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

Abstract

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.