Contamination scatter functions for stray-light analysis

Preliminary assessement of the atmospheric optical channel at goldstone (CA)

“…This is due to the fact that Mirror-4 was mounted facedown and therefore less prone to collect dust. Theoretical models were used to convert the BRDF to a contamination rate [13] yielding a rate of 0.033% dust deposition coverage per hour, which is consistent with published data at other observatories [14]. Dust deposition rate is an important parameter to consider because it helps determine how frequently the primary mirror needs to be cleaned given different operational scenarios and the required stray light tolerances to uphold receiver performance.…”

Towards a standardized method to assess straylight in earth observing optical instruments

“…Under normal incidence (=0), with very small roughness (<<1), a Taylor expansion of the exponential allows to recover equation (3). If the angular dependency is kept, for very small roughness we recover the formula given by Stover [10]:…”

“…A synthetic review of this subject has been presented by Dittman [3]. The dust particles, of random shape and orientation, are traditionally considered spherical to simplify the modeling, although it can be remarked that for a mirror surface, in principle two particles should be considered, the particle and its mirror image.…”

“…It is also assumed that the particles follow a log-log size distribution according to the MIL-1246B standard [4]. Dittman [3] discussed the possible use of two slope values (0.926 and 0.313) for respectively cleaned and uncleaned surfaces, as the cleaning process tends to remove preferably the largest particles. He also showed that Spyake and Wolfe [5] published BSDF curves are convolved with a finite detector aperture and thus should not be used as a starting point for a straylight model.…”

NIRSpec optics development: final report

“…The BRDF derivation from microroughness measurement has been modelized by Dittman [2] and has been used to anticipate the impact of the micro-roughness. However, this model appeared to be not fully applicable in presence of micro-scratches and other cosmetic defects.…”