Analysis of the impact of air scattering on point source transmittance.

This paper proposes a method to simulate an average air scattering model by using random particles obeying a certain size spectrum and shape distribution, and it analyzes the influence of air scattering on the point source transmittance (PST) test using the model. The results of the analysis indicated that PST measurement errors caused by air scattering are directly proportional to the cube of the diameter of the optical system and that a one-level change in the air cleanliness may result in a one-order-of-magnitude change in the error. The cleanliness level of the measurement environment is less expensive and easier to obtain from analysis than from empirical values.