Optical System Design of a Wide Field-of-View Camera for the Characterization of Earth’s Reflected Solar Radiation

Smeesters

et al. 2021

Sensors

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The measurement of the Earth’s Outgoing Longwave Radiation plays a key role in climate change monitoring. This measurement requires a compact wide-field-of-view camera, covering the 8–14 µm wavelength range, which is not commercially available. Therefore, we present a novel thermal wide-field-of-view camera optimized for space applications, featuring a field of view of 140° to image the Earth from limb to limb, while enabling a high spatial resolution of 4.455 km at nadir. Our cost-effective design comprises three germanium lenses, of which only one has a single aspherical surface. It delivers a very good image quality, as shown by the nearly-diffraction-limited performance. Radiative transfer simulations indicate excellent performance of our camera design, enabling an estimate of the broadband Outgoing Longwave Radiation with a random relative error of 4.8%.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Wide-Field-of-View Longwave Camera for the Characterization of the Earth’s Outgoing Longwave Radiation

Smeesters

et al. 2021

Sensors

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“…accurately the total Earth's outgoing energy. 11 This radiometer is supplemented with high-resolution shortwave (SW, [400-1100] nm), 12 and longwave (LW, [8][9][10][11][12][13][14] µm) WFOV cameras, improving the radiometer accuracy, increasing the spatial resolution, and enbabling the spectral separation between Reflected Solar Radiation (RSR) and Outgoing Longwave Radiation (OLR). This paper compares the design and performance of 2 WFOV radiometer configurations: (1) our in-house developed cavity radiometer of which the interior is coated with Black Velvet and (2) an integrating sphere design measuring radiation after multiple-reflections on the interior Spectralon coating.…”

Section: Virtual Conference 30 March-2 April 2021mentioning

confidence: 99%

Towards a next-generation Earth Radiation Budget radiometer by optimization of the cavity geometry and coating

Smeesters²,

International Conference on Space Optics — ICSO 2020

et al. 2021

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Climate on Earth is determined by the Earth Radiation Budget (ERB), which quantifies the incoming and outgoing radiative energy fluxes at the top-of-atmosphere. The ERB can be monitored from space by nonscanning wide field-of-view radiometers, or by scanning narrow field-of-view radiometers. In this paper, we investigate the use of two wide field-of-view radiometers geometries, each of which composed of a baffle and precision aperture featuring a field-of-view of minimally of 127 • , allowing to monitor the Earth's radiative fluxes from limb-to-limb, from an altitude of about 700 km. Our first radiometer composes a near-hemispherical cavity enabling a uniform angular sensitivity, in combination with a conical part and baffle to ensure a wide field-ofview. For the second radiometer design, we consider an integrating sphere supplemented with an active-cavity radiometer positioned at an angle of 90 • from the precision aperture. Both designs are equipped with practical coating materials, i.e. Black Velvet for the near-spherical radiometer and Spectralon for the integrating sphere. For both designs, the cavity geometry is analyzed and an evaluation of the interior cavity coatings is made. To compare both designs, we evaluate the optical absorbance by relying on scattering analyses. To conclude, we present an evaluation of both radiometer designs, comprising an analysis of the coating properties, giving valuable input for the next-generation Earth Radiation Budget radiometers.

“…Our previous research efforts have already addressed innovative spaceborne instrumentation with the aim of improving climate change monitoring by means of a better assessment of the Earth’s radiation budget. These instruments include (1) a radiometer to measure the total incoming solar radiation and total outgoing terrestrial radiation [ 14 ], (2) a first camera to measure shortwave radiation [ 15 ], and (3) a second camera to measure longwave radiation [ 16 ]. These three instruments are part of our space mission project named the Earth Climate Observatory (ECO) (previously known as ASTERIX [ 17 ]).…”

Section: Introductionmentioning

confidence: 99%

Optical Design of a Novel Wide-Field-of-View Space-Based Spectrometer for Climate Monitoring

Dewitte

et al. 2022

Sensors

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We report on a near-infrared imaging spectrometer for sensing the three most prominent greenhouse gases in the atmosphere (water vapor, carbon dioxide and methane). The optical design of the spectrometer involves freeform optics, which enables achieving exceptional performance and allows progressing well beyond the state-of-the-art in terms of compactness, field-of-view, and spatial resolution. The spectrometer is intended to be launched on a small satellite orbiting at 700 km and observing the Earth with a wide field-of-view of 120° and a spatial resolution of 2.6 km at nadir. The satellite will ultimately allow for improved climate change monitoring.