comparing both results it was the concluded the empirical formulas give a good approximation of the heat loss. It also showed the heat loss is for a great deal depended on the temperature in the pipe and the ground temperature. In current heat loss calculations done by Nuon the temperature gradient of the water entering the network and leaving the network in not taken into consideration. By using the ambient temperature and a formula formulated in literature an estimation of the ground temperature at the buried depth of the pipelines can be made. By dividing the network into a number of pieces with length 푑푥 and an individual temperature 푇 the temperature gradient overthe entire network is taken into account. Collected data by Nuon concerning the user demand and the ambient temperature makes it possible to simulate what is the mass flow through the system at any given time and to analyze how the system responds to a demand fluctuation. By analyzing what happens in the networks in term of heat loss during a diurnal heat curve the results show that the heat loss stays nearly constant during a day. There are however big differences between different days in different times of the year. Analyzing what happens over the course of a year especially in the summer during times of very low demand the system under performs. A main reason for this is caused by theminimum required temperature of 70 degrees Celsius at the customers due to salmonella regulations. This causes a lot of extra mass flow of hot water pumped around the system which heats up the return flow. This is also clearly notable from the efficiency of the network which drops tremendously in the summer. Comparing the difference in heat loss for the series 1, series 2 and twin system the results where as expected an decrease in the amount of heat lost, by 14.6% for series 2 and 39.70% for twin compared to series 1. The overall image of what happens actually stays the same with high return temperature and relative high heat loss and low efficiency in summer. There are a few options to further improve the performance of the system with a few percent by changing the inlet temperature or the location of the bypass valve. Financially speaking the twin system is also the better choice of the three. Compared to series 1 for series 2 the investment costs will increase because the materialsand instalment costs will increase. For the twin system the prices of the materials will increase and the placements of the welds will become more expansive however only half the number of pipe lines and joints is needed, so in total the prices will stay nearly the same compared to series 1. There is a lot of discussion on whether or not the maintenance costs will increase for the twin system, arguments for both cases are given. However the maintenance costs are so small compared to the costs of the heat loss that in every case the twin system is clearly the better choice.Mechanical Engineerin
Collaborate to accelerate: Exploring the empirical perspective on accelerating the initiation phase of inner-city redevelopment projects: from Industrial to mixed work-residential areas
No full textThe Dutch housing market is currently dealing with a significant dwelling deficit, which results in the need to accelerate the development of large quantities of dwellings in the urban areas. This thesis studies the redevelopment of inner-city industrial sites into mixed work-residential areas, especially focussing on the collaboration process between the municipality, landowner-users and project developers in the initiation phase. A Q-methodology research is conducted to identify which empirical perspectives exist on which factors are important when accelerating the collaboration process. Twenty-eight respondents from municipalities, landowner-users and project developers from three Dutch redevelopment projects have been used for this research. The main research findings are:- The identification of four distinctive empirical perspectives on which organisational, process and instrument factors need to be incorporated into the collaboration process to accelerate it. - The insight into the determinants that show which type of parties have which perspective and in which type of cases which perspectives are likely to occur.- Practical recommendations to design the collaboration process in a way that its acceleration potential is enlarged.- The assembly of the building block approach conceptual model that uses the insights in the perspectives and the determinants to construct a case specific collaboration approach. By designing the collaboration process according to the preferences of the involved parties, expressed by the four perspectives, the parties are more committed to the process which results in a more effective and therefore faster initiation phase. Eventually this can help to accelerate the construction of the needed dwellings. So, you have to collaborate to accelerate.Civil Engineering | Construction Management and Engineerin
Conservation implications of <i>Sabellaria spinulosa</i> reef patches in a dynamic sandy-bottom environment
No full textBiogenic reefs form biodiversity hotspots and are key components of marine ecosystems, making them priority habitats for nature conservation. However, the conservation status of biogenic reefs generally depends on their size and stability. Dynamic, patchy reefs may therefore be excluded from protection. Here, we studied epibenthos and epifauna density, richness, and community composition of patchy, dynamic Sabellaria spinulosa (ross worm) reefs in the North Sea. This study was conducted by comparing boxcore (endobenthos) and video transect (epifauna) data from two research campaigns in 2017 and 2019 to the Brown Bank area on the Dutch Continental Shelf, where S. spinulosa reefs were first discovered in 2017. The Brown Bank area is characterized by dynamic, migratory bedforms at multiple scales which potentially affect biogenic reef stability. We showed that S. spinulosa habitats had a patchy distribution and alternated with habitats comprised of plain sand. Average S. spinulosa habitat patch size was 5.57 ± 0.99 m and 3.94 ± 0.22 m in 2017 and 2019 respectively (mean ± SE), which especially in 2019 closely resembled the small-scale megaripple bedforms. Contrary to the endobenthos communities that were unaffected by S. spinulosa, epifauna density and species richness were at least two times higher in S. spinulosa habitats compared to sandy habitats, resulting in different community compositions between the two habitat types. We showed that S. spinulosa persisted in the area for almost 2 years. Although the stability of individual patches remained unclear, we demonstrated that even patchy biogenic reefs may promote density and local biodiversity of mobile, epibenthic species, very likely as a result of increased habitat heterogeneity provided by reef habitat patches. This indicates that patchy biogenic reefs that occur in dynamic environments may also have high ecological value and their conservation status should be (re)considered to ensure their protection
Measuring centimeter-scale sand ripples using multibeam echosounder backscatter data from the Brown Bank area of the Dutch continental shelf
No full textBackscatter data from multibeam echosounders are commonly used to classify seafloor sediment composition. Previously, it was found that the survey azimuth affects backscatter when small organized seafloor structures, such as sand ripples, are present. These sand ripples are too small to be detected in the multibeam bathymetry. Here, we show that such azimuth effects are time dependent and are useful to examine the orientation of sand ripples in relation to the flow direction of the tide. To this end, multibeam echosounder data at four different frequencies were gathered from the area of the Brown Bank in the North Sea. The acoustic results were compared to video and tide-flow data for validation. The sand ripples affected the backscatter at all frequencies, but for the lowest frequencies the effect was spread over more beam angles. Using the acoustic data made it possible to deduce the orientations of the sand ripples over areas of multiple square kilometers. We found that the top centimeter(s) of the seafloor undergoes a complete transformation every six hours, as the orientation of the sand ripples changes with the changing tide. Our methodology allows for morphology change detection at larger scales and higher resolutions than previously achieved
Linking the morphology and ecology of subtidal soft-bottom marine benthic habitats: A novel multiscale approach
No full textHigh-resolution surveying techniques of subtidal soft-bottom seafloor habitats show higher small-scale variation in topography and sediment type than previously thought, but the ecological relevance of this variation remains unclear. In addition, high-resolution surveys of benthic fauna show a large spatial variability in community composition, but this has yet poorly been linked to seafloor morphology and sediment composition. For instance, on soft-bottom coastal shelves, hydrodynamic forces from winds and tidal currents can cause nested multiscale morphological features ranging from metre-scale (mega)ripples, to sand waves and kilometre-scale linear sandbanks. This multiscale habitat heterogeneity is generally disregarded in the ecological assessments of benthic habitats. We therefore developed and tested a novel multiscale assessment toolbox that combines standard bathymetry, multibeam backscatter classification, video surveying of epibenthos and box core samples of sediment and macrobenthos. In a study on the Brown Bank, a sandbank in the southern North Sea, we found that these methods are greatly complementary and allow for more detail in the interpretation of benthic surveys. Acoustic and video data characterised the seafloor surface and subsurface, and macrobenthos communities were found to be structured by both sandbank and sand wave topography. We found indications that acoustic techniques can be used to determine the location of epibenthic reefs. The multiscale assessment toolbox furthermore allows formulating recommendations for conservation management related to the impact of sea floor disturbances through dredging and trawling.Aircraft Noise and Climate EffectsHydraulic EngineeringEnvironmental Fluid Mechanic
Beyond connecting the dots: A multi-scale, multi-resolution approach to marine habitat mapping
No full textConflicts of interests between economic and nature conservation stakeholders are increasingly common in coastal seas, inducing a growing need for evidence-based marine spatial planning. This requires accurate, high-resolution habitat maps showing the spatial distribution of benthic assemblages and enabling intersections of habitats and anthropogenic activities. However, such detailed maps are often not available because relevant biological data are scarce or poorly integrated. Instead, physiotope maps, solely based on abiotic variables, are now often used in marine spatial planning. Here, we investigated how pointwise, relatively sparse biological data can be integrated with gridded, high-resolution environmental data into informative habitat maps, using the intensively used southern North Sea as a case-study. We first conducted hierarchical clustering to identify discrete biological assemblages for three faunal groups: demersal fish, epifauna, and endobenthos. Using Random Forest models with high-resolution abiotic predictors, we then interpolated the distribution of these assemblages to high resolution grids. Finally, we quantified different anthropogenic pressures for each habitat. Habitat maps comprised a different number of habitats between faunal groups (6, 13, and 10 for demersal fish, epifauna, and endobenthos respectively) but showed similar spatial patterns for each group. Several of these ‘fauna-inclusive’ habitats resembled physiotopes, but substantial differences were also observed, especially when few (6; demersal fish) or most (13; epifauna) physiotopes were delineated. Demersal fishing and offshore wind farms (OWFs) were clearly associated with specific habitats, resulting in unequal anthropogenic pressure between different habitats. Natura-2000 areas were not specifically associated with demersal fishing, but OWFs were situated mostly inside these protected areas. We thus conclude that habitat maps derived from biological datasets that cover relevant faunal groups should be included more in ecology-inclusive marine spatial planning, instead of only using physiotope maps based on abiotic variables. This allows better balancing of nature conservation and socio-economic interests in continental shelf seas.</p
