Characterization of fiber-based slit homogenizer devices in the NIR and SWIR

Amann, Simon; Duong-Ederer, Quynh; Haist, Tobias; Sierk, B.; Guldimann, Benedikt

doi:10.1117/12.2536147

Cited by 5 publications

(5 citation statements)

References 7 publications

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“…The primary purpose of these devices is the reduction of pseudo-noise from non-uniform scenes, which is another significant limitation of retrieval precision. The homogenization functionality and performance has been verified by extensive characterized measurements using an elaborate a test breadboard [20]. As can be seen evident from Figure 5, the entrance slit formed by the stacked array of optical fibers exhibits gaps of typically 30 µm between the individual across-track field-of views, which are due to the cladding around the fiber cores.…”

Section: Spatial Co-registration For Xco2 Observationsmentioning

confidence: 85%

The European CO2 Monitoring Mission: observing anthropogenic greenhouse gas emissions from space

Sierk

Bézy

Löscher

et al. 2019

International Conference on Space Optics — ICSO 2018

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Responding to plans of the European Commission for extending the observation capabilities of the Copernicus programme, the European Space Agency (ESA) has initiated Phase A industrial (technical feasibility) studies for several new space-borne Earth Observation missions. High priority is given to a constellation of LEO satellites in Sunsynchronous orbit with the purpose of observing anthropogenic carbon dioxide (CO2) emissions [European Commission, 2017]. The observing system shall acquire images of CO2 concentration in terms of dry air column-averaged mole fractions (XCO2), providing complete global land coverage at high spatial resolution (4 km 2 ) within five days. The demanding requirements call for a payload comprising a combination of multiple instruments, which perform simultaneous measurements. The XCO2 is inferred from reflectance measurements in the Near-Infrared (NIR) and Short-Wave Infrared spectral regions (SWIR). This requires at least three spatially co-registered push-broom imaging spectrometers, measuring spectral radiance and solar irradiance in the NIR (747-773 nm), SWIR-1 (1595-1675 nm) and SWIR-2 (1990SWIR-2 ( -2095 at moderate spectral resolving power (R~5000-7000). In addition, the observations for CO2 concentration will be complemented by Differential Optical Absorption Spectroscopy (DOAS) measurements of nitrogen dioxide (NO2) over the same area. The NO2 measurements in the visible region (400-500 nm) are expected to serve as a tracer for plumes of high CO2 concentration resulting from high temperature combustion, which will facilitate plume identification and mapping. The third component of the payload is a multiple-angle polarimeter (MAP), performing high-precision measurements of aerosol (and cloud) properties. Its measurements of polarized radiance under various observation angles are expected to reduce XCO2 bias error and significantly increase the yield of useful retrievals from the NIR and SWIR spectra. The complex observation architecture, involving multiple instruments and platforms, call for optimized observational requirements, driven by the primary goal of detecting and quantifying point-sources of greenhouse gas emissions. In particular, high single-sounding precision is essential for identifying plumes of elevated CO2 concentration from instantaneous image acquisitions without regional and temporal averaging. This translates into stringent requirements for Signal-to-noise ratio (SNR), as well as spatial co-registration and spectral stability, which drive the instrument design. The presentation will introduce the different elements of the candidate Copernicus mission, in view of the ambitious mission goals. The payload components and observation requirements are addressed with special emphasis on the derivation of the SNR and spectral resolution requirements, which determine the instrument sizing.

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Section: Spatial Co-registration For Xco2 Observationsmentioning

confidence: 85%

The European CO2 Monitoring Mission: observing anthropogenic greenhouse gas emissions from space

Sierk

Bézy

Löscher

et al. 2019

International Conference on Space Optics — ICSO 2018

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“…Apart from the mirror-based SH discussed in this study, future remote sensing instruments investigate the technology of another slit homogenizer technology, which is based on rectangular multimode fiber bundles. These devices are based on the same principle as the mirror-based SH but enable one to homogenize the scene in the ACT and ALT direction (Amann et al, 2019) and provide enhanced performance over extreme albedo variations.…”

Section: Resultsmentioning

confidence: 99%

Slit homogenizer introduced performance gain analysis based on the Sentinel-5/UVNS spectrometer

et al. 2021

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Abstract. Spatially heterogeneous Earth radiance scenes affect the atmospheric composition measurements of high-resolution Earth observation spectrometer missions. The scene heterogeneity creates a pseudo-random deformation of the instrument spectral response function (ISRF). The ISRF is the direct link between the forward radiative transfer model, used to retrieve the atmospheric state, and the spectra measured by the instrument. Hence, distortions of the ISRF owing to radiometric inhomogeneity of the imaged Earth scene will degrade the precision of the Level-2 retrievals. Therefore, the spectral requirements of an instrument are often parameterized in the knowledge of the ISRF over non-uniform scenes in terms of shape, centroid position of the spectral channel and the full width at half maximum (FWHM). The Sentinel-5/UVNS instrument is the first push-broom spectrometer that makes use of a concept referred to as a slit homogenizer (SH) for the mitigation of spatially non-uniform scenes. This is done by employing a spectrometer slit formed by two parallel mirrors scrambling the scene in the along track direction (ALT) and hence averaging the scene contrast only in the spectral direction. The flat mirrors do not affect imaging in the across track direction (ACT) and thus preserve the spatial information in that direction. The multiple reflections inside the SH act as coherent virtual light sources and the resulting interference pattern at the SH exit plane can be described by simulations using scalar diffraction theory. By homogenizing the slit illumination, the SH strongly modifies the spectrograph pupil illumination as a function of the input scene. In this work we investigate the impact and strength of the variations of the spectrograph pupil illumination for different scene cases and quantify the impact on the ISRF stability for different types of aberration present in the spectrograph optics.

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“…The slit is composed of an array of rectangular optical multimode fibers, whose principal function is to homogenise the spatially heterogeneous input scene by multiple reflections along the propagation within the fibres. Such devices have been shown to efficiently average out scene contrast and assure a homogeneous output image of the slit [24], which results in highly stable instrument spectral response functions (ISRF). The fibre-based slit, which is also referred to as two-dimensional slit homogeniser (2DSH), is described in further detail in section 3.1.3.…”

Section: Co2i and No2i Designmentioning

confidence: 99%

“…CO2M will be the first Earth observation mission deploying a novel kind of entrance slit in its imaging spectrometers, which is based on optical multi-mode fibres [24]. The rationale of this technology is to perform a piece-wise homogenisation of the input scene in both, the spectral and spatial direction, in order to obtain a stable, scene-independent Instrument Spectral Response Function (ILRS).…”

Section: Fibre-based Entrance Slitmentioning

confidence: 99%

The Copernicus CO2M mission for monitoring anthropogenic carbon dioxide emissions from space

Sierk

Fernandez²,

Bézy³

et al. 2021

International Conference on Space Optics — ICSO 2020

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The European Space Agency (ESA), in collaboration with the European Commission (EC) and EUMETSAT, is developing a space-borne observing system for quantification of anthropogenic carbon dioxide (CO 2 ) emissions. Forming part of the EC's Copernicus programme, the CO 2 monitoring (CO2M) mission will be implemented as a constellation of identical satellites, to be operated over a period of at least 7 years and measuring CO 2 concentration in terms of column-averaged mole fraction (denoted as XCO 2 ). Each satellite will continuously image XCO 2 along the satellite track on the sun-illuminated part of the orbit, with a swath width of >250 km. Observations will be provided at a spatial resolution of 2 x 2 km 2 , with high precision (<0.7 ppm) and accuracy (bias <0.5 ppm). To this end, the payload comprises a suite of instruments addressing the various aspects of the challenging observation requirements: A push-broom imaging spectrometer will perform co-located measurements of top-of-atmosphere radiances in the Near Infrared (NIR) and Short-Wave Infrared (SWIR) at high to moderate spectral resolution

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Characterization of fiber-based slit homogenizer devices in the NIR and SWIR

Cited by 5 publications

References 7 publications

The European CO2 Monitoring Mission: observing anthropogenic greenhouse gas emissions from space

The European CO2 Monitoring Mission: observing anthropogenic greenhouse gas emissions from space

Slit homogenizer introduced performance gain analysis based on the Sentinel-5/UVNS spectrometer

The Copernicus CO2M mission for monitoring anthropogenic carbon dioxide emissions from space

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