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  • German  (4)
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  • 1
    Publication Date: 2017-06-10
    Description: Design and performance of waveguide mixers at 1.4 THz and 1.9 THz based on NbTiN phonon-cooled hot electron bolometers (HEB) fabricated on a 2 æm thick Si_3N_4 membrane. The membrane is bonded to a silicon frame in the mixer block using a flip chip process. Simulated RF coupling is compared with experimental results, showing good agreement. Receiver noise temperature measurements show uncorrected values of 1600 K at 1.4 THz and 2100 K at 1.9 THz, both at 1.5 GHz intermediate frequency. Device cooling on the membrane seems not to be problematic. The mixers are used in receivers for SOFIA (GREAT & CONDOR) and APEX (CONDOR).
    Description: thesis
    Keywords: TBG 000 ; Infrarot-Astronomie
    Language: German
    Type: monograph , publishedVersion
    Format: 153 S.
    Format: application/pdf
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  • 2
    Publication Date: 2020-02-12
    Description: Earth materials can be characterized by their electrical resistivity. Geophysicists use electromagnetic methods to decipher the electrical structure of earth, to determine chemical and physical properties of rocks and to investigate associated dynamic processes within earth. Measured data, typically observed at earth’s surface, cannot be directly converted into a comprehensive image of the subsurface. To achieve this goal geophysicists use mathematical and numerical techniques which require significant computational resources. We discuss application of electromagnetic sounding methods, show depth sections derived from 3D inversion, discuss field configuration simulations and resolution tests, introduce the concept and potential of joint inversion and give an outlook on monitoring to decipher temporal changes of the subsurface.
    Language: German
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 3
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    In:  System Erde
    Publication Date: 2020-02-12
    Description: Understanding the electrical conductivity of earth materials is important to decipher structures and processes in Earth’s deep interior. Electromagnetic deep sounding methods are used to unravel structures at depths from a few tens of meters to tens of kilometres. The Geo-Electromagnetic Group of GFZ is interested in all aspects of this research field: sensor and instrument development, novel algorithms for signal processing and data inversion, conductivity measurements on rock samples and application of the method to basic and applied research topics. We present examples from the San Andreas Fault, California, South Africa and the North German Basin.
    Language: German
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 4
    Publication Date: 2020-02-12
    Description: Neural networks are simplified mathematical models to simulate certain aspects of information processing in biological nervous systems. Some principles adopted from nature include parallel processing, learning by example, and abstraction of knowledge. Neuro-computing is a rapidly growing branch of research, where constantly new types of neural networks are developed for different applications. Pattern recognition and classification is the typical application of such approaches. Many tasks in geosciences, particularly in data interpretation, can be considered and treated as classification problems. In such a terminology, the studied objects (e.g. sub-regions of earth models) are classified as rock types based on characteristic features (e.g. physical properties). Numerical solutions have to address challenges such as incorrectness and incompleteness of data, and overlap in some properties for different lithologies. The self-organizing map is an intriguing concept, which allows to establish a certain classification behavior by unsupervised learning. We developed a work flow at GFZ, which includes preparation of data, application of learning rules, the segmentation of the trained map by adopting image processing techniques, and employment of knowledge. Applications are shown from geothermal exploration projects in the Northeast German basin and in Indonesia, where different geophysical models from the same study area were combined for a joint lithological interpretation.
    Language: German
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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