The Aerosol Polarimetery Sensor (APS) is a nadir viewing, along-track observing, continuously operating electro-optical
polarimeter designed to measure earth and atmosphere scene spectral radiance in the visible (VIS) to short wave infrared
(SWIR) spectrum from an altitude of 705 km to permit collection of data for retrieval of operational Environmental Data
Records (EDRs). APS performance can be degraded due to light scatter, transmission, or reflectance changes caused by
contamination. Molecular films can cause scattering as well as spectrally selective absorption and reflectance
degradation. At short wavelengths, the molecular films may also create polarization changes. Raytheon developed and
implemented a contamination control program that ensured the APS sensor complied with cleanliness requirements.
Representative cleanliness monitoring results and lessons learned from the sensor integrated and tested at Space and
Airborne Systems El Segundo and Santa Barbara Remote Sensing (SBRS) are also presented.
Proc. SPIE. 6291, Optical Systems Degradation, Contamination, and Stray Light: Effects, Measurements, and Control II
KEYWORDS: Microscopes, Contamination, Statistical analysis, Data modeling, Aerospace engineering, Particles, Electroluminescence, Semiconducting wafers, Contamination control, Picture Archiving and Communication System
In contamination control technology relatively dirty surfaces cannot be specified with the same defining equations as those for "clean" surfaces. The current practices in the aerospace community disregard this inaccuracy in defining and specifying gradations of surface cleanliness. Using a 0.926 slope with an IEST-STD-CC1246D particle distribution to describe cleanliness on dirty surfaces, or surfaces subjected to fallout, is inaccurate, unrealistic, misleading, and often impossible to verify. Most importantly, using this model provides incorrect information to experts who calculate sensor performance: a slope of 0.926 is appropriate only for cleaned surfaces. However, the industry continues to use the same slope to describe all surfaces, clean or dirty. Current measurements taken from Raytheon labs have shown that particle distributions dominated by fallout typically have a slope between 0.3 and 0.5, in concurrence with previous studies. Based on the accumulated data, the authors propose that particle distributions for dirty surfaces be described by a second model, which should be incorporated into the next revision of IEST-STD-CC1246.