S. Chatterje, Indian Institute of Astrophysics, subhamoy@iiap.res.in
  A. Ramaprakash, IUCAA, Pune, anr@iucaa.in
  A. Khan, IUCAA, Pune, aafaque.rk@gmail.com
  D. Tripathy, IUCAA, Pune, durgesh@iucaa.in
  D. Banerjee, IIA, Bangalore, dipu@iiap.res.in

Solar Ultraviolet Imaging Telescope (SUIT), a proposed payload for ADITYA L1 mission, is intended to image full solar disc through 11 narrowband and broadband filters in near UV (200 nm-400 nm). It has an off-axis Ritchey-Chretien configuration. Being an ultraviolet imager it is crucial to analyse how scatter due to optical surface microroughness and edges present in the optical path degrade the image quality in terms of contrast and spatial resolution. Experimental 1D Power Spectral Density (PSD) data of a polished optical surface with 15 angstroms RMS microroughness has been fitted to an 1D K-correlation PSD model and has been converted to a 2D PSD considering rotational symmetry. These PSD model parameters have been fed to a scattering simulation software called ASAP to create a K-correlation Bidirectional Scattering Distribution Function and to estimate the scatter within solar disc region. Considering an allowable scatter to specular ratio within disc to be utmost 0.3%, optical surface microroughness requirement has been calculated keeping the PSD nature same as that for fit to experimental data. Isotropic polynomial model has been applied to model scatter due to baffle inner surface paint and also the edges. Scatter coming from edges and baffle inner surfaces has been found to be negligible compared to that due to optical surface microroughness. Simulation showed the scatter to be dominated by primary and secondary mirror as expected. Point Spread Function wing broadening due to scatter has also been estimated to understand whether it affects the spatial resolution.