Dr. Steven Delwart Profile

Dr. Steven Delwart

Optical Instrument Engineer at European Space Research and Technology Ctr

SPIE Involvement:

Author

Publications (13)

Proceedings Article | 21 November 2017 Open Access

Enhancement of diffusers BRDF accuracy

Gerard Otter, Gregory Bazalgette Courrèges-Lacoste, Hedser van Brug, Jos Groote Schaarsberg, Steven Delwart, Umberto del Bello

Proceedings Volume 10567, 1056740 (2017) https://doi.org/10.1117/12.2308087

KEYWORDS: Diffusers, Bidirectional reflectance transmission function, Current controlled current source, Astronomical imaging, Simulation of CCA and DLA aggregates

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Proceedings Article | 23 September 2013 Paper

MERIS calibrations: 10 years

S. Delwart, L. Bourg

Proceedings Volume 8866, 88660Y (2013) https://doi.org/10.1117/12.2022285

KEYWORDS: Calibration, Diffusers, Instrument modeling, Data modeling, Neodymium, Erbium, Ions, Cameras, Bidirectional reflectance transmission function, Sun

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Proceedings Article | 12 October 2011 Paper

Radiometric calibration of MERIS

S. Delwart, Lu. Bourg

Proceedings Volume 8176, 817613 (2011) https://doi.org/10.1117/12.895090

KEYWORDS: Calibration, Diffusers, Data modeling, Bidirectional reflectance transmission function, Instrument modeling, Solar radiation models, Cameras, Spectroscopy, Spectral models, Atmospheric modeling

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Proceedings Article | 23 September 2009 Paper

Radiometric calibration of MERIS

Steven Delwart, Ludovic Bourg

Proceedings Volume 7474, 74740U (2009) https://doi.org/10.1117/12.830962

KEYWORDS: Diffusers, Calibration, Bidirectional reflectance transmission function, Data modeling, Instrument modeling, Cameras, Sun, Performance modeling, Modeling, Data acquisition

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Proceedings Article | 13 October 2006 Paper

Enhancement of diffusers BSDF accuracy: spectral features effect

Hedser van Brug, Grégory Bazalgette Courrèges-Lacoste, Gerard Otter, Jos Schaarsberg, Steven Delwart, Umberto del Bello

Proceedings Volume 6361, 636111 (2006) https://doi.org/10.1117/12.689809

KEYWORDS: Diffusers, Spectrometers, Data modeling, Sensors, Speckle pattern, Satellites, Speckle, Scattering, Sun, Calibration

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This paper reports the activities performed in the framework of the ESA contract 18432/04/NL/AR: Enhancement of diffusers BSDF Accuracy. This study was conducted to investigate properties of various diffusers. Diffusers are widely used in space instruments as part of the on-board absolute calibration. Knowledge of the behavior of the diffuser is therefore most important. From measurements of launched instruments in-orbit it has been discovered that when a diffuser is used in the vacuum of space the BSDF (Bi-directional Scattering Distribution Function) can change with respect to the one in ambient conditions. This is called the air/vacuum effect and has been simulated in this study by measuring the BSDF in a laboratory in ambient as well as vacuum conditions, results of this part of the study will be reported. Another effect on the BSDF is not related to the air/vacuum effect, but to the design parameters of the optical system and the scattering properties of the diffuser. The effect is called Spectral Features and is a noise like structure superimposed on the BSDF. To observe this effect, spectral and spatial (partially) coherence light is needed. High-resolution spectrometers provide the spectral coherence and a narrow field of view provides the spatial coherence. Modern space spectrometers have high spectral resolution and/or a small field of view (high spatial resolution). Different diffusers create different speckle patterns leading to different Spectral Features amplitudes. Therefore the choice of diffuser can be very critical with respect to the required absolute radiometric calibration of an instrument. Even if the Spectral Features are small it can influence the error budget of the retrieval algorithms for the level 2 products. In this presentation diffuser trade-off results are presented and the Spectral Features model applied to the optical configuration of the MERIS instrument is compared to in-flight measurements of MERIS. The introduction describes the use of diffusers in earth-observation satellites and why they cause spectral features. In Sec.2 the physical background of the spectral features, speckles, is discussed. Section 3 shows the results from air/vacuum effect measurements (SubSec.3.1), spectral features amplitude measurements on our in-house setup and simulations in a single graphical display (SubSec.3.2 ), and the measured and simulated results for the MERIS instrument (SubSec.3.3). The following sections deal with a description of the measuring setup and the model that has been made to do the simulations. Finally, in the discussion, topics like what is the best diffuser and what can be done to minimize the amplitude of the spectral features will be dealt with.

Proceedings Article | 4 November 2004 Paper

Radiometric calibration of MERIS

Steven Delwart, Ludovic Bourg

Proceedings Volume 5570, (2004) https://doi.org/10.1117/12.567989

KEYWORDS: Calibration, Diffusers, Bidirectional reflectance transmission function, Data modeling, Instrument modeling, Reflectivity, Sun, Solar radiation models, Satellites, Spectroscopy

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Proceedings Article | 4 November 2004 Paper

Assessment of long-term vicarious calibration efforts of MERIS on land product quality

Michael Schaepman, Raul Zurita-Milla, Mathias Kneubuehler, Jan Clevers, Steven Delwart

Proceedings Volume 5570, (2004) https://doi.org/10.1117/12.566582

KEYWORDS: Calibration, Virtual colonoscopy, Databases, Image classification, Image filtering, Satellites, Sensors, Reflectivity, Optical filters, Spatial resolution

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Proceedings Article | 4 November 2004 Paper

MERIS spectral calibration campaigns

Steven Delwart, Ludovic Bourg, Rene Preusker, Richard Santer

Proceedings Volume 5570, (2004) https://doi.org/10.1117/12.567991

KEYWORDS: Spectral calibration, Diffusers, Absorption, Erbium, Cameras, Calibration, Spectroscopy, Oxygen, Spectral models, Sensors

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Proceedings Article | 2 February 2004 Paper

MERIS 1st year: early calibration results

Steven Delwart, Ludovic Bourg, Jean-Paul Huot

Proceedings Volume 5234, (2004) https://doi.org/10.1117/12.508485

KEYWORDS: Diffusers, Calibration, Bidirectional reflectance transmission function, Data modeling, Cameras, Spectral calibration, Spectroscopy, Sun, Absorption, Sensors

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SPIE Journal Paper | 1 December 2003

Modeling of Spectralon diffusers for radiometric calibration in remote sensing

Grégory Bazalgette Courrège-Lacoste, Jos Groote-Schaarsberg, Rudolf Sprik, Steven Delwart

OE, Vol. 42, Issue 12, (December 2003) https://doi.org/10.1117/12.10.1117/1.1622961

KEYWORDS: Diffusers, Bidirectional reflectance transmission function, Scattering, Calibration, Silicon, Ultraviolet radiation, Radiative transfer, Data modeling, Sensors, Telescopic pixel displays

Proceedings Article | 8 April 2003 Paper

Calibration and early results of MERIS on ENVISAT

Steven Delwart, Jean-Paul Huot, L. Bourg

Proceedings Volume 4881, (2003) https://doi.org/10.1117/12.462619

KEYWORDS: Diffusers, Calibration, Bidirectional reflectance transmission function, Erbium, Spectroscopy, Spectral calibration, Sun, Spectral models, Sensors, Data modeling

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