By definition, particles are visible (Î¼m-sized) conglomerations of matter that deposit onto surfaces exposed to the environment. In the colloquial sense, they are simply "dust." Particles are a natural part of the environment as is familiar to anyone who has ever dusted a mantelpiece or washed a car windshield. Modeling a particle as a sphere of arbitrary size, as shown in Figure 3-1, we see that the effect of the dust on the surface may be twofold.
First, the dust will prevent some light from reaching the underlying surface. Some effects of particulate contamination are therefore proportional to the surface obscuration, or the percent area coverage (PAC). Solar arrays, thermal control surfaces, and optical surfaces may all be degraded due to surface obscuration. Secondly, the particles may scatter light off of its original direction of travel. This is a critical concern for many optical systems.
Online access to SPIE eBooks is limited to subscribing institutions.