System-level pre-launch calibration of onboard solar diffusers

Robert A. Barnes; Steven W. Brown; Keith R. Lykke; Gerald T. Fraser; James J. Butler

doi:10.1117/12.731804

26 September 2007 System-level pre-launch calibration of onboard solar diffusers

Robert A. Barnes, Steven W. Brown, Keith R. Lykke, Gerald T. Fraser, James J. Butler

Proceedings Volume 6677, Earth Observing Systems XII; 667704 (2007) https://doi.org/10.1117/12.731804
Event: Optical Engineering + Applications, 2007, San Diego, California, United States

Abstract

Onboard diffuse reflecting plaques are carried to orbit as radiometric reference standards for Earth-observing satellite instruments. For many instruments the reflectance properties of the plaque are characterized independently of the instrument, and the effects of scattering by the diffuser housing are determined through mathematical modeling. The pre-launch laboratory calibration of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) included a system-level calibration of the onboard diffuser using an external lamp and a reference plaque at the sensor's Earth-view port. The calibration of the onboard diffuser was made relative to the reference plaque using SeaWiFS as a transfer radiometer. Recent developments in laboratory light sources enable a significant improvement to the SeaWiFS calibration technique. These include sets of fiber-optically coupled tunable lasers that illuminate integrating spheres or the prime focus of a collimator, to produce uniform, high radiant flux Lambertian or collimated sources, respectively. In addition, newly developed, spectrally tunable supercontinuum-based light sources can provide sets of radiance spectra for the collimator to validate the laser-based diffuser calibration. An absolute calibration of the diffuser system in the laboratory also provides the first step in a two-part transfer-to-orbit experiment, in which the second step uses the illumination of the diffuser on orbit by the Sun. For hyperspectral instruments, the laboratory calibration must account for spectral artifacts in the diffuser material. For on-orbit measurements, the calibration must account for the effects of Earth-shine as a contaminating source of irradiance illuminating the diffuser.

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Robert A. Barnes, Steven W. Brown, Keith R. Lykke, Gerald T. Fraser, and James J. Butler "System-level pre-launch calibration of onboard solar diffusers", Proc. SPIE 6677, Earth Observing Systems XII, 667704 (26 September 2007); https://doi.org/10.1117/12.731804

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KEYWORDS

Calibration

Diffusers

Collimators

Sensors

Integrating spheres

Alternate lighting of surfaces

Optical spheres

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