Reducing the effect of integrating sphere speckle when characterizing the instrument line shape of a Fourier-transform hyperspectral imager

The stringent requirements for energy reference measurement represent a challenging task for integrated path differential absorption lidars to measure greenhouse gas columns from satellite or aircraft. The coherence of the lidar transmitter gives rise to speckle effects that have to be considered for accurate monitoring of the energy ratio of outgoing on-and off-line pulses. Detailed investigations have been performed on various measurement concepts potentially suited for deployment within future satellite missions.

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“…A similar approach, but using a piezo, was employed by Ref. [52]. We could not, however, achieve significant improvement.…”

Section: Lab Resultsmentioning

confidence: 92%

Energy calibration of integrated path differential absorption lidars

et al. 2018

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“…• A speckle reduction system shall be implemented. The necessity of this kind of system for ILS measurement is documented by Simon Potvin and Jérôme Genest [6].…”

Section: Virtual Conference 30 March-2 April 2021mentioning

confidence: 99%

Meteosat third generation infrared sounder (MTG-IRS), interferometer and spectrometer test outcomes, demonstration of the new 3D metrology system efficiency

Abdon

Gardette

Degrelle

et al. 2021

International Conference on Space Optics — ICSO 2020

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During the last decade, meteorology domain has lived many breakthroughs. In the field of remote sensing from space, one of the most significant advancement is in the use of Thermal Infrared sounders. Thales Alenia Space delivered sounders flagship METOP/IASI, resulting in the enhancement of meteorological events forecast and unprecedented 3D atmospheric knowledge.The next generation of European geostationary meteorological satellites, Meteosat Third Generation is currently being realized through the well-established and successful Cooperation between EUMETSAT and ESA with Thales Alenia Space being overall MTG prime contractor. MTG encompasses two kinds of satellites: an imaging mission MTG-I with the FCI imaging payload derived from the MSG-SEVIRI with a payload complement of a lightning detection system (LI as the Lightning Imager) and a sounding mission MTG-S with the payload complement including the thermal infrared sounding payload IRS (full disc coverage) and the Copernicus payload UVN/S4, a spectrometer in UV/VIS/NIR bands to retrieve air quality in Europe.Stemming from IASI, Thales Alenia Space is now developing the IRS interferometer as well as the detection and onboard processing chain. These key elements will be integrated by OHB which is the IRS instrument as well as MTG-S satellite Prime Contractor. Reaching performance from a geostationary orbit is a two-order of magnitude more stringent challenge compared to a LEO instrument. Thales Alenia Space did elaborate new and innovative technology to ensure sub nanometric interferometer metrology and thus to achieve real time on-board corrections.Two essential validation milestones have been achieved in 2019.• The interferometer engineering model was thoroughly tested successfully, especially in terms of spectral performance vs. microvibrations.• Thales Alenia Space has also tested the IRS "core spectrometer" engineering model, allowing to test the full spectrometer chain of the instrument by synchronizing the interferometer itself with the two 160x160 pixel detector arrays of the detection chain and the on-board data processing unit that is able to process the 2Gbit/s raw data flow generated by the instrument.The paper will focus on the two major outcomes of this test campaign:• The demonstration of the functionality of IRS new 3D metrology system, its associated processing and its benefits.• An overview of performances achieved during those two intensive test campaigns. In particular Spectral Response Function (SRF) knowledge/prediction, which is essential to support an unprecedented interpretation of the spectra and final products retrieval accuracy.

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“…Adding a dynamic variation on an element is a well-known method to average the speckle patterns [3][4][5][6][7][8][9]. Different speckle scrambler systems can be used.…”

Section: Solution Developed For Spatial Uniformity Optimizationmentioning

confidence: 99%

Speckle reduction system by using spatial and temporal scrambler in integrating sphere

Michel¹,

Carbo

Glastre³

et al. 2021

International Conference on Space Optics — ICSO 2020

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The OGSE GESTA (Geometrical and Spectral Test Assembly) operates in vacuum chamber to perform the optical characterization of the IRS instrument. GESTA integrates both sources, gas cell and laser sources, in order to perform a spectral characterization and calibration.The MTF measurements are performed by measuring the signal coming from a hot pattern plate, illuminated by a stable and homogeneous optical beam. To measure the background signal, the pattern plate is removed and a cryogenic blackbody is used instead of. This paper describes this illumination sub-system used in GESTA, developed by Bertin Technologies, and using the infrared laser sources. The principle of the used solution is to apply a dynamic variation to the interference status responsible for the speckle at the output of the integrating sphere, in order to eliminate the impact of the spatial coherence of the output beam and to get a uniform radiance through temporal averaging over the integration time of the optical detector.For that, the laser beams hit a rotating diffusing disc located inside the sphere. For GESTA, the requirement is challenging as speckle contrasts need to be as low as 0.1% for a 400μs integration time. The solution developed shows good enhancements, in terms of radiance level, stability, uniformity, and is easily translatable to other spectral ranges. Final achieved performances and the related influencing parameters are reported.

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Reducing the effect of integrating sphere speckle when characterizing the instrument line shape of a Fourier-transform hyperspectral imager

Cited by 6 publications

References 5 publications

Energy calibration of integrated path differential absorption lidars

Energy calibration of integrated path differential absorption lidars

Meteosat third generation infrared sounder (MTG-IRS), interferometer and spectrometer test outcomes, demonstration of the new 3D metrology system efficiency

Speckle reduction system by using spatial and temporal scrambler in integrating sphere

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