Dr. Christopher T. F. Kuehl Profile

Dr. Christopher T. F. Kuehl

System Engineer & Project Manager

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Publications (5)

Proceedings Article | 12 July 2023 Open Access

MERLIN high energy laser source for methane sensing at 1645 nm

Sven Hahn, Bastian Gronloh, Christian Wührer, Dimitrios Kokkinos, Christopher Kühl, Jana Ammersbach, Marie Livrozet, Hans-Dieter Hoffmann, Peter Bartsch

Proceedings Volume 12777, 127770M (2023) https://doi.org/10.1117/12.2688829

KEYWORDS: Optical parametric oscillators, Design and modelling, Laser applications, Thermal stability, Oscillators, Laser stabilization, Crystals, Methane, Ferroelectric materials, Astronomical imaging

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Proceedings Article | 12 July 2023 Open Access

MERLIN (MEthane Remote sensing LIdar missioN): heading towards PFM and observation of interesting effects

N. Strasser, C. Wührer, C. Kühl, M. Haiml, D. Viehmann, M. Kritzler

Proceedings Volume 12777, 127772T (2023) https://doi.org/10.1117/12.2690303

KEYWORDS: Avalanche photodetectors, Equipment, Fabry–Perot interferometers, Quantum efficiency, Methane, LIDAR, Design and modelling, Astronomical imaging, Frequency modulation, Fermium

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The Methane Remote Sensing LIDAR Mission (MERLIN) is a joint French-German cooperation on the development, launch and operation of a climate monitoring satellite, executed by the French Space Agency CNES and the German Space Agency DLR. It is focused on global measurements of the spatial and temporal gradients of atmospheric Methane (CH4) with a precision and accuracy sufficient to determine Methane fluxes significantly better than with the current observation network. Merlin is a LIDAR Instrument using the Integrated Path Differential Absorption (IPDA) principle. This instrument principle relies on the different absorption of the laser signal by atmospheric Methane at two laser wavelengths – online and offline – both around 1645 nm, reflected by the Earth surface. The attenuation is strong at the online wavelength; the offline “reference” wavelength is selected to be only marginally affected by Methane absorption. Being an active instrument with its own light source, the MERLIN LIDAR Instrument does not rely on sun illumination of the observed areas and therefore operates continuously over the orbit. Airbus DS GmbH was selected by DLR as the industrial Prime Contractor for the Mission Phase C/D to build the MERLIN Payload, which is the first realization of an IPDA LIDAR for space in Europe. This presentation will concentrate on the Architecture and the Design of the MERLIN Payload, which passed the CDR in 2020 and is now progressing in Phase D. Further details of the instrument development status will be shown by an overview of the current hardware and design status of the major subsystems. A spotlight of this paper will be a finding when performing a low-bandwidth spectral characterization of an Avalanche Photo Diode (APD), which revealed features which were not expected: Next to the known global spatial and spectral variations, the scans have shown an unexpected narrowband spectral dependence, as well as a spatial dependence, which was a factor of two worse than originally expected. Further tests also showed a thermal dependence of the QE related to the APD operating temperature, which strongly exceeded the expected variations. These unexpected effects would have led to a highly increased Radiometric Systematic Error (RSE) in the Differential Absorption Optical Depth (DAOD). The root-cause was identified as an Etalon effect caused by the APD substrate, which in addition varied over the APD due to slight changes in the layer thickness. The effect is strongly field angle dependent, which made a review of the scan setup necessary. Therefore, the setup was adapted via a stepwise increase of the field angle, which reduced the Etalon effect. Consequentially, the Etalon effect as root cause for these observations has been confirmed by experiments, as well as theoretical analysis, which was shown to be in line with the measurement results.

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Proceedings Article | 12 July 2019 Open Access

MERLIN: overview of the design status of the lidar Instrument

Christian Wührer, Christopher Kühl, Stefano Lucarelli, M. Bode

Proceedings Volume 11180, 1118028 (2019) https://doi.org/10.1117/12.2535999

KEYWORDS: LIDAR, Mirrors, Methane, Absorption, Optical benches, Pulsed laser operation, Optical parametric oscillators, Interfaces, Telescopes, Sensors

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Proceedings Article | 8 November 2012 Paper

Fast Fourier Transform Co-processor (FFTC), towards embedded GFLOPs

Christopher Kuehl, Uwe Liebstueckel, Isaac Tejerina, Michael Uemminghaus, Felix Witte, Michael Kolb, Martin Suess, Roland Weigand, Nicholas Kopp

Proceedings Volume 8539, 853905 (2012) https://doi.org/10.1117/12.974825

KEYWORDS: Field programmable gate arrays, Digital signal processing, Fourier transforms, Control systems, Human-machine interfaces, Prototyping, Synthetic aperture radar, Computer programming, Data storage, Clocks

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Proceedings Article | 6 August 2010 Paper

NIP: the near infrared imaging photometer for Euclid

Mario Schweitzer, Ralf Bender, Reinhard Katterloher, Frank Eisenhauer, Reiner Hofmann, Roberto Saglia, Rory Holmes, Oliver Krause, Hans-Walter Rix, Jeff Booth, Parker Fagrelius, Jason Rhodes, Suresh Seshadri, Alexandre Refregier, Jerome Amiaux, Jean-Louis Augueres, Olivier Boulade, Christophe Cara, Adam Amara, Simon Lilly, Eli Atad-Ettedgui, Anna-Maria Di Giorgio, Ludovic Duvet, Christopher Kuehl, Mohsin Syed

Proceedings Volume 7731, 77311K (2010) https://doi.org/10.1117/12.857031

KEYWORDS: Sensors, Near infrared, Staring arrays, Electronics, Monochromatic aberrations, Photometry, Point spread functions, Thermography, Galactic astronomy, Interfaces

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