Proceedings Article | 29 July 2010
Proc. SPIE. 7732, Space Telescopes and Instrumentation 2010: Ultraviolet to Gamma Ray
KEYWORDS: Point spread functions, Telescopes, Mirrors, Multilayers, Metrology, Scattering, Light scattering, Bidirectional reflectance transmission function, Extreme ultraviolet, Charge-coupled devices
The Solar Ultraviolet Imager (SUVI) is one of several instruments being fabricated for use on board the upcoming
Geostationary Operational Environmental Satellites, GOES-R and -S platforms, as part of NOAA's space weather
monitoring fleet. SUVI is a Generalized Cassegrain telescope that employs multilayer coatings optimized to operate in
six extreme ultraviolet (EUV) narrow bandpasses centered at 93.9, 131.2, 171.1, 195.1, 284.2 and 303.8 Å. Over the
course of its operational lifetime SUVI will image and record full disk, EUV spectroheliograms approximately every few
minutes, and telemeter the data to the ground for digital processing. This data will be useful to scientists and engineers
wanting to better understand the effects of solar produced EUV radiation with the near-Earth environment. At the focus
of the SUVI telescope is a thin, back-illuminated CCD sensor with 21 μm (2.5 arc sec) pixels. At the shortest EUV
wavelengths, image degradation from mirror surface scatter effects due to residual optical fabrication errors dominate the
effects of both diffraction and geometrical aberrations. Discussed herein, we present a novel forward model that
incorporates: (i) application of a new unified surface scatter theory valid for moderately rough surfaces to predict the bidirectional
reflectance distribution function (BRDF) produced by each mirror (which uses optical surface metrology to
determine the power spectral density, PSD, that characterizes the "smoothness" of an optical surface); (ii) use of the
BRDF for each mirror at each EUV wavelength, in tandem with the optical design, to calculate the in-band point spread
function (PSF); (iii) use of the PSF to calculate the fractional ensquared energy in the focal plane of SUVI; (iv)
comparison of BRDF measurements taken at 93.9 Å with the forward model predictions and (v) final prediction of the
in-band, total system responsivity.
