Dr. Corneli Keim Profile

Dr. Corneli Keim

at Airbus Defence and Space

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Publications (7)

Proceedings Article | 20 September 2020 Presentation + Paper

The infrared Fourier transform spectrometer and the infrared imager instrument concepts for the FORUM mission, ESA's 9th Earth Explorer

Charlotte Pachot, Bernardo Carnicero Dominguez, Hilke Oetjen, Bernd Sierk, Flavio Mariani, Stefanie Riel, Gonçalo Rodrigues, Miguel Copano, Asier Martínez Carou, Luca Palchetti, Magdalena Lippa, Philippe Giaccari, Carmine Mastrandrea, Gaetan Perron, Corneli Keim, Manfred-Georg Kolm

Proceedings Volume 11530, 115300D (2020) https://doi.org/10.1117/12.2570867

KEYWORDS: Infrared spectroscopy, Infrared imaging, Infrared radiation, Spectroscopy, Fourier transforms, Imaging systems, Far infrared, Climatology, Environmental sensing, Space operations

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Proceedings Article | 12 July 2019 Open Access

Integration ghosts in interferograms: origin and correction

D. Lamarre, C. Keim, T. Guggenmoser

Proceedings Volume 11180, 1118063 (2019) https://doi.org/10.1117/12.2536138

KEYWORDS: Fourier transforms, Modulation, Convolution, Sensors, Spectrometers, Signal detection, Integration, Calibration, Mirrors, Phase shift keying

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Proceedings Article | 25 September 2018 Paper

A novel measurement approach to quantify diffuser induced Spectral Features

Florian Richter, Jasper Krauser, Corneli Keim, Dennis Weise, Mark Wenig

Proceedings Volume 10785, 107851Y (2018) https://doi.org/10.1117/12.2501943

KEYWORDS: Diffusers, Sensors, Spectrometers, Speckle pattern, Calibration, Telescopes, Light scattering, Speckle, Signal to noise ratio, Radiometry

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Spectrometers for Earth Observation require inflight radiometric calibration, for which the sun can be used as a known reference. For wide field instruments, a diffuser is placed in front of the spectrometer, scattering incoming sun light into the entrance slit and ensuring a homogenous illumination. As drawback, the diffuser induces a specific radiometric error caused by interference, which is called Spectral Features. The scattering of the incident light at the diffuser induces a random path difference yielding a specific interference pattern at the entrance slit, known as speckle pattern. These speckles are propagated through the disperser to the detector plane and further integrated by the detector pixels. The resulting feature can yield a significant signal error contribution, whose spectral variation is referred to as spectral features. The magnitude of this error is evaluated in terms of the Spectral Features Amplitude (SFA), the ratio of the signal standard deviation with its mean value over a specific wavelength range. There have been several ways implemented to measure the SFA of a spectrometer, e.g. end-to-end measurements with representative instruments. Typically the measurement accuracy is not sufficient to isolate the SFA from other radiometric errors. As a consequence, the instrument layout can hardly be optimized to suppress Spectral Features. We propose a novel characterization technique for Spectral Features based on the direct acquisition of monochromatic speckle patterns at the entrance slit. This allows the observation of Spectral Features below the level of the spectrometer spectral and spatial resolution. The Spectral Features are derived from various observed speckle patterns by properly mimicking the real spectrometer in the data analysis. With this measurement technique we are able to gain insight into the mechanism behind speckle induced Spectral Features. This insight will be used to develop a parameterized model facilitating the design of future space based spectrometers.

Proceedings Article | 29 September 2017 Presentation + Paper

Sentinel-5/UVNS instrument: the principle ability of a slit homogenizer to reduce scene contrast for earth observation spectrometer

Ch. Meister, C. Keim, J. Irizar, M. Bauer

Proceedings Volume 10423, 104231E (2017) https://doi.org/10.1117/12.2278619

KEYWORDS: Spectroscopy, Diffraction, Knowledge management, Calibration, Telescopes, Mirrors, Reflection, Wavefronts, Earth's atmosphere, Atmospheric particles

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Proceedings Article | 29 September 2017 Paper

Sentinel-5 instrument: status of design, performance, and development

T. Gühne, C. Keim, P. Bartsch, S. Weiß, M. Melf, W. Seefelder

Proceedings Volume 10423, 1042309 (2017) https://doi.org/10.1117/12.2278564

KEYWORDS: Spectrometers, Calibration, Short wave infrared radiation, Sensors, Space telescopes, Satellites

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Proceedings Article | 25 September 2017 Open Access

Sentinel-5: a novel measurement approach to quantify diffuser induced spectral features

Tristan Burns, Luis Ferreira, Corneli Keim, Lucia Perez Prieto, Jasper Simon Krauser, Dennis Weise

Proceedings Volume 10562, 105621L (2017) https://doi.org/10.1117/12.2296079

KEYWORDS: Diffusers, Spectroscopy, Speckle, Speckle pattern, Sensors, Astronomical imaging, Spectral resolution, Near infrared, Short wave infrared radiation, Visualization

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Many current and future earth observation satellites include spectrometer instruments, due to their suitability for identifying atmospheric gases through spectral signatures. Space based spectrometer instruments, such as the Sentinel-5-UVNS instrument (S5)[1] for the polar-orbiting MetOp Second Generation satellite, require appropriate calibration to incident sunlight in order to provide radiometrically accurate data. To ensure homogenous illumination of the entrance slit of the spectrometer during sunlight calibration, a diffuser is used to scatter the incoming light [1]. One contribution to inaccuracy in sunlight calibration is spectral features, an interference phenomenon resulting from scattering off the calibration unit diffuser [2].

The scattering of the incident light at the diffuser induces path differences, which yield a speckle pattern in the entrance slit. These speckles are still present at the focal plane of modern spectrometers through a combination of the high spectral and spatial resolution [2] [3]. Spectral features originate from the spectral integration of speckles in the slit to the spectrometer detector plane and further integration by the detector pixels [1]. The spectral variation following pixel integration is known as spectral features. The magnitude of this error is evaluated in terms of the Spectral Features Amplitude (SFA), the ratio of the signal standard deviation with its mean value, within a specific wavelength range [4].

This work proposes a novel measurement technique. This method is based on the acquisition of monochromatic speckle patterns in the slit over a finely sampled wavelength range. The net spectral features at the spectrometer detector are evaluated through post processing, by integrating acquired speckle patterns along the spectral resolution, and detector pixels. A key advantage of the proposed technique is the fine sampling and observation of the interference structures that make up spectral features, below the level of a spectrometer pixel. The simplified optical system and simulation of an idealised spectrometer reduces the error contributions when compared to measurement using an entire spectrometer.

The goal of this investigation is the measurement of the S5 spectral features amplitude associated with the Heraeus Optical Diffuser (HOD), a volume diffuser, and the TNO quasi volume diffuser (QVD), in conjunction with qualitative insight into the mechanism behind speckle induced spectral features, supporting the design of future spectrometers.

This paper is structured as follows: Section II details the system designed to acquire monochromatic speckle patterns. The monochromatic speckle patterns are obtained using a tuneable laser capable of wavelength steps below the speckle decorrelation wavelength, as investigated in III. Section IV outlines how monochromatic speckles are integrated to spectral features, and reports the SFA values for the HOD and QVD. The spectral features results are discussed in light of this inference in Section V, with conclusions presented in Section VI.

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Proceedings Article | 25 September 2017 Open Access

Sentinel-5: monitoring and correction of charge transfer inefficiency using the instrument spectral response function of the spectrometer

C. Keim, T. Gühne

Proceedings Volume 10562, 105624G (2017) https://doi.org/10.1117/12.2296046

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