Prof. Johannes Kiefer Profile

Prof. Johannes Kiefer

at Univ Bremen

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Proceedings Article | 22 September 2015 Paper

Shearlet-based edge detection: flame fronts and tidal flats

Emily King, Rafael Reisenhofer, Johannes Kiefer, Wang-Q Lim, Zhen Li, Georg Heygster

Proceedings Volume 9599, 959905 (2015) https://doi.org/10.1117/12.2188652

KEYWORDS: Edge detection, Wavelets, Synthetic aperture radar, Flame detectors, Image processing, Detection and tracking algorithms, Environmental sensing, Image segmentation, Visualization, Mathematics

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Shearlets are wavelet-like systems which are better suited for handling geometric features in multi-dimensional data than traditional wavelets. A novel method for edge and line detection which is in the spirit of phase congruency but is based on a complex shearlet transform will be presented. This approach to detection yields an approximate tangent direction of detected discontinuities as a byproduct of the computation, which then yields local curvature estimates.

Two applications of the edge detection method will be discussed. First, the tracking and classification of flame fronts is a critical component of research in technical thermodynamics. Quite often, the flame fronts are transient or weak and the images are noisy. The standard methods used in the field for the detection of flame fronts do not handle such data well. Fortunately, using the shearlet-based edge measure yields good results as well as an accurate approximation of local curvature. Furthermore, a modification of the method will yield line detection, which is important for certain imaging modalities.

Second, the Wadden tidal flats are a biodiverse region along the North Sea coast. One approach to surveying the delicate region and tracking the topographical changes is to use pre-existing Synthetic Aperture Radar (SAR) images. Unfortunately, SAR data suffers from multiplicative noise as well as sensitivity to environmental factors. The first large-scale mapping project of that type showed good results but only with a tremendous amount of manual interaction because there are many edges in the data which are not boundaries of the tidal flats but are edges of features like fields or islands. Preliminary results will be presented.

Proceedings Article | 16 September 2014 Paper

Studying biofuel aerosol evaporation rates with single particle manipulation

S. Corsetti, R. Miles, J. Reid, J. Kiefer, D. McGloin

Proceedings Volume 9164, 91642W (2014) https://doi.org/10.1117/12.2061378

KEYWORDS: Bioalcohols, Aerosols, Optical tweezers, Atmospheric particles, Electrodynamics, Biofuels, Light scattering, Climate change, Combustion, Video

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The significant increase in the air pollution, and the impact on climate change due to the burning of fossil fuel has led to the research of alternative energies. Bio-ethanol obtained from a variety of feedstocks can provide a feasible solution. Mixing bio-ethanol with gasoline leads to a reduction in CO emission and in NOx emissions compared with the use of gasoline alone. However, adding ethanol leads to a change in the fuel evaporation. Here we present a preliminary investigation of evaporation times of single ethanol-gasoline droplets. In particular, we investigated the different evaporation rate of the droplets depending on the variation in the percentage of ethanol inside them. Two different techniques have been used to trap the droplets. One makes use of a 532nm optical tweezers set up, the other of an electrodynamics balance (EDB). The droplets decreasing size was measured using video analysis and elastic light scattering respectively. In the first case measurements were conducted at 293.15 K and ambient humidity. In the second case at 280.5 K and a controlled environment has been preserved by flowing nitrogen into the chamber. Binary phase droplets with a higher percentage of ethanol resulted in longer droplet lifetimes. Our work also highlights the advantages and disadvantages of each technique for such studies. In particular it is challenging to trap droplets with low ethanol content (such as pure gasoline) by the use of EDB. Conversely such droplets are trivial to trap using optical tweezers.

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